title: sshd_config(5)

summary: OpenSSH daemon configuration file

text:
# sshd_config(5)

## NAME
sshd_config — OpenSSH daemon configuration file

## DESCRIPTION
sshd(8) reads configuration data from /etc/openssh/sshd_config (or the file specified with -f on the command line). The file contains keyword-argument pairs, one per line. Unless noted otherwise, for each keyword, the first obtained value will be used. Lines starting with ‘#’ and empty lines are interpreted as comments. Arguments may optionally be enclosed in double quotes (") in order to represent arguments containing spaces.

The possible keywords and their meanings are as follows (note that keywords are case-insensitive and arguments are case-sensitive):

AcceptEnv

Specifies what environment variables sent by the client will be copied into the session's environ(7). See SendEnv and SetEnv in ssh_config(5) for how to configure the client. The TERM environment variable is always accepted whenever the client requests a pseudo-terminal as it is required by the protocol. Variables are specified by name, which may contain the wildcard characters ‘*’ and ‘?’. Multiple environment variables may be separated by whitespace or spread across multiple AcceptEnv directives. Be warned that some environment variables could be used to bypass restricted user environments. For this reason, care should be taken in the use of this directive. The default is not to accept any environment variables.

AddressFamily

Specifies which address family should be used by sshd(8). Valid arguments are any (the default), inet (use IPv4 only), or inet6 (use IPv6 only).

AllowAgentForwarding

Specifies whether ssh-agent(1) forwarding is permitted. The default is yes. Note that disabling agent forwarding does not improve security unless users are also denied shell access, as they can always install their own forwarders.

AllowGroups

This keyword can be followed by a list of group name patterns, separated by spaces. If specified, login is allowed only for users whose primary group or supplementary group list matches one of the patterns. Only group names are valid; a numerical group ID is not recognized. By default, login is allowed for all groups. The allow/deny groups directives are processed in the following order: DenyGroups, AllowGroups. See PATTERNS in ssh_config(5) for more information on patterns. This keyword may appear multiple times in sshd_config with each instance appending to the list.

AllowStreamLocalForwarding

Specifies whether StreamLocal (Unix-domain socket) forwarding is permitted. The available options are yes (the default) or all to allow StreamLocal forwarding, no to prevent all StreamLocal forwarding, local to allow local (from the perspective of ssh(1)) forwarding only or remote to allow remote forwarding only. Note that disabling StreamLocal forwarding does not improve security unless users are also denied shell access, as they can always install their own forwarders.

AllowTcpForwarding

Specifies whether TCP forwarding is permitted. The available options are yes (the default) or all to allow TCP forwarding, no to prevent all TCP forwarding, local to allow local (from the perspective of ssh(1)) forwarding only or remote to allow remote forwarding only. Note that disabling TCP forwarding does not improve security unless users are also denied shell access, as they can always install their own forwarders.

AllowUsers

This keyword can be followed by a list of user name patterns, separated by spaces. If specified, login is allowed only for user names that match one of the patterns. Only user names are valid; a numerical user ID is not recognized. By default, login is allowed for all users. If the pattern takes the form USER@HOST then USER and HOST are separately checked, restricting logins to particular users from particular hosts. HOST criteria may additionally contain addresses to match in CIDR address/masklen format. The allow/deny users directives are processed in the following order: DenyUsers, AllowUsers. See PATTERNS in ssh_config(5) for more information on patterns. This keyword may appear multiple times in sshd_config with each instance appending to the list.

AuthenticationMethods

Specifies the authentication methods that must be successfully completed for a user to be granted access. This option must be followed by one or more lists of comma-separated authentication method names, or by the single string any to indicate the default behaviour of accepting any single authentication method. If the default is overridden, then successful authentication requires completion of every method in at least one of these lists. For example, "publickey,password publickey,keyboard-interactive" would require the user to complete public key authentication, followed by either password or keyboard interactive authentication. Only methods that are next in one or more lists are offered at each stage, so for this example it would not be possible to attempt password or keyboard-interactive authentication before public key.

For keyboard interactive authentication it is also possible to restrict authentication to a specific device by appending a colon followed by the device identifier bsdauth or pam. depending on the server configuration. For example, "keyboard-interactive:bsdauth" would restrict keyboard interactive authentication to the bsdauth device.

If the publickey method is listed more than once, sshd(8) verifies that keys that have been used successfully are not reused for subsequent authentications. For example, "publickey,publickey" requires successful authentication using two different public keys.

Note that each authentication method listed should also be explicitly enabled in the configuration.

The available authentication methods are: "gssapi-with-mic", "hostbased", "keyboard-interactive", "none" (used for access to password-less accounts when PermitEmptyPasswords is enabled), "password" and "publickey".

AuthorizedKeysCommand

Specifies a program to be used to look up the user's public keys. The program must be owned by root, not writable by group or others and specified by an absolute path. Arguments to AuthorizedKeysCommand accept the tokens described in the TOKENS section. If no arguments are specified then the username of the target user is used. The program should produce on standard output zero or more lines of authorized_keys output (see AUTHORIZED_KEYS in sshd(8)). AuthorizedKeysCommand is tried after the usual AuthorizedKeysFile files and will not be executed if a matching key is found there. By default, no AuthorizedKeysCommand is run.

AuthorizedKeysCommandUser

Specifies the user under whose account the AuthorizedKeysCommand is run. It is recommended to use a dedicated user that has no other role on the host than running authorized keys commands. If AuthorizedKeysCommand is specified but AuthorizedKeysCommandUser is not, then sshd(8) will refuse to start.

AuthorizedKeysFile

Specifies the file that contains the public keys used for user authentication. The format is described in the AUTHORIZED_KEYS FILE FORMAT section of sshd(8). Arguments to AuthorizedKeysFile accept the tokens described in the TOKENS section. After expansion, AuthorizedKeysFile is taken to be an absolute path or one relative to the user's home directory. Multiple files may be listed, separated by whitespace. Alternately this option may be set to none to skip checking for user keys in files. The default is "/etc/openssh/authorized_keys/%u /etc/openssh/authorized_keys2/%u .ssh/authorized_keys .ssh/authorized_keys2".

AuthorizedPrincipalsCommand

Specifies a program to be used to generate the list of allowed certificate principals as per AuthorizedPrincipalsFile. The program must be owned by root, not writable by group or others and specified by an absolute path. Arguments to AuthorizedPrincipalsCommand accept the tokens described in the TOKENS section. If no arguments are specified then the username of the target user is used. The program should produce on standard output zero or more lines of AuthorizedPrincipalsFile output. If either AuthorizedPrincipalsCommand or AuthorizedPrincipalsFile is specified, then certificates offered by the client for authentication must contain a principal that is listed. By default, no AuthorizedPrincipalsCommand is run.

AuthorizedPrincipalsCommandUser

Specifies the user under whose account the AuthorizedPrincipalsCommand is run. It is recommended to use a dedicated user that has no other role on the host than running authorized principals commands. If AuthorizedPrincipalsCommand is specified but AuthorizedPrincipalsCommandUser is not, then sshd(8) will refuse to start.

AuthorizedPrincipalsFile

Specifies a file that lists principal names that are accepted for certificate authentication. When using certificates signed by a key listed in TrustedUserCAKeys, this file lists names, one of which must appear in the certificate for it to be accepted for authentication. Names are listed one per line preceded by key options (as described in AUTHORIZED_KEYS FILE FORMAT in sshd(8)). Empty lines and comments starting with ‘#’ are ignored. Arguments to AuthorizedPrincipalsFile accept the tokens described in the TOKENS section. After expansion, AuthorizedPrincipalsFile is taken to be an absolute path or one relative to the user's home directory. The default is none, i.e. not to use a principals file – in this case, the username of the user must appear in a certificate's principals list for it to be accepted.

Note that AuthorizedPrincipalsFile is only used when authentication proceeds using a CA listed in TrustedUserCAKeys and is not consulted for certification authorities trusted via ~/.ssh/authorized_keys or /etc/openssh/authorized_keys/, though the principals= key option offers a similar facility (see sshd(8) for details).

Banner

The contents of the specified file are sent to the remote user before authentication is allowed. If the argument is none then no banner is displayed. By default, no banner is displayed.

CASignatureAlgorithms

Specifies which algorithms are allowed for signing of certificates by certificate authorities (CAs). The default is:

```
ssh-ed25519,ecdsa-sha2-nistp256,
ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
sk-ssh-ed25519@openssh.com,
sk-ecdsa-sha2-nistp256@openssh.com,
rsa-sha2-512,rsa-sha2-256
```

If the specified list begins with a ‘+’ character, then the specified algorithms will be appended to the default set instead of replacing them. If the specified list begins with a ‘-’ character, then the specified algorithms (including wildcards) will be removed from the default set instead of replacing them.

Certificates signed using other algorithms will not be accepted for public key or host-based authentication.

ChannelTimeout

Specifies whether and how quickly sshd(8) should close inactive channels. Timeouts are specified as one or more “type=interval” pairs separated by whitespace, where the “type” must be a channel type name (as described in the table below), optionally containing wildcard characters. The timeout value “interval” is specified in seconds or may use any of the units documented in the TIME FORMATS section. For example, “session:*=5m” would cause all sessions to terminate after five minutes of inactivity. Specifying a zero value disables the inactivity timeout.

The available channel types include:

agent-connection

Open connections to ssh-agent(1).

direct-tcpip, direct-streamlocal@openssh.com

Open TCP or Unix socket (respectively) connections that have been established from a ssh(1) local forwarding, i.e. LocalForward or DynamicForward.

forwarded-tcpip, forwarded-streamlocal@openssh.com

Open TCP or Unix socket (respectively) connections that have been established to a sshd(8) listening on behalf of a ssh(1) remote forwarding, i.e. RemoteForward.

session:command

Command execution sessions.

session:shell

Interactive shell sessions.

session:subsystem:...

Subsystem sessions, e.g. for sftp(1), which could be identified as session:subsystem:sftp.

x11-connection

Open X11 forwarding sessions.

Note that in all the above cases, terminating an inactive session does not guarantee to remove all resources associated with the session, e.g. shell processes or X11 clients relating to the session may continue to execute.

Moreover, terminating an inactive channel or session does not necessarily close the SSH connection, nor does it prevent a client from requesting another channel of the same type. In particular, expiring an inactive forwarding session does not prevent another identical forwarding from being subsequently created. See also UnusedConnectionTimeout, which may be used in conjunction with this option.

The default is not to expire channels of any type for inactivity.

