.\" $OpenBSD: ssh-add.1,v 1.87 2024/06/17 08:30:29 djm Exp $ .\" .\" Author: Tatu Ylonen .\" Copyright (c) 1995 Tatu Ylonen , Espoo, Finland .\" All rights reserved .\" .\" As far as I am concerned, the code I have written for this software .\" can be used freely for any purpose. Any derived versions of this .\" software must be clearly marked as such, and if the derived work is .\" incompatible with the protocol description in the RFC file, it must be .\" called by a name other than "ssh" or "Secure Shell". .\" .\" .\" Copyright (c) 1999,2000 Markus Friedl. All rights reserved. .\" Copyright (c) 1999 Aaron Campbell. All rights reserved. .\" Copyright (c) 1999 Theo de Raadt. All rights reserved. .\" .\" Redistribution and use in source and binary forms, with or without .\" modification, are permitted provided that the following conditions .\" are met: .\" 1. Redistributions of source code must retain the above copyright .\" notice, this list of conditions and the following disclaimer. .\" 2. Redistributions in binary form must reproduce the above copyright .\" notice, this list of conditions and the following disclaimer in the .\" documentation and/or other materials provided with the distribution. .\" .\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR .\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES .\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. .\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, .\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT .\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, .\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY .\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT .\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF .\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. .\" .Dd $Mdocdate: June 17 2024 $ .Dt SSH-ADD 1 .Os .Sh NAME .Nm ssh-add .Nd adds private key identities to the OpenSSH authentication agent .Sh SYNOPSIS .Nm ssh-add .Op Fl CcDdKkLlqvXx .Op Fl E Ar fingerprint_hash .Op Fl H Ar hostkey_file .Op Fl h Ar destination_constraint .Op Fl S Ar provider .Op Fl t Ar life .Op Ar .Nm ssh-add .Fl s Ar pkcs11 .Op Fl Cv .Op Ar certificate ... .Nm ssh-add .Fl e Ar pkcs11 .Nm ssh-add .Fl T .Ar pubkey ... .Sh DESCRIPTION .Nm adds private key identities to the authentication agent, .Xr ssh-agent 1 . When run without arguments, it adds the files .Pa ~/.ssh/id_rsa , .Pa ~/.ssh/id_ecdsa , .Pa ~/.ssh/id_ecdsa_sk , .Pa ~/.ssh/id_ed25519 and .Pa ~/.ssh/id_ed25519_sk . After loading a private key, .Nm will try to load corresponding certificate information from the filename obtained by appending .Pa -cert.pub to the name of the private key file. Alternative file names can be given on the command line. .Pp If any file requires a passphrase, .Nm asks for the passphrase from the user. The passphrase is read from the user's tty. .Nm retries the last passphrase if multiple identity files are given. .Pp The authentication agent must be running and the .Ev SSH_AUTH_SOCK environment variable must contain the name of its socket for .Nm to work. .Pp The options are as follows: .Bl -tag -width Ds .It Fl C When loading keys into or deleting keys from the agent, process certificates only and skip plain keys. .It Fl c Indicates that added identities should be subject to confirmation before being used for authentication. Confirmation is performed by .Xr ssh-askpass 1 . Successful confirmation is signaled by a zero exit status from .Xr ssh-askpass 1 , rather than text entered into the requester. .It Fl D Deletes all identities from the agent. .It Fl d Instead of adding identities, removes identities from the agent. If .Nm has been run without arguments, the keys for the default identities and their corresponding certificates will be removed. Otherwise, the argument list will be interpreted as a list of paths to public key files to specify keys and certificates to be removed from the agent. If no public key is found at a given path, .Nm will append .Pa .pub and retry. If the argument list consists of .Dq - then .Nm will read public keys to be removed from standard input. .It Fl E Ar fingerprint_hash Specifies the hash algorithm used when displaying key fingerprints. Valid options are: .Dq md5 and .Dq sha256 . The default is .Dq sha256 . .It Fl e Ar pkcs11 Remove keys provided by the PKCS#11 shared library .Ar pkcs11 . .It Fl H Ar hostkey_file Specifies a known hosts file to look up hostkeys when using destination-constrained keys via the .Fl h flag. This option may be specified multiple times to allow multiple files to be searched. If no files are specified, .Nm will use the default .Xr ssh_config 5 known hosts files: .Pa ~/.ssh/known_hosts , .Pa ~/.ssh/known_hosts2 , .Pa /etc/ssh_known_hosts , and .Pa /etc/ssh_known_hosts2 . .It Fl h Ar destination_constraint When adding keys, constrain them to be usable only through specific hosts or to specific destinations. .Pp Destination constraints of the form .Sq [user@]dest-hostname permit use of the key only from the origin host (the one running .Xr ssh-agent 1 ) to the listed destination host, with optional