ChrootDirectory

Specifies the pathname of a directory to chroot(2) to after authentication. At session startup sshd(8) checks that all components of the pathname are root-owned directories which are not writable by any other user or group. After the chroot, sshd(8) changes the working directory to the user's home directory. Arguments to ChrootDirectory accept the tokens described in the TOKENS section. The ChrootDirectory must contain the necessary files and directories to support the user's session. For an interactive session this requires at least a shell, typically sh(1), and basic /dev nodes such as null(4), zero(4), stdin(4), stdout(4), stderr(4), and tty(4) devices. For file transfer sessions using SFTP no additional configuration of the environment is necessary if the in-process sftp-server is used, though sessions which use logging may require /dev/log inside the chroot directory on some operating systems (see sftp-server(8) for details).

For safety, it is very important that the directory hierarchy be prevented from modification by other processes on the system (especially those outside the jail). Misconfiguration can lead to unsafe environments which sshd(8) cannot detect.

The default is none, indicating not to chroot(2).

Ciphers

Specifies the ciphers allowed. Multiple ciphers must be comma-separated. If the specified list begins with a ‘+’ character, then the specified ciphers will be appended to the default set instead of replacing them. If the specified list begins with a ‘-’ character, then the specified ciphers (including wildcards) will be removed from the default set instead of replacing them. If the specified list begins with a ‘^’ character, then the specified ciphers will be placed at the head of the default set. The supported ciphers are:

- 3des-cbc

- aes128-cbc

- aes192-cbc

- aes256-cbc

- aes128-ctr

- aes192-ctr

- aes256-ctr

- aes128-gcm@openssh.com

- aes256-gcm@openssh.com

- chacha20-poly1305@openssh.com

The default is:

```
chacha20-poly1305@openssh.com,
aes256-gcm@openssh.com,aes128-gcm@openssh.com,
aes256-ctr,aes192-ctr,aes128-ctr
```

The list of available ciphers may also be obtained using "ssh -Q cipher".

ClientAliveCountMax

Sets the number of client alive messages which may be sent without sshd(8) receiving any messages back from the client. If this threshold is reached while client alive messages are being sent, sshd will disconnect the client, terminating the session. It is important to note that the use of client alive messages is very different from TCPKeepAlive. The client alive messages are sent through the encrypted channel and therefore will not be spoofable. The TCP keepalive option enabled by TCPKeepAlive is spoofable. The client alive mechanism is valuable when the client or server depend on knowing when a connection has become unresponsive. The default value is 3. If ClientAliveInterval is set to 15, and ClientAliveCountMax is left at the default, unresponsive SSH clients will be disconnected after approximately 45 seconds. Setting a zero ClientAliveCountMax disables connection termination.

ClientAliveInterval

Sets a timeout interval in seconds after which if no data has been received from the client, sshd(8) will send a message through the encrypted channel to request a response from the client. The default is 0, indicating that these messages will not be sent to the client.

Compression

Specifies whether compression is enabled after the user has authenticated successfully. The argument must be yes, delayed (a legacy synonym for yes) or no. The default is yes.

DenyGroups

This keyword can be followed by a list of group name patterns, separated by spaces. Login is disallowed for users whose primary group or supplementary group list matches one of the patterns. Only group names are valid; a numerical group ID is not recognized. By default, login is allowed for all groups. The allow/deny groups directives are processed in the following order: DenyGroups, AllowGroups. See PATTERNS in ssh_config(5) for more information on patterns. This keyword may appear multiple times in sshd_config with each instance appending to the list.

DenyUsers

This keyword can be followed by a list of user name patterns, separated by spaces. Login is disallowed for user names that match one of the patterns. Only user names are valid; a numerical user ID is not recognized. By default, login is allowed for all users. If the pattern takes the form USER@HOST then USER and HOST are separately checked, restricting logins to particular users from particular hosts. HOST criteria may additionally contain addresses to match in CIDR address/masklen format. The allow/deny users directives are processed in the following order: DenyUsers, AllowUsers. See PATTERNS in ssh_config(5) for more information on patterns. This keyword may appear multiple times in sshd_config with each instance appending to the list.

DisableForwarding

Disables all forwarding features, including X11, ssh-agent(1), TCP and StreamLocal. This option overrides all other forwarding-related options and may simplify restricted configurations.

ExposeAuthInfo

Writes a temporary file containing a list of authentication methods and public credentials (e.g. keys) used to authenticate the user. The location of the file is exposed to the user session through the SSH_USER_AUTH environment variable. The default is no.

FingerprintHash

Specifies the hash algorithm used when logging key fingerprints. Valid options are: md5 and sha256. The default is sha256.

ForceCommand

Forces the execution of the command specified by ForceCommand, ignoring any command supplied by the client and ~/.ssh/rc if present. The command is invoked by using the user's login shell with the -c option. This applies to shell, command, or subsystem execution. It is most useful inside a Match block. The command originally supplied by the client is available in the SSH_ORIGINAL_COMMAND environment variable. Specifying a command of internal-sftp will force the use of an in-process SFTP server that requires no support files when used with ChrootDirectory. The default is none.

GatewayPorts

Specifies whether remote hosts are allowed to connect to ports forwarded for the client. By default, sshd(8) binds remote port forwardings to the loopback address. This prevents other remote hosts from connecting to forwarded ports. GatewayPorts can be used to specify that sshd should allow remote port forwardings to bind to non-loopback addresses, thus allowing other hosts to connect. The argument may be no to force remote port forwardings to be available to the local host only, yes to force remote port forwardings to bind to the wildcard address, or clientspecified to allow the client to select the address to which the forwarding is bound. The default is no.

GSSAPIAuthentication

Specifies whether user authentication based on GSSAPI is allowed. The default is no.

GSSAPICleanupCredentials

Specifies whether to automatically destroy the user's credentials cache on logout. The default is yes.

GSSAPIStrictAcceptorCheck

Determines whether to be strict about the identity of the GSSAPI acceptor a client authenticates against. If set to yes then the client must authenticate against the host service on the current hostname. If set to no then the client may authenticate against any service key stored in the machine's default store. This facility is provided to assist with operation on multi homed machines. The default is yes.

HostbasedAcceptedAlgorithms

Specifies the signature algorithms that will be accepted for hostbased authentication as a list of comma-separated patterns. Alternately if the specified list begins with a ‘+’ character, then the specified signature algorithms will be appended to the default set instead of replacing them. If the specified list begins with a ‘-’ character, then the specified signature algorithms (including wildcards) will be removed from the default set instead of replacing them. If the specified list begins with a ‘^’ character, then the specified signature algorithms will be placed at the head of the default set. The default for this option is the same as for HostKeyAlgorithms option. The list of available signature algorithms may also be obtained using "ssh -Q HostbasedAcceptedAlgorithms". This was formerly named HostbasedAcceptedKeyTypes.

HostbasedAuthentication

Specifies whether rhosts or /etc/hosts.equiv authentication together with successful public key client host authentication is allowed (host-based authentication). The default is no.

HostbasedUsesNameFromPacketOnly

Specifies whether or not the server will attempt to perform a reverse name lookup when matching the name in the ~/.shosts, ~/.rhosts, and /etc/hosts.equiv files during HostbasedAuthentication. A setting of yes means that sshd(8) uses the name supplied by the client rather than attempting to resolve the name from the TCP connection itself. The default is no.

HostCertificate

Specifies a file containing a public host certificate. The certificate's public key must match a private host key already specified by HostKey. The default behaviour of sshd(8) is not to load any certificates.

HostKey

Specifies a file containing a private host key used by SSH. The defaults are /etc/openssh/ssh_host_ecdsa_key, /etc/openssh/ssh_host_ed25519_key and /etc/openssh/ssh_host_rsa_key. Note that sshd(8) will refuse to use a file if it is group/world-accessible and that the HostKeyAlgorithms option restricts which of the keys are actually used by sshd(8).

It is possible to have multiple host key files. It is also possible to specify public host key files instead. In this case operations on the private key will be delegated to an ssh-agent(1).

HostKeyAgent

Identifies the UNIX-domain socket used to communicate with an agent that has access to the private host keys. If the string "SSH_AUTH_SOCK" is specified, the location of the socket will be read from the SSH_AUTH_SOCK environment variable.

HostKeyAlgorithms

Specifies the host key signature algorithms that the server offers. The default for this option is:

```
ssh-ed25519-cert-v01@openssh.com,
ecdsa-sha2-nistp256-cert-v01@openssh.com,
ecdsa-sha2-nistp384-cert-v01@openssh.com,
ecdsa-sha2-nistp521-cert-v01@openssh.com,
sk-ssh-ed25519-cert-v01@openssh.com,
sk-ecdsa-sha2-nistp256-cert-v01@openssh.com,
rsa-sha2-512-cert-v01@openssh.com,
rsa-sha2-256-cert-v01@openssh.com,
ssh-ed25519,
ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
sk-ssh-ed25519@openssh.com,
sk-ecdsa-sha2-nistp256@openssh.com,
rsa-sha2-512,rsa-sha2-256
```

The list of available signature algorithms may also be obtained using "ssh -Q HostKeyAlgorithms".

IgnoreRhosts

Specifies whether to ignore per-user .rhosts and .shosts files during HostbasedAuthentication. The system-wide /etc/hosts.equiv and /etc/openssh/shosts.equiv are still used regardless of this setting. Accepted values are yes (the default) to ignore all per-user files, shosts-only to allow the use of .shosts but to ignore .rhosts or no to allow both .shosts and rhosts.

IgnoreUserKnownHosts

Specifies whether sshd(8) should ignore the user's ~/.ssh/known_hosts during HostbasedAuthentication and use only the system-wide known hosts file /etc/openssh/ssh_known_hosts. The default is “no”.

Include

Include the specified configuration file(s). Multiple pathnames may be specified and each pathname may contain glob(7) wildcards that will be expanded and processed in lexical order. Files without absolute paths are assumed to be in /etc/ssh. An Include directive may appear inside a Match block to perform conditional inclusion.

IPQoS

Specifies the IPv4 type-of-service or DSCP class for the connection. Accepted values are af11, af12, af13, af21, af22, af23, af31, af32, af33, af41, af42, af43, cs0, cs1, cs2, cs3, cs4, cs5, cs6, cs7, ef, le, lowdelay, throughput, reliability, a numeric value, or none to use the operating system default. This option may take one or two arguments, separated by whitespace. If one argument is specified, it is used as the packet class unconditionally. If two values are specified, the first is automatically selected for interactive sessions and the second for non-interactive sessions. The default is af21 (Low-Latency Data) for interactive sessions and cs1 (Lower Effort) for non-interactive sessions.

KbdInteractiveAuthentication

Specifies whether to allow keyboard-interactive authentication. The default is no. The argument to this keyword must be yes or no. ChallengeResponseAuthentication is a deprecated alias for this.

KerberosAuthentication

Specifies whether the password provided by the user for PasswordAuthentication will be validated through the Kerberos KDC. To use this option, the server needs a Kerberos servtab which allows the verification of the KDC's identity. The default is no.

KerberosGetAFSToken

If AFS is active and the user has a Kerberos 5 TGT, attempt to acquire an AFS token before accessing the user's home directory. The default is no.

KerberosOrLocalPasswd

If password authentication through Kerberos fails then the password will be validated via any additional local mechanism such as /etc/passwd. The default is yes.

KerberosTicketCleanup

Specifies whether to automatically destroy the user's ticket cache file on logout. The default is yes.

KexAlgorithms

Specifies the available KEX (Key Exchange) algorithms. Multiple algorithms must be comma-separated. Alternately if the specified list begins with a ‘+’ character, then the specified algorithms will be appended to the default set instead of replacing them. If the specified list begins with a ‘-’ character, then the specified algorithms (including wildcards) will be removed from the default set instead of replacing them. If the specified list begins with a ‘^’ character, then the specified algorithms will be placed at the head of the default set. The supported algorithms are:

- curve25519-sha256

- curve25519-sha256@libssh.org

- diffie-hellman-group1-sha1

- diffie-hellman-group14-sha1

- diffie-hellman-group14-sha256

- diffie-hellman-group16-sha512

- diffie-hellman-group18-sha512

- diffie-hellman-group-exchange-sha1

- diffie-hellman-group-exchange-sha256

- ecdh-sha2-nistp256

- ecdh-sha2-nistp384

- ecdh-sha2-nistp521

- sntrup761x25519-sha512@openssh.com

The default is:

```
sntrup761x25519-sha512@openssh.com,
curve25519-sha256,curve25519-sha256@libssh.org,
ecdh-sha2-nistp521,ecdh-sha2-nistp384,ecdh-sha2-nistp256,
diffie-hellman-group-exchange-sha256,
diffie-hellman-group16-sha512,diffie-hellman-group18-sha512,
diffie-hellman-group14-sha256
```

The list of available key exchange algorithms may also be obtained using "ssh -Q KexAlgorithms".

ListenAddress

Specifies the local addresses sshd(8) should listen on. The following forms may be used:

- ListenAddress hostname|address [rdomain domain]

- ListenAddress hostname:port [rdomain domain]

- ListenAddress IPv4_address:port [rdomain domain]

- ListenAddress [hostname|address]:port [rdomain domain]

The optional rdomain qualifier requests sshd(8) listen in an explicit routing domain. If port is not specified, sshd will listen on the address and all Port options specified. The default is to listen on all local addresses on the current default routing domain. Multiple ListenAddress options are permitted. For more information on routing domains, see rdomain(4).

LoginGraceTime

The server disconnects after this time if the user has not successfully logged in. If the value is 0, there is no time limit. The default is 120 seconds.

LogLevel

Gives the verbosity level that is used when logging messages from sshd(8). The possible values are: QUIET, FATAL, ERROR, INFO, VERBOSE, DEBUG, DEBUG1, DEBUG2, and DEBUG3. The default is INFO. DEBUG and DEBUG1 are equivalent. DEBUG2 and DEBUG3 each specify higher levels of debugging output. Logging with a DEBUG level violates the privacy of users and is not recommended.

LogVerbose

Specify one or more overrides to LogLevel. An override consists of a pattern lists that matches the source file, function and line number to force detailed logging for. For example, an override pattern of:

```
kex.c:*:1000,*:kex_exchange_identification():*,packet.c:*
```

would enable detailed logging for line 1000 of kex.c, everything in the kex_exchange_identification() function, and all code in the packet.c file. This option is intended for debugging and no overrides are enabled by default.

MACs

Specifies the available MAC (message authentication code) algorithms. The MAC algorithm is used for data integrity protection. Multiple algorithms must be comma-separated. If the specified list begins with a ‘+’ character, then the specified algorithms will be appended to the default set instead of replacing them. If the specified list begins with a ‘-’ character, then the specified algorithms (including wildcards) will be removed from the default set instead of replacing them. If the specified list begins with a ‘^’ character, then the specified algorithms will be placed at the head of the default set. The algorithms that contain "-etm" calculate the MAC after encryption (encrypt-then-mac). These are considered safer and their use recommended. The supported MACs are:

- hmac-md5

- hmac-md5-96

- hmac-sha1

- hmac-sha1-96

- hmac-sha2-256

- hmac-sha2-512

- umac-64@openssh.com

- umac-128@openssh.com

- hmac-md5-etm@openssh.com

- hmac-md5-96-etm@openssh.com

- hmac-sha1-etm@openssh.com

- hmac-sha1-96-etm@openssh.com

- hmac-sha2-256-etm@openssh.com

- hmac-sha2-512-etm@openssh.com

- umac-64-etm@openssh.com

- umac-128-etm@openssh.com

The default is:

```
umac-128-etm@openssh.com,umac-64-etm@openssh.com,
hmac-sha2-512-etm@openssh.com,hmac-sha2-256-etm@openssh.com,
hmac-sha1-etm@openssh.com,
umac-128@openssh.com,umac-64@openssh.com,
hmac-sha2-512,hmac-sha2-256,hmac-sha1
```

The list of available MAC algorithms may also be obtained using "ssh -Q mac".

Match

Introduces a conditional block. If all of the criteria on the Match line are satisfied, the keywords on the following lines override those set in the global section of the config file, until either another Match line or the end of the file. If a keyword appears in multiple Match blocks that are satisfied, only the first instance of the keyword is applied. The arguments to Match are one or more criteria-pattern pairs or the single token All which matches all criteria. The available criteria are User, Group, Host, LocalAddress, LocalPort, RDomain, and Address (with RDomain representing the rdomain(4) on which the connection was received).

The match patterns may consist of single entries or comma-separated lists and may use the wildcard and negation operators described in the PATTERNS section of ssh_config(5).

The patterns in an Address criteria may additionally contain addresses to match in CIDR address/masklen format, such as 192.0.2.0/24 or 2001:db8::/32. Note that the mask length provided must be consistent with the address - it is an error to specify a mask length that is too long for the address or one with bits set in this host portion of the address. For example, 192.0.2.0/33 and 192.0.2.0/8, respectively.

Only a subset of keywords may be used on the lines following a Match keyword. Available keywords are AcceptEnv, AllowAgentForwarding, AllowGroups, AllowStreamLocalForwarding, AllowTcpForwarding, AllowUsers, AuthenticationMethods, AuthorizedKeysCommand, AuthorizedKeysCommandUser, AuthorizedKeysFile, AuthorizedPrincipalsCommand, AuthorizedPrincipalsCommandUser, AuthorizedPrincipalsFile, Banner, CASignatureAlgorithms, ChannelTimeout, ChrootDirectory, ClientAliveCountMax, ClientAliveInterval, DenyGroups, DenyUsers, DisableForwarding, ExposeAuthInfo, ForceCommand, GatewayPorts, GSSAPIAuthentication, HostbasedAcceptedAlgorithms, HostbasedAuthentication, HostbasedUsesNameFromPacketOnly, IgnoreRhosts, Include, IPQoS, KbdInteractiveAuthentication, KerberosAuthentication, LogLevel, MaxAuthTries, MaxSessions, PasswordAuthentication, PermitEmptyPasswords, PermitListen, PermitOpen, PermitRootLogin, PermitTTY, PermitTunnel, PermitUserRC, PubkeyAcceptedAlgorithms, PubkeyAuthentication, PubkeyAuthOptions, RekeyLimit, RevokedKeys, RDomain, SetEnv, StreamLocalBindMask, StreamLocalBindUnlink, TrustedUserCAKeys, UnusedConnectionTimeout, X11DisplayOffset, X11Forwarding and X11UseLocalhost.

MaxAuthTries

Specifies the maximum number of authentication attempts permitted per connection. Once the number of failures reaches half this value, additional failures are logged. The default is 6.

MaxSessions

Specifies the maximum number of open shell, login or subsystem (e.g. sftp) sessions permitted per network connection. Multiple sessions may be established by clients that support connection multiplexing. Setting MaxSessions to 1 will effectively disable session multiplexing, whereas setting it to 0 will prevent all shell, login and subsystem sessions while still permitting forwarding. The default is 10.

MaxStartups

Specifies the maximum number of concurrent unauthenticated connections to the SSH daemon. Additional connections will be dropped until authentication succeeds or the LoginGraceTime expires for a connection. The default is 10:30:100. Alternatively, random early drop can be enabled by specifying the three colon separated values start:rate:full (e.g. "10:30:60"). sshd(8) will refuse connection attempts with a probability of rate/100 (30%) if there are currently start (10) unauthenticated connections. The probability increases linearly and all connection attempts are refused if the number of unauthenticated connections reaches full (60).

ModuliFile

Specifies the moduli(5) file that contains the Diffie-Hellman groups used for the “diffie-hellman-group-exchange-sha1” and “diffie-hellman-group-exchange-sha256” key exchange methods. The default is /etc/openssh/moduli.

PasswordAuthentication

Specifies whether password authentication is allowed. The default is yes.

PermitEmptyPasswords

When password authentication is allowed, it specifies whether the server allows login to accounts with empty password strings. The default is no.

PermitListen

Specifies the addresses/ports on which a remote TCP port forwarding may listen. The listen specification must be one of the following forms:

- PermitListen port

- PermitListen host:port

Multiple permissions may be specified by separating them with whitespace. An argument of any can be used to remove all restrictions and permit any listen requests. An argument of none can be used to prohibit all listen requests. The host name may contain wildcards as described in the PATTERNS section in ssh_config(5). The wildcard ‘*’ can also be used in place of a port number to allow all ports. By default all port forwarding listen requests are permitted. Note that the GatewayPorts option may further restrict which addresses may be listened on. Note also that ssh(1) will request a listen host of “localhost” if no listen host was specifically requested, and this name is treated differently to explicit localhost addresses of “127.0.0.1” and “::1”.