user name. .Pp Constraints of the form .Sq src-hostname>[user@]dst-hostname allow a key available on a forwarded .Xr ssh-agent 1 to be used through a particular host (as specified by .Sq src-hostname ) to authenticate to a further host, specified by .Sq dst-hostname . .Pp Multiple destination constraints may be added when loading keys. When attempting authentication with a key that has destination constraints, the whole connection path, including .Xr ssh-agent 1 forwarding, is tested against those constraints and each hop must be permitted for the attempt to succeed. For example, if key is forwarded to a remote host, .Sq host-b , and is attempting authentication to another host, .Sq host-c , then the operation will be successful only if .Sq host-b was permitted from the origin host and the subsequent .Sq host-b>host-c hop is also permitted by destination constraints. .Pp Hosts are identified by their host keys, and are looked up from known hosts files by .Nm . Wildcards patterns may be used for hostnames and certificate host keys are supported. By default, keys added by .Nm are not destination constrained. .Pp Destination constraints were added in OpenSSH release 8.9. Support in both the remote SSH client and server is required when using destination-constrained keys over a forwarded .Xr ssh-agent 1 channel. .Pp It is also important to note that destination constraints can only be enforced by .Xr ssh-agent 1 when a key is used, or when it is forwarded by a .Sy cooperating .Xr ssh 1 . Specifically, it does not prevent an attacker with access to a remote .Ev SSH_AUTH_SOCK from forwarding it again and using it on a different host (but only to a permitted destination). .It Fl K Load resident keys from a FIDO authenticator. .It Fl k When loading keys into or deleting keys from the agent, process plain private keys only and skip certificates. .It Fl L Lists public key parameters of all identities currently represented by the agent. .It Fl l Lists fingerprints of all identities currently represented by the agent. .It Fl q Be quiet after a successful operation. .It Fl S Ar provider Specifies a path to a library that will be used when adding FIDO authenticator-hosted keys, overriding the default of using the internal USB HID support. .It Fl s Ar pkcs11 Add keys provided by the PKCS#11 shared library .Ar pkcs11 . Certificate files may optionally be listed as command-line arguments. If these are present, then they will be loaded into the agent using any corresponding private keys loaded from the PKCS#11 token. .It Fl T Ar pubkey ... Tests whether the private keys that correspond to the specified .Ar pubkey files are usable by performing sign and verify operations on each. .It Fl t Ar life Set a maximum lifetime when adding identities to an agent. The lifetime may be specified in seconds or in a time format specified in .Xr sshd_config 5 . .It Fl v Verbose mode. Causes .Nm to print debugging messages about its progress. This is helpful in debugging problems. Multiple .Fl v options increase the verbosity. The maximum is 3. .It Fl X Unlock the agent. .It Fl x Lock the agent with a password. .El .Sh ENVIRONMENT .Bl -tag -width Ds .It Ev "DISPLAY", "SSH_ASKPASS" and "SSH_ASKPASS_REQUIRE" If .Nm needs a passphrase, it will read the passphrase from the current terminal if it was run from a terminal. If .Nm does not have a terminal associated with it but .Ev DISPLAY and .Ev SSH_ASKPASS are set, it will execute the program specified by .Ev SSH_ASKPASS (by default .Dq ssh-askpass ) and open an X11 window to read the passphrase. This is particularly useful when calling .Nm from a .Pa .xsession or related script. .Pp .Ev SSH_ASKPASS_REQUIRE allows further control over the use of an askpass program. If this variable is set to .Dq never then .Nm will never attempt to use one. If it is set to .Dq prefer , then .Nm will prefer to use the askpass program instead of the TTY when requesting passwords. Finally, if the variable is set to .Dq force , then the askpass program will be used for all passphrase input regardless of whether .Ev DISPLAY is set. .It Ev SSH_AUTH_SOCK Identifies the path of a .Ux Ns -domain socket used to communicate with the agent. .It Ev SSH_SK_PROVIDER Specifies a path to a library that will be used when loading any FIDO authenticator-hosted keys, overriding the default of using the built-in USB HID support. .El .Sh FILES .Bl -tag -width Ds -compact .It Pa ~/.ssh/id_ecdsa .It Pa ~/.ssh/id_ecdsa_sk .It Pa ~/.ssh/id_ed25519 .It Pa ~/.ssh/id_ed25519_sk .It Pa ~/.ssh/id_rsa Contains the ECDSA, authenticator-hosted ECDSA, Ed25519, authenticator-hosted Ed25519 or RSA authentication identity of the user. .El .Pp Identity files should not be readable by anyone but the user. Note that .Nm ignores identity files if they are accessible by others. .Sh EXIT STATUS Exit status is 0 on success, 1 if the specified command fails, and 2 if .Nm is unable to contact the authentication agent. .Sh SEE ALSO .Xr ssh 1 , .Xr ssh-agent 1 , .Xr ssh-askpass 1 , .Xr ssh-keygen 1 , .Xr sshd 8 .Sh 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.