PermitOpen

Specifies the destinations to which TCP port forwarding is permitted. The forwarding specification must be one of the following forms:

- PermitOpen host:port

- PermitOpen IPv4_addr:port

- PermitOpen [IPv6_addr]:port

Multiple forwards may be specified by separating them with whitespace. An argument of any can be used to remove all restrictions and permit any forwarding requests. An argument of none can be used to prohibit all forwarding requests. The wildcard ‘*’ can be used for host or port to allow all hosts or ports respectively. Otherwise, no pattern matching or address lookups are performed on supplied names. By default all port forwarding requests are permitted.

PermitRootLogin

Specifies whether root can log in using ssh(1). The argument must be yes, prohibit-password, forced-commands-only, or no. The default is without-password. If this option is set to prohibit-password (or its deprecated alias, without-password), password and keyboard-interactive authentication are disabled for root.

If this option is set to forced-commands-only, root login with public key authentication will be allowed, but only if the command option has been specified (which may be useful for taking remote backups even if root login is normally not allowed). All other authentication methods are disabled for root.

If this option is set to no, root is not allowed to log in.

PermitTTY

Specifies whether pty(4) allocation is permitted. The default is yes.

PermitTunnel

Specifies whether tun(4) device forwarding is allowed. The argument must be yes, point-to-point (layer 3), ethernet (layer 2), or no. Specifying yes permits both point-to-point and ethernet. The default is no. Independent of this setting, the permissions of the selected tun(4) device must allow access to the user.

PermitUserEnvironment

Specifies whether ~/.ssh/environment and environment= options in ~/.ssh/authorized_keys and /etc/openssh/authorized_keys/ are processed by sshd(8). Valid options are yes, no or a pattern-list specifying which environment variable names to accept (for example "LANG,LC_*"). The default is no. Enabling environment processing may enable users to bypass access restrictions in some configurations using mechanisms such as LD_PRELOAD.

PermitUserRC

Specifies whether any ~/.ssh/rc file is executed. The default is yes.

PerSourceMaxStartups

Specifies the number of unauthenticated connections allowed from a given source address, or “none” if there is no limit. This limit is applied in addition to MaxStartups, whichever is lower. The default is none.

PerSourceNetBlockSize

Specifies the number of bits of source address that are grouped together for the purposes of applying PerSourceMaxStartups limits. Values for IPv4 and optionally IPv6 may be specified, separated by a colon. The default is 32:128, which means each address is considered individually.

PidFile

Specifies the file that contains the process ID of the SSH daemon, or none to not write one. The default is /var/run/sshd.pid.

Port

Specifies the port number that sshd(8) listens on. The default is 22. Multiple options of this type are permitted. See also ListenAddress.

PrintLastLog

Specifies whether sshd(8) should print the date and time of the last user login when a user logs in interactively. The default is yes.

PrintMotd

Specifies whether sshd(8) should print /etc/motd when a user logs in interactively. (On some systems it is also printed by the shell, /etc/profile, or equivalent.) The default is yes.

PubkeyAcceptedAlgorithms

Specifies the signature algorithms that will be accepted for public key authentication as a list of comma-separated patterns. Alternately if the specified list begins with a ‘+’ character, then the specified algorithms will be appended to the default set instead of replacing them. If the specified list begins with a ‘-’ character, then the specified algorithms (including wildcards) will be removed from the default set instead of replacing them. If the specified list begins with a ‘^’ character, then the specified algorithms will be placed at the head of the default set. The default for this option is the same as for HostKeyAlgorithms option. The list of available signature algorithms may also be obtained using "ssh -Q PubkeyAcceptedAlgorithms".

PubkeyAuthOptions

Sets one or more public key authentication options. The supported keywords are: none (the default; indicating no additional options are enabled), touch-required and verify-required. The touch-required option causes public key authentication using a FIDO authenticator algorithm (i.e. ecdsa-sk or ed25519-sk) to always require the signature to attest that a physically present user explicitly confirmed the authentication (usually by touching the authenticator). By default, sshd(8) requires user presence unless overridden with an authorized_keys option. The touch-required flag disables this override.

The verify-required option requires a FIDO key signature attest that the user was verified, e.g. via a PIN.

Neither the touch-required or verify-required options have any effect for other, non-FIDO, public key types.

PubkeyAuthentication

Specifies whether public key authentication is allowed. The default is yes.

RekeyLimit

Specifies the maximum amount of data that may be transmitted or received before the session key is renegotiated, optionally followed by a maximum amount of time that may pass before the session key is renegotiated. The first argument is specified in bytes and may have a suffix of ‘K’, ‘M’, or ‘G’ to indicate Kilobytes, Megabytes, or Gigabytes, respectively. The default is between ‘1G’ and ‘4G’, depending on the cipher. The optional second value is specified in seconds and may use any of the units documented in the TIME FORMATS section. The default value for RekeyLimit is default none, which means that rekeying is performed after the cipher's default amount of data has been sent or received and no time based rekeying is done.

RequiredRSASize

Specifies the minimum RSA key size (in bits) that sshd(8) will accept. User and host-based authentication keys smaller than this limit will be refused. The default is 1024 bits. Note that this limit may only be raised from the default.

RevokedKeys

Specifies revoked public keys file, or none to not use one. Keys listed in this file will be refused for public key authentication. Note that if this file is not readable, then public key authentication will be refused for all users. Keys may be specified as a text file, listing one public key per line, or as an OpenSSH Key Revocation List (KRL) as generated by ssh-keygen(1). For more information on KRLs, see the KEY REVOCATION LISTS section in ssh-keygen(1).

RDomain

Specifies an explicit routing domain that is applied after authentication has completed. The user session, as well as any forwarded or listening IP sockets, will be bound to this rdomain(4). If the routing domain is set to %D, then the domain in which the incoming connection was received will be applied.

SecurityKeyProvider

Specifies a path to a library that will be used when loading FIDO authenticator-hosted keys, overriding the default of using the built-in USB HID support.

SetEnv

Specifies one or more environment variables to set in child sessions started by sshd(8) as “NAME=VALUE”. The environment value may be quoted (e.g. if it contains whitespace characters). Environment variables set by SetEnv override the default environment and any variables specified by the user via AcceptEnv or PermitUserEnvironment.

StreamLocalBindMask

Sets the octal file creation mode mask (umask) used when creating a Unix-domain socket file for local or remote port forwarding. This option is only used for port forwarding to a Unix-domain socket file. The default value is 0177, which creates a Unix-domain socket file that is readable and writable only by the owner. Note that not all operating systems honor the file mode on Unix-domain socket files.

StreamLocalBindUnlink

Specifies whether to remove an existing Unix-domain socket file for local or remote port forwarding before creating a new one. If the socket file already exists and StreamLocalBindUnlink is not enabled, sshd will be unable to forward the port to the Unix-domain socket file. This option is only used for port forwarding to a Unix-domain socket file. The argument must be yes or no. The default is no.

StrictModes

Specifies whether sshd(8) should check file modes and ownership of the user's files and home directory before accepting login. This is normally desirable because novices sometimes accidentally leave their directory or files world-writable. The default is yes. Note that this does not apply to ChrootDirectory, whose permissions and ownership are checked unconditionally.

Subsystem

Configures an external subsystem (e.g. file transfer daemon). Arguments should be a subsystem name and a command (with optional arguments) to execute upon subsystem request. The command sftp-server implements the SFTP file transfer subsystem.

Alternately the name internal-sftp implements an in-process SFTP server. This may simplify configurations using ChrootDirectory to force a different filesystem root on clients.

By default no subsystems are defined.

SyslogFacility

Gives the facility code that is used when logging messages from sshd(8). The possible values are: DAEMON, USER, AUTH, AUTHPRIV, LOCAL0, LOCAL1, LOCAL2, LOCAL3, LOCAL4, LOCAL5, LOCAL6, LOCAL7. The default is AUTHPRIV.

TCPKeepAlive

Specifies whether the system should send TCP keepalive messages to the other side. If they are sent, death of the connection or crash of one of the machines will be properly noticed. However, this means that connections will die if the route is down temporarily, and some people find it annoying. On the other hand, if TCP keepalives are not sent, sessions may hang indefinitely on the server, leaving "ghost" users and consuming server resources. The default is yes (to send TCP keepalive messages), and the server will notice if the network goes down or the client host crashes. This avoids infinitely hanging sessions.

To disable TCP keepalive messages, the value should be set to no.

TrustedUserCAKeys

Specifies a file containing public keys of certificate authorities that are trusted to sign user certificates for authentication, or none to not use one. Keys are listed one per line; empty lines and comments starting with ‘#’ are allowed. If a certificate is presented for authentication and has its signing CA key listed in this file, then it may be used for authentication for any user listed in the certificate's principals list. Note that certificates that lack a list of principals will not be permitted for authentication using TrustedUserCAKeys. For more details on certificates, see the CERTIFICATES section in ssh-keygen(1).

UnusedConnectionTimeout

Specifies whether and how quickly sshd(8) should close client connections with no open channels. Open channels include active shell, command execution or subsystem sessions, connected network, socket, agent or X11 forwardings. Forwarding listeners, such as those from the ssh(1) -R flag, are not considered as open channels and do not prevent the timeout. The timeout value is specified in seconds or may use any of the units documented in the TIME FORMATS section. Note that this timeout starts when the client connection completes user authentication but before the client has an opportunity to open any channels. Caution should be used when using short timeout values, as they may not provide sufficient time for the client to request and open its channels before terminating the connection.

The default none is to never expire connections for having no open channels. This option may be useful in conjunction with ChannelTimeout.

UseDNS

Specifies whether sshd(8) should look up the remote host name, and to check that the resolved host name for the remote IP address maps back to the very same IP address. If this option is set to no (the default) then only addresses and not host names may be used in ~/.ssh/authorized_keys from and sshd_config Match Host directives.

UsePAM

Enables the Pluggable Authentication Module interface. If set to yes this will enable PAM authentication using KbdInteractiveAuthentication and PasswordAuthentication in addition to PAM account and session module processing for all authentication types. Because PAM keyboard-interactive authentication usually serves an equivalent role to password authentication, you should disable either PasswordAuthentication or KbdInteractiveAuthentication.

If UsePAM is enabled, you will not be able to run sshd(8) as a non-root user. The default is yes.

VersionAddendum

Optionally specifies additional text to append to the SSH protocol banner sent by the server upon connection. The default is none.

X11DisplayOffset

Specifies the first display number available for sshd(8)'s X11 forwarding. This prevents sshd from interfering with real X11 servers. The default is 10.

X11Forwarding

Specifies whether X11 forwarding is permitted. The argument must be yes or no. The default is yes. When X11 forwarding is enabled, there may be additional exposure to the server and to client displays if the sshd(8) proxy display is configured to listen on the wildcard address (see X11UseLocalhost), though this is not the default. Additionally, the authentication spoofing and authentication data verification and substitution occur on the client side. The security risk of using X11 forwarding is that the client's X11 display server may be exposed to attack when the SSH client requests forwarding (see the warnings for ForwardX11 in ssh_config(5)). A system administrator may have a stance in which they want to protect clients that may expose themselves to attack by unwittingly requesting X11 forwarding, which can warrant a no setting.

Note that disabling X11 forwarding does not prevent users from forwarding X11 traffic, as users can always install their own forwarders.

X11UseLocalhost

Specifies whether sshd(8) should bind the X11 forwarding server to the loopback address or to the wildcard address. By default, sshd binds the forwarding server to the loopback address and sets the hostname part of the DISPLAY environment variable to localhost. This prevents remote hosts from connecting to the proxy display. However, some older X11 clients may not function with this configuration. X11UseLocalhost may be set to no to specify that the forwarding server should be bound to the wildcard address. The argument must be yes or no. The default is yes.

XAuthLocation

Specifies the full pathname of the xauth(1) program, or none to not use one. The default is /usr/bin/xauth.

## TIME FORMATS
sshd(8) command-line arguments and configuration file options that specify time may be expressed using a sequence of the form: time[qualifier], where time is a positive integer value and qualifier is one of the following:

⟨none⟩

seconds

s | S

seconds

m | M

minutes

h | H

hours

d | D

days

w | W

weeks

Each member of the sequence is added together to calculate the total time value.

Time format examples:

600

600 seconds (10 minutes)

10m

10 minutes

1h30m

1 hour 30 minutes (90 minutes)

## TOKENS
Arguments to some keywords can make use of tokens, which are expanded at runtime:

%%

A literal ‘%’.

%C

Identifies the connection endpoints, containing four space-separated values: client address, client port number, server address, and server port number.

%D

The routing domain in which the incoming connection was received.

%F

The fingerprint of the CA key.

%f

The fingerprint of the key or certificate.

%h

The home directory of the user.

%i

The key ID in the certificate.

%K

The base64-encoded CA key.

%k

The base64-encoded key or certificate for authentication.

%s

The serial number of the certificate.

%T

The type of the CA key.

%t

The key or certificate type.

%U

The numeric user ID of the target user.

%u

The username.

AuthorizedKeysCommand accepts the tokens %%, %C, %D, %f, %h, %k, %t, %U, and %u.

AuthorizedKeysFile accepts the tokens %%, %h, %U, and %u.

AuthorizedPrincipalsCommand accepts the tokens %%, %C, %D, %F, %f, %h, %i, %K, %k, %s, %T, %t, %U, and %u.

AuthorizedPrincipalsFile accepts the tokens %%, %h, %U, and %u.

ChrootDirectory accepts the tokens %%, %h, %U, and %u.

RoutingDomain accepts the token %D.

## FILES
/etc/openssh/sshd_config

Contains configuration data for sshd(8). This file should be writable by root only, but it is recommended (though not necessary) that it be world-readable.

## SEE ALSO
sftp-server(8), sshd(8)

## AUTHORS
OpenSSH is a derivative of the original and free ssh 1.2.12 release by Tatu Ylonen. Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, Theo de Raadt and Dug Song removed many bugs, re-added newer features and created OpenSSH. Markus Friedl contributed the support for SSH protocol versions 1.5 and 2.0. Niels Provos and Markus Friedl contributed support for privilege separation.


config

package: openssl

title: config(5ossl)

text:
# config(5ossl)

## NAME
config - OpenSSL CONF library configuration files

## DESCRIPTION
This page documents the syntax of OpenSSL configuration files, as parsed by NCONF_load(3) and related functions. This format is used by many of the OpenSSL commands, and to initialize the libraries when used by any application.

The first part describes the general syntax of the configuration files, and subsequent sections describe the semantics of individual modules. Other modules are described in fips_config(5) and x509v3_config(5). The syntax for defining ASN.1 values is described in ASN1_generate_nconf(3).

## SYNTAX
A configuration file is a series of lines. Blank lines, and whitespace between the elements of a line, have no significance. A comment starts with a # character; the rest of the line is ignored. If the # is the first non-space character in a line, the entire line is ignored.

### Directives
Two directives can be used to control the parsing of configuration files: .include and .pragma.

For compatibility with older versions of OpenSSL, an equal sign after the directive will be ignored. Older versions will treat it as an assignment, so care should be taken if the difference in semantics is important.

A file can include other files using the include syntax:

```
  .include [=] pathname
```

If pathname is a simple filename, that file is included directly at that point. Included files can have .include statements that specify other files. If pathname is a directory, all files within that directory that have a ".cnf" or ".conf" extension will be included. (This is only available on systems with POSIX IO support.) Any sub-directories found inside the pathname are ignored. Similarly, if a file is opened while scanning a directory, and that file has an .include directive that specifies a directory, that is also ignored.

As a general rule, the pathname should be an absolute path; this can be enforced with the abspath and includedir pragmas, described below. The environment variable OPENSSL_CONF_INCLUDE, if it exists, is prepended to all relative pathnames. If the pathname is still relative, it is interpreted based on the current working directory.

To require all file inclusions to name absolute paths, use the following directive:

```
 .pragma [=] abspath:value
```

The default behavior, where the value is false or off, is to allow relative paths. To require all .include pathnames to be absolute paths, use a value of true or on.

In these files, the dollar sign, $, is used to reference a variable, as described below. On some platforms, however, it is common to treat $ as a regular character in symbol names. Supporting this behavior can be done with the following directive:

```
 .pragma [=] dollarid:value
```

The default behavior, where the value is false or off, is to treat the dollarsign as indicating a variable name; "foo$bar" is interpreted as "foo" followed by the expansion of the variable "bar". If value is true or on, then "foo$bar" is a single seven-character name and variable expansions must be specified using braces or parentheses.

```
 .pragma [=] includedir:value
```

If a relative pathname is specified in the .include directive, and the OPENSSL_CONF_INCLUDE environment variable doesn't exist, then the value of the includedir pragma, if it exists, is prepended to the pathname.

### Settings
A configuration file is divided into a number of sections. A section begins with the section name in square brackets, and ends when a new section starts, or at the end of the file. The section name can consist of alphanumeric characters and underscores. Whitespace between the name and the brackets is removed.

The first section of a configuration file is special and is referred to as the default section. This section is usually unnamed and spans from the start of file until the first named section. When a name is being looked up, it is first looked up in the current or named section, and then the default section if necessary.

The environment is mapped onto a section called ENV.

Within a section are a series of name/value assignments, described in more detail below. As a reminder, the square brackets shown in this example are required, not optional:

```
 [ section ]
 name1 = This is value1
 name2 = Another value
 ...
 [ newsection ]
 name1 = New value1
 name3 = Value 3
```

The name can contain any alphanumeric characters as well as a few punctuation symbols such as . , ; and _. Whitespace after the name and before the equal sign is ignored.

If a name is repeated in the same section, then all but the last value are ignored. In certain circumstances, such as with Certificate DNs, the same field may occur multiple times. In order to support this, commands like openssl-req(1) ignore any leading text that is preceded with a period. For example:

```
 1.OU = First OU
 2.OU = Second OU
```

The value consists of the string following the = character until end of line with any leading and trailing whitespace removed.

The value string undergoes variable expansion. The text $var or "${var}" inserts the value of the named variable from the current section. To use a value from another section use $section::name or "${section::name}". By using $ENV::name, the value of the specified environment variable will be substituted.

Variables must be defined before their value is referenced, otherwise an error is flagged and the file will not load. This can be worked around by specifying a default value in the default section before the variable is used.

Any name/value settings in an ENV section are available to the configuration file, but are not propagated to the environment.

It is an error if the value ends up longer than 64k.

It is possible to escape certain characters by using a single ' or double " quote around the value, or using a backslash \ before the character, By making the last character of a line a \ a value string can be spread across multiple lines. In addition the sequences \n, \r, \b and \t are recognized.

The expansion and escape rules as described above that apply to value also apply to the pathname of the .include directive.

## OPENSSL LIBRARY CONFIGURATION
The sections below use the informal term module to refer to a part of the OpenSSL functionality. This is not the same as the formal term FIPS module, for example.

The OpenSSL configuration looks up the value of openssl_conf in the default section and takes that as the name of a section that specifies how to configure any modules in the library. It is not an error to leave any module in its default configuration. An application can specify a different name by calling CONF_modules_load_file(), for example, directly.

OpenSSL also looks up the value of config_diagnostics. If this exists and has a nonzero numeric value, any error suppressing flags passed to CONF_modules_load() will be ignored. This is useful for diagnosing misconfigurations but its use in production requires additional consideration. With this option enabled, a configuration error will completely prevent access to a service. Without this option and in the presence of a configuration error, access will be allowed but the desired configuration will not be used.

```
 # These must be in the default section
 config_diagnostics = 1
 openssl_conf = openssl_init
 [openssl_init]
 oid_section = oids
 providers = providers
 alg_section = evp_properties
 ssl_conf = ssl_configuration
 engines = engines
 random = random
 [oids]
 ... new oids here ...
 [providers]
 ... provider stuff here ...
 [evp_properties]
 ... EVP properties here ...
 [ssl_configuration]
 ... SSL/TLS configuration properties here ...
 [engines]
 ... engine properties here ...
 [random]
 ... random properties here ...
```

The semantics of each module are described below. The phrase "in the initialization section" refers to the section identified by the openssl_conf or other name (given as openssl_init in the example above). The examples below assume the configuration above is used to specify the individual sections.

### ASN.1 Object Identifier Configuration
The name oid_section in the initialization section names the section containing name/value pairs of OID's. The name is the short name; the value is an optional long name followed by a comma, and the numeric value. While some OpenSSL commands have their own section for specifying OID's, this section makes them available to all commands and applications.

```
 [oids]
 shortName = a very long OID name, 1.2.3.4
 newoid1 = 1.2.3.4.1
 some_other_oid = 1.2.3.5
```

If a full configuration with the above fragment is in the file example.cnf, then the following command line:

```
 OPENSSL_CONF=example.cnf openssl asn1parse -genstr OID:1.2.3.4.1
```

will output:

```
 0:d=0  hl=2 l=   4 prim: OBJECT            :newoid1
```

showing that the OID "newoid1" has been added as "1.2.3.4.1".

### Provider Configuration
The name providers in the initialization section names the section containing cryptographic provider configuration. The name/value assignments in this section each name a provider, and point to the configuration section for that provider. The provider-specific section is used to specify how to load the module, activate it, and set other parameters.

Within a provider section, the following names have meaning:

identity

This is used to specify an alternate name, overriding the default name specified in the list of providers. For example:

```
 [providers]
 foo = foo_provider
 [foo_provider]
 identity = my_fips_module

```

module

Specifies the pathname of the module (typically a shared library) to load.

activate

If present and set to one of the values yes, on, true or 1, then the associated provider will be activated. Conversely, setting this value to no, off, false, or 0 will prevent the provider from being activated. Settings can be given in lower or uppercase. Setting activate to any other setting, or omitting a setting value will result in an error. = item soft_load

If enabled, informs the library to clear the error stack on failure to activate requested provider. A value of 1, yes, true or on (in lower or uppercase) will activate this setting, while a value of 0, no, false, or off (again in lower or uppercase) will disable this setting. Any other value will produce an error. Note this setting defaults to off if not provided

All parameters in the section as well as sub-sections are made available to the provider.

Default provider and its activation

If no providers are activated explicitly, the default one is activated implicitly. See OSSL_PROVIDER-default(7) for more details.

If you add a section explicitly activating any other provider(s), you most probably need to explicitly activate the default provider, otherwise it becomes unavailable in openssl. It may make the system remotely unavailable.

### EVP Configuration
The name alg_section in the initialization section names the section containing algorithmic properties when using the EVP API.

Within the algorithm properties section, the following names have meaning:

default_properties

The value may be anything that is acceptable as a property query string for EVP_set_default_properties().

fips_mode (deprecated)

The value is a boolean that can be yes or no. If the value is yes, this is exactly equivalent to:

```
 default_properties = fips=yes

```

If the value is no, nothing happens. Using this name is deprecated, and if used, it must be the only name in the section.

### SSL Configuration
The name ssl_conf in the initialization section names the section containing the list of SSL/TLS configurations. As with the providers, each name in this section identifies a section with the configuration for that name. For example:

```
 [ssl_configuration]
 server = server_tls_config
 client = client_tls_config
 system_default = tls_system_default
 [server_tls_config]
 ... configuration for SSL/TLS servers ...
 [client_tls_config]
 ... configuration for SSL/TLS clients ...
```

The configuration name system_default has a special meaning. If it exists, it is applied whenever an SSL_CTX object is created. For example, to impose system-wide minimum TLS and DTLS protocol versions:

```
 [tls_system_default]
 MinProtocol = TLSv1.2
 MinProtocol = DTLSv1.2
```

The minimum TLS protocol is applied to SSL_CTX objects that are TLS-based, and the minimum DTLS protocol to those are DTLS-based. The same applies also to maximum versions set with MaxProtocol.

Each configuration section consists of name/value pairs that are parsed by SSL_CONF_cmd(3), which will be called by SSL_CTX_config() or SSL_config(), appropriately. Note that any characters before an initial dot in the configuration section are ignored, so that the same command can be used multiple times. This probably is most useful for loading different key types, as shown here:

```
 [server_tls_config]
 RSA.Certificate = server-rsa.pem
 ECDSA.Certificate = server-ecdsa.pem
```

### Engine Configuration
The name engines in the initialization section names the section containing the list of ENGINE configurations. As with the providers, each name in this section identifies an engine with the configuration for that engine. The engine-specific section is used to specify how to load the engine, activate it, and set other parameters.

Within an engine section, the following names have meaning:

engine_id

This is used to specify an alternate name, overriding the default name specified in the list of engines. If present, it must be first. For example:

```
 [engines]
 foo = foo_engine
 [foo_engine]
 engine_id = myfoo

```

dynamic_path

This loads and adds an ENGINE from the given path. It is equivalent to sending the ctrls SO_PATH with the path argument followed by LIST_ADD with value 2 and LOAD to the dynamic ENGINE. If this is not the required behaviour then alternative ctrls can be sent directly to the dynamic ENGINE using ctrl commands.

init

This specifies whether to initialize the ENGINE. If the value is 0 the ENGINE will not be initialized, if the value is 1 an attempt is made to initialize the ENGINE immediately. If the init command is not present then an attempt will be made to initialize the ENGINE after all commands in its section have been processed.

default_algorithms

This sets the default algorithms an ENGINE will supply using the function ENGINE_set_default_string().

All other names are taken to be the name of a ctrl command that is sent to the ENGINE, and the value is the argument passed with the command. The special value EMPTY means no value is sent with the command. For example:

```
 [engines]
 foo = foo_engine
 [foo_engine]
 dynamic_path = /some/path/fooengine.so
 some_ctrl = some_value
 default_algorithms = ALL
 other_ctrl = EMPTY
```

### Random Configuration
The name random in the initialization section names the section containing the random number generator settings.

Within the random section, the following names have meaning:

random

This is used to specify the random bit generator. For example:

```
 [random]
 random = CTR-DRBG

```

The available random bit generators are:

CTR-DRBG

HASH-DRBG

HMAC-DRBG

cipher

This specifies what cipher a CTR-DRBG random bit generator will use. Other random bit generators ignore this name. The default value is AES-256-CTR.

digest

This specifies what digest the HASH-DRBG or HMAC-DRBG random bit generators will use. Other random bit generators ignore this name.

properties

This sets the property query used when fetching the random bit generator and any underlying algorithms.

seed

This sets the randomness source that should be used. By default SEED-SRC will be used outside of the FIPS provider. The FIPS provider uses call backs to access the same randomness sources from outside the validated boundary.

seed_properties

This sets the property query used when fetching the randomness source.

random_provider

This sets the provider to use for the RAND_bytes(3) calls instead of the built-in entropy sources. It defaults to "fips". If the named provider is not loaded, the built-in entropy sources will be used.

## EXAMPLES
This example shows how to use quoting and escaping.

```
 # This is the default section.
 HOME = /temp
 configdir = $ENV::HOME/config
 [ section_one ]
 # Quotes permit leading and trailing whitespace
 any = " any variable name "
 other = A string that can \
 cover several lines \
 by including \\ characters
 message = Hello World\n
 [ section_two ]
 greeting = $section_one::message
```

This example shows how to expand environment variables safely. In this example, the variable tempfile is intended to refer to a temporary file, and the environment variable TEMP or TMP, if present, specify the directory where the file should be put. Since the default section is checked if a variable does not exist, it is possible to set TMP to default to /tmp, and TEMP to default to TMP.

```
 # These two lines must be in the default section.
 TMP = /tmp
 TEMP = $ENV::TMP
 # This can be used anywhere
 tmpfile = ${ENV::TEMP}/tmp.filename
```

This example shows how to enforce FIPS mode for the application sample.

```
 sample = fips_config
 [fips_config]
 alg_section = evp_properties
 [evp_properties]
 default_properties = "fips=yes"
```

## ENVIRONMENT
OPENSSL_CONF

The path to the config file, or the empty string for none. Ignored in set-user-ID and set-group-ID programs.

OPENSSL_ENGINES

The path to the engines directory. Ignored in set-user-ID and set-group-ID programs.

OPENSSL_MODULES

The path to the directory with OpenSSL modules, such as providers. Ignored in set-user-ID and set-group-ID programs.

OPENSSL_CONF_INCLUDE

The optional path to prepend to all .include paths.

## BUGS
There is no way to include characters using the octal \nnn form. Strings are all null terminated so nulls cannot form part of the value.

The escaping isn't quite right: if you want to use sequences like \n you can't use any quote escaping on the same line.

The limit that only one directory can be opened and read at a time can be considered a bug and should be fixed.

## HISTORY
An undocumented API, NCONF_WIN32(), used a slightly different set of parsing rules there were intended to be tailored to the Microsoft Windows platform. Specifically, the backslash character was not an escape character and could be used in pathnames, only the double-quote character was recognized, and comments began with a semi-colon. This function was deprecated in OpenSSL 3.0; applications with configuration files using that syntax will have to be modified.

## SEE ALSO
openssl-x509(1), openssl-req(1), openssl-ca(1), openssl-fipsinstall(1), ASN1_generate_nconf(3), EVP_set_default_properties(3), CONF_modules_load(3), CONF_modules_load_file(3), RAND_bytes(3), fips_config(5), and x509v3_config(5).

## COPYRIGHT
Copyright 2000-2025 The OpenSSL Project Authors. All Rights Reserved.

Licensed under the Apache License 2.0 (the "License"). You may not use this file except in compliance with the License. You can obtain a copy in the file LICENSE in the source distribution or at <https://www.openssl.org/source/license.html>.

branch: sisyphus


title: fips_config(5ossl)

summary: OpenSSL FIPS configuration

text:
# fips_config(5ossl)

## NAME
fips_config - OpenSSL FIPS configuration

## DESCRIPTION
A separate configuration file, using the OpenSSL config(5) syntax, is used to hold information about the FIPS module. This includes a digest of the shared library file, and status about the self-testing. This data is used automatically by the module itself for two purposes:

- Run the startup FIPS self-test known answer tests (KATS).

This is normally done once, at installation time, but may also be set up to run each time the module is used.

- Verify the module's checksum.

This is done each time the module is used.

This file is generated by the openssl-fipsinstall(1) program, and used internally by the FIPS module during its initialization.

The following options are supported. They should all appear in a section whose name is identified by the fips option in the providers section, as described in "Provider Configuration Module" in config(5).

activate

If present, the module is activated. The value assigned to this name is not significant.

conditional-errors

The FIPS module normally enters an internal error mode if any self test fails. Once this error mode is active, no services or cryptographic algorithms are accessible from this point on. Continuous tests are a subset of the self tests (e.g., a key pair test during key generation, or the CRNG output test). Setting this value to 0 allows the error mode to not be triggered if any continuous test fails. The default value of 1 will trigger the error mode. Regardless of the value, the operation (e.g., key generation) that called the continuous test will return an error code if its continuous test fails. The operation may then be retried if the error mode has not been triggered.

module-mac

The calculated MAC of the FIPS provider file.

install-version

A version number for the fips install process. Should be 1.

install-status

This field is deprecated and is no longer used.

install-mac

This field is deprecated and is no longer used.

### FIPS indicator options
The following FIPS configuration options indicate if run-time checks related to enforcement of FIPS security parameters such as minimum security strength of keys and approved curve names are used. A value of '1' will perform the checks, otherwise if the value is '0' the checks are not performed and FIPS compliance must be done by procedures documented in the relevant Security Policy.

See "OPTIONS" in openssl-fipsinstall(1) for further information related to these options.

security-checks

See "OPTIONS" in openssl-fipsinstall(1) -no_security_checks

tls1-prf-ems-check

See "OPTIONS" in openssl-fipsinstall(1) -ems_check

no-short-mac

See "OPTIONS" in openssl-fipsinstall(1) -no_short_mac

drbg-no-trunc-md

See "OPTIONS" in openssl-fipsinstall(1) -no_drbg_truncated_digests

signature-digest-check

See "OPTIONS" in openssl-fipsinstall(1) -signature_digest_check

hkdf-digest-check

This option is deprecated.

tls13-kdf-digest-check

See "OPTIONS" in openssl-fipsinstall(1) -tls13_kdf_digest_check

tls1-prf-digest-check

See "OPTIONS" in openssl-fipsinstall(1) -tls1_prf_digest_check

sshkdf-digest-check

See "OPTIONS" in openssl-fipsinstall(1) -sshkdf_digest_check

sskdf-digest-check

This option is deprecated.

x963kdf-digest-check

See "OPTIONS" in openssl-fipsinstall(1) -x963kdf_digest_check

dsa-sign-disabled

See "OPTIONS" in openssl-fipsinstall(1) -dsa_sign_disabled

tdes-encrypt-disabled

See "OPTIONS" in openssl-fipsinstall(1) -tdes_encrypt_disabled

rsa-pkcs15-pad-disabled

See "OPTIONS" in openssl-fipsinstall(1) -rsa_pkcs15_pad_disabled

rsa-pss-saltlen-check

See "OPTIONS" in openssl-fipsinstall(1) -rsa_pss_saltlen_check

rsa-sign-x931-pad-disabled

See "OPTIONS" in openssl-fipsinstall(1) -rsa_sign_x931_disabled

hkdf-key-check

See "OPTIONS" in openssl-fipsinstall(1) -hkdf_key_check

kbkdf-key-check

See "OPTIONS" in openssl-fipsinstall(1) -kbkdf_key_check

tls13-kdf-key-check

See "OPTIONS" in openssl-fipsinstall(1) -tls13_kdf_key_check

tls1-prf-key-check

See "OPTIONS" in openssl-fipsinstall(1) -tls1_prf_key_check

sshkdf-key-check

See "OPTIONS" in openssl-fipsinstall(1) -sshkdf_key_check

sskdf-key-check

See "OPTIONS" in openssl-fipsinstall(1) -sskdf_key_check

x963kdf-key-check

See "OPTIONS" in openssl-fipsinstall(1) -x963kdf_key_check

x942kdf-key-check

See "OPTIONS" in openssl-fipsinstall(1) -x942kdf_key_check

pbkdf2-lower-bound-check

See "OPTIONS" in openssl-fipsinstall(1) -no_pbkdf2_lower_bound_check

ecdh-cofactor-check

See "OPTIONS" in openssl-fipsinstall(1) -ecdh_cofactor_check

hmac-key-check

See "OPTIONS" in openssl-fipsinstall(1) -hmac_key_check

kmac-key-check

See "OPTIONS" in openssl-fipsinstall(1) -kmac_key_check

For example:

```
 [fips_sect]
 activate = 1
 install-version = 1
 conditional-errors = 1
 security-checks = 1
 module-mac = 41:D0:FA:C2:5D:41:75:CD:7D:C3:90:55:6F:A4:DC
 install-mac = FE:10:13:5A:D3:B4:C7:82:1B:1E:17:4C:AC:84:0C
 install-status = INSTALL_SELF_TEST_KATS_RUN
```

## NOTES
When using the FIPS provider, it is recommended that the config_diagnostics option is enabled to prevent accidental use of non-FIPS validated algorithms via broken or mistaken configuration. See config(5).

## SEE ALSO
config(5) openssl-fipsinstall(1)

## HISTORY
This functionality was added in OpenSSL 3.0.

## COPYRIGHT
Copyright 2019-2025 The OpenSSL Project Authors. All Rights Reserved.

Licensed under the Apache License 2.0 (the "License"). You may not use this file except in compliance with the License. You can obtain a copy in the file LICENSE in the source distribution or at <https://www.openssl.org/source/license.html>.


title: x509v3_config(5ossl)

text:
# x509v3_config(5ossl)

## NAME
x509v3_config - X509 V3 certificate extension configuration format

## DESCRIPTION
Several OpenSSL commands can add extensions to a certificate or certificate request based on the contents of a configuration file and CLI options such as -addext. The syntax of configuration files is described in config(5). The commands typically have an option to specify the name of the configuration file, and a section within that file; see the documentation of the individual command for details.

This page uses extensions as the name of the section, when needed in examples.

Each entry in the extension section takes the form:

```
 name = [critical, ]value(s)
```

If critical is present then the extension will be marked as critical.

If multiple entries are processed for the same extension name, later entries override earlier ones with the same name.

The format of values depends on the value of name, many have a type-value pairing where the type and value are separated by a colon. There are four main types of extension:

```
 string
 multi-valued
 raw
 arbitrary
```

Each is described in the following paragraphs.

String extensions simply have a string which contains either the value itself or how it is obtained.

Multi-valued extensions have a short form and a long form. The short form is a comma-separated list of names and values:

```
 basicConstraints = critical, CA:true, pathlen:1
```

The long form allows the values to be placed in a separate section:

```
 [extensions]
 basicConstraints = critical, @basic_constraints
 [basic_constraints]
 CA = true
 pathlen = 1
```

Both forms are equivalent.

If an extension is multi-value and a field value must contain a comma the long form must be used otherwise the comma would be misinterpreted as a field separator. For example:

```
 subjectAltName = URI:ldap://somehost.com/CN=foo,OU=bar
```

will produce an error but the equivalent form:

```
 [extensions]
 subjectAltName = @subject_alt_section
 [subject_alt_section]
 subjectAltName = URI:ldap://somehost.com/CN=foo,OU=bar
```

is valid.

OpenSSL does not support multiple occurrences of the same field within a section. In this example:

```
 [extensions]
 subjectAltName = @alt_section
 [alt_section]
 email = steve@example.com
 email = steve@example.org
```

will only recognize the last value. To specify multiple values append a numeric identifier, as shown here:

```
 [extensions]
 subjectAltName = @alt_section
 [alt_section]
 email.1 = steve@example.com
 email.2 = steve@example.org
```

The syntax of raw extensions is defined by the source code that parses the extension but should be documented. See "Certificate Policies" for an example of a raw extension.

If an extension type is unsupported, then the arbitrary extension syntax must be used, see the "ARBITRARY EXTENSIONS" section for more details.

## STANDARD EXTENSIONS
The following sections describe the syntax of each supported extension. They do not define the semantics of the extension.

### Basic Constraints
This is a multi-valued extension which indicates whether a certificate is a CA certificate. The first value is CA followed by TRUE or FALSE. If CA is TRUE then an optional pathlen name followed by a nonnegative value can be included.

For example:

```
 basicConstraints = CA:TRUE
 basicConstraints = CA:FALSE
 basicConstraints = critical, CA:TRUE, pathlen:1
```

A CA certificate must include the basicConstraints name with the CA parameter set to TRUE. An end-user certificate must either have CA:FALSE or omit the extension entirely. The pathlen parameter specifies the maximum number of CAs that can appear below this one in a chain. A pathlen of zero means the CA cannot sign any sub-CA's, and can only sign end-entity certificates.

### Key Usage
Key usage is a multi-valued extension consisting of a list of names of the permitted key usages. The defined values are: "digitalSignature", "nonRepudiation", "keyEncipherment", "dataEncipherment", "keyAgreement", "keyCertSign", "cRLSign", "encipherOnly", and "decipherOnly".

Examples:

```
 keyUsage = digitalSignature, nonRepudiation
 keyUsage = critical, keyCertSign
```

### Extended Key Usage
This extension consists of a list of values indicating purposes for which the certificate public key can be used. Each value can be either a short text name or an OID. The following text names, and their intended meaning, are known:

```
 Value                  Meaning according to RFC 5280 etc.
 -----                  ----------------------------------
 serverAuth             SSL/TLS WWW Server Authentication
 clientAuth             SSL/TLS WWW Client Authentication
 codeSigning            Code Signing
 emailProtection        E-mail Protection (S/MIME)
 timeStamping           Trusted Timestamping
 OCSPSigning            OCSP Signing
 ipsecIKE               ipsec Internet Key Exchange
 msCodeInd              Microsoft Individual Code Signing (authenticode)
 msCodeCom              Microsoft Commercial Code Signing (authenticode)
 msCTLSign              Microsoft Trust List Signing
 msEFS                  Microsoft Encrypted File System
```

While IETF RFC 5280 says that id-kp-serverAuth and id-kp-clientAuth are only for WWW use, in practice they are used for all kinds of TLS clients and servers, and this is what OpenSSL assumes as well.

Examples:

```
 extendedKeyUsage = critical, codeSigning, 1.2.3.4
 extendedKeyUsage = serverAuth, clientAuth
```

### Subject Key Identifier
The SKID extension specification has a value with three choices.

none

No SKID extension will be included.

hash

The process specified in RFC 5280 section 4.2.1.2. (1) is followed: The keyIdentifier is composed of the 160-bit SHA-1 hash of the value of the BIT STRING subjectPublicKey (excluding the tag, length, and number of unused bits).

A hex string (possibly with ":" separating bytes)

The provided value is output directly. This choice is strongly discouraged.

By default the x509, req, and ca apps behave as if hash was given.

Example:

```
 subjectKeyIdentifier = hash
```

### Authority Key Identifier
The AKID extension specification may have the value none indicating that no AKID shall be included. Otherwise it may have the value keyid or issuer or both of them, separated by ",". Either or both can have the option always, indicated by putting a colon ":" between the value and this option. For self-signed certificates the AKID is suppressed unless always is present.

By default the x509, req, and ca apps behave as if none was given for self-signed certificates and keyid"," issuer otherwise.

If keyid is present, an attempt is made to copy the subject key identifier (SKID) from the issuer certificate except if the issuer certificate is the same as the current one and it is not self-signed. The hash of the public key related to the signing key is taken as fallback if the issuer certificate is the same as the current certificate. If always is present but no value can be obtained, an error is returned.

If issuer is present, and in addition it has the option always specified or keyid is not present, then the issuer DN and serial number are copied from the issuer certificate. If this fails, an error is returned.

Examples:

```
 authorityKeyIdentifier = keyid, issuer
 authorityKeyIdentifier = keyid, issuer:always
```

### Subject Alternative Name
This is a multi-valued extension that supports several types of name identifier, including email (an email address), URI (a uniform resource indicator), DNS (a DNS domain name), RID (a registered ID: OBJECT IDENTIFIER), IP (an IP address), dirName (a distinguished name), and otherName. The syntax of each is described in the following paragraphs.

The email option has two special values. "copy" will automatically include any email addresses contained in the certificate subject name in the extension. "move" will automatically move any email addresses from the certificate subject name to the extension.

The IP address used in the IP option can be in either IPv4 or IPv6 format.

The value of dirName is specifies the configuration section containing the distinguished name to use, as a set of name-value pairs. Multi-valued AVAs can be formed by prefacing the name with a + character.

The value of otherName can include arbitrary data associated with an OID; the value should be the OID followed by a semicolon and the content in specified using the syntax in ASN1_generate_nconf(3).

Examples:

```
 subjectAltName = email:copy, email:my@example.com, URI:http://my.example.com/
 subjectAltName = IP:192.168.7.1
 subjectAltName = IP:13::17
 subjectAltName = email:my@example.com, RID:1.2.3.4
 subjectAltName = otherName:1.2.3.4;UTF8:some other identifier
 [extensions]
 subjectAltName = dirName:dir_sect
 [dir_sect]
 C = UK
 O = My Organization
 OU = My Unit
 CN = My Name
```

Non-ASCII Email Address conforming the syntax defined in Section 3.3 of RFC 6531 are provided as otherName.SmtpUTF8Mailbox. According to RFC 8398, the email address should be provided as UTF8String. To enforce the valid representation in the certificate, the SmtpUTF8Mailbox should be provided as follows

```
 subjectAltName=@alts
 [alts]
 otherName = 1.3.6.1.5.5.7.8.9;FORMAT:UTF8,UTF8String:nonasciiname.example.com
```

### Issuer Alternative Name
This extension supports most of the options of subject alternative name; it does not support email:copy. It also adds issuer:copy as an allowed value, which copies any subject alternative names from the issuer certificate, if possible.

Example:

```
 issuerAltName = issuer:copy
```

### Authority Info Access
This extension gives details about how to retrieve information that related to the certificate that the CA makes available. The syntax is access_id;location, where access_id is an object identifier (although only a few values are well-known) and location has the same syntax as subject alternative name (except that email:copy is not supported).

Possible values for access_id include OCSP (OCSP responder), caIssuers (CA Issuers), ad_timestamping (AD Time Stamping), AD_DVCS (ad dvcs), caRepository (CA Repository).

Examples:

```
 authorityInfoAccess = OCSP;URI:http://ocsp.example.com/,caIssuers;URI:http://myca.example.com/ca.cer
 authorityInfoAccess = OCSP;URI:http://ocsp.example.com/
```

### CRL distribution points
This is a multi-valued extension whose values can be either a name-value pair using the same form as subject alternative name or a single value specifying the section name containing all the distribution point values.

When a name-value pair is used, a DistributionPoint extension will be set with the given value as the fullName field as the distributionPoint value, and the reasons and cRLIssuer fields will be omitted.

When a single option is used, the value specifies the section, and that section can have the following items:

fullname

The full name of the distribution point, in the same format as the subject alternative name.

relativename

The value is taken as a distinguished name fragment that is set as the value of the nameRelativeToCRLIssuer field.

CRLIssuer

The value must in the same format as the subject alternative name.

reasons

A multi-value field that contains the reasons for revocation. The recognized values are: "keyCompromise", "CACompromise", "affiliationChanged", "superseded", "cessationOfOperation", "certificateHold", "privilegeWithdrawn", and "AACompromise".

Only one of fullname or relativename should be specified.

Simple examples:

```
 crlDistributionPoints = URI:http://example.com/myca.crl
 crlDistributionPoints = URI:http://example.com/myca.crl, URI:http://example.org/my.crl
```

Full distribution point example:

```
 [extensions]
 crlDistributionPoints = crldp1_section
 [crldp1_section]
 fullname = URI:http://example.com/myca.crl
 CRLissuer = dirName:issuer_sect
 reasons = keyCompromise, CACompromise
 [issuer_sect]
 C = UK
 O = Organisation
 CN = Some Name
```

### Issuing Distribution Point
This extension should only appear in CRLs. It is a multi-valued extension whose syntax is similar to the "section" pointed to by the CRL distribution points extension. The following names have meaning:

fullname

The full name of the distribution point, in the same format as the subject alternative name.

relativename

The value is taken as a distinguished name fragment that is set as the value of the nameRelativeToCRLIssuer field.

onlysomereasons

A multi-value field that contains the reasons for revocation. The recognized values are: "keyCompromise", "CACompromise", "affiliationChanged", "superseded", "cessationOfOperation", "certificateHold", "privilegeWithdrawn", and "AACompromise".

onlyuser, onlyCA, onlyAA, indirectCRL

The value for each of these names is a boolean.

Example:

```
 [extensions]
 issuingDistributionPoint = critical, @idp_section
 [idp_section]
 fullname = URI:http://example.com/myca.crl
 indirectCRL = TRUE
 onlysomereasons = keyCompromise, CACompromise
```

### Certificate Policies
This is a raw extension that supports all of the defined fields of the certificate extension.

Policies without qualifiers are specified by giving the OID. Multiple policies are comma-separated. For example:

```
 certificatePolicies = 1.2.4.5, 1.1.3.4
```

To include policy qualifiers, use the "@section" syntax to point to a section that specifies all the information.

The section referred to must include the policy OID using the name policyIdentifier. cPSuri qualifiers can be included using the syntax:

```
 CPS.nnn = value
```

where "nnn" is a number.

userNotice qualifiers can be set using the syntax:

```
 userNotice.nnn = @notice
```

The value of the userNotice qualifier is specified in the relevant section. This section can include explicitText, organization, and noticeNumbers options. explicitText and organization are text strings, noticeNumbers is a comma separated list of numbers. The organization and noticeNumbers options (if included) must BOTH be present. Some software might require the ia5org option at the top level; this changes the encoding from Displaytext to IA5String.

Example:

```
 [extensions]
 certificatePolicies = ia5org, 1.2.3.4, 1.5.6.7.8, @polsect
 [polsect]
 policyIdentifier = 1.3.5.8
 CPS.1 = "http://my.host.example.com/"
 CPS.2 = "http://my.your.example.com/"
 userNotice.1 = @notice
 [notice]
 explicitText = "Explicit Text Here"
 organization = "Organisation Name"
 noticeNumbers = 1, 2, 3, 4
```

The character encoding of explicitText can be specified by prefixing the value with UTF8, BMP, or VISIBLE followed by colon. For example:

```
 [notice]
 explicitText = "UTF8:Explicit Text Here"
```

### Policy Constraints
This is a multi-valued extension which consisting of the names requireExplicitPolicy or inhibitPolicyMapping and a non negative integer value. At least one component must be present.

Example:

```
 policyConstraints = requireExplicitPolicy:3
```

### Inhibit Any Policy
This is a string extension whose value must be a non negative integer.

Example:

```
 inhibitAnyPolicy = 2
```

### Name Constraints
This is a multi-valued extension. The name should begin with the word permitted or excluded followed by a ;. The rest of the name and the value follows the syntax of subjectAltName except email:copy is not supported and the IP form should consist of an IP addresses and subnet mask separated by a /.

Examples:

```
 nameConstraints = permitted;IP:192.168.0.0/255.255.0.0
 nameConstraints = permitted;email:.example.com
 nameConstraints = excluded;email:.com
```

### OCSP No Check
This is a string extension. It is parsed, but ignored.

Example:

```
 noCheck = ignored
```

### TLS Feature (aka Must Staple)
This is a multi-valued extension consisting of a list of TLS extension identifiers. Each identifier may be a number (0..65535) or a supported name. When a TLS client sends a listed extension, the TLS server is expected to include that extension in its reply.

The supported names are: status_request and status_request_v2.

Example:

```
 tlsfeature = status_request
```

## DEPRECATED EXTENSIONS
The following extensions are non standard, Netscape specific and largely obsolete. Their use in new applications is discouraged.

### Netscape String extensions
Netscape Comment (nsComment) is a string extension containing a comment which will be displayed when the certificate is viewed in some browsers. Other extensions of this type are: nsBaseUrl, nsRevocationUrl, nsCaRevocationUrl, nsRenewalUrl, nsCaPolicyUrl and nsSslServerName.

### Netscape Certificate Type
This is a multi-valued extensions which consists of a list of flags to be included. It was used to indicate the purposes for which a certificate could be used. The basicConstraints, keyUsage and extended key usage extensions are now used instead.

Acceptable values for nsCertType are: client, server, email, objsign, reserved, sslCA, emailCA, objCA.

## ARBITRARY EXTENSIONS
If an extension is not supported by the OpenSSL code then it must be encoded using the arbitrary extension format. It is also possible to use the arbitrary format for supported extensions. Extreme care should be taken to ensure that the data is formatted correctly for the given extension type.

There are two ways to encode arbitrary extensions.

The first way is to use the word ASN1 followed by the extension content using the same syntax as ASN1_generate_nconf(3). For example:

```
 [extensions]
 1.2.3.4 = critical, ASN1:UTF8String:Some random data
 1.2.3.4.1 = ASN1:SEQUENCE:seq_sect
 [seq_sect]
 field1 = UTF8:field1
 field2 = UTF8:field2
```

It is also possible to use the word DER to include the raw encoded data in any extension.

```
 1.2.3.4 = critical, DER:01:02:03:04
 1.2.3.4.1 = DER:01020304
```

The value following DER is a hex dump of the DER encoding of the extension Any extension can be placed in this form to override the default behaviour. For example:

```
 basicConstraints = critical, DER:00:01:02:03
```

## WARNINGS
There is no guarantee that a specific implementation will process a given extension. It may therefore be sometimes possible to use certificates for purposes prohibited by their extensions because a specific application does not recognize or honour the values of the relevant extensions.

The DER and ASN1 options should be used with caution. It is possible to create invalid extensions if they are not used carefully.

## SEE ALSO
openssl-req(1), openssl-ca(1), openssl-x509(1), ASN1_generate_nconf(3)

## COPYRIGHT
Copyright 2004-2023 The OpenSSL Project Authors. All Rights Reserved.

Licensed under the Apache License 2.0 (the "License"). You may not use this file except in compliance with the License. You can obtain a copy in the file LICENSE in the source distribution or at <https://www.openssl.org/source/license.html>.