1.\" $OpenBSD: ssh-add.1,v 1.86 2023/12/19 06:57:34 jmc Exp $ 2.\" 3.\" Author: Tatu Ylonen <ylo@cs.hut.fi> 4.\" Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland 5.\" All rights reserved 6.\" 7.\" As far as I am concerned, the code I have written for this software 8.\" can be used freely for any purpose. Any derived versions of this 9.\" software must be clearly marked as such, and if the derived work is 10.\" incompatible with the protocol description in the RFC file, it must be 11.\" called by a name other than "ssh" or "Secure Shell". 12.\" 13.\" 14.\" Copyright (c) 1999,2000 Markus Friedl. All rights reserved. 15.\" Copyright (c) 1999 Aaron Campbell. All rights reserved. 16.\" Copyright (c) 1999 Theo de Raadt. All rights reserved. 17.\" 18.\" Redistribution and use in source and binary forms, with or without 19.\" modification, are permitted provided that the following conditions 20.\" are met: 21.\" 1. Redistributions of source code must retain the above copyright 22.\" notice, this list of conditions and the following disclaimer. 23.\" 2. Redistributions in binary form must reproduce the above copyright 24.\" notice, this list of conditions and the following disclaimer in the 25.\" documentation and/or other materials provided with the distribution. 26.\" 27.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR 28.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES 29.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. 30.\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, 31.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT 32.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 33.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 34.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 35.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF 36.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 37.\" 38.Dd $Mdocdate: December 19 2023 $ 39.Dt SSH-ADD 1 40.Os 41.Sh NAME 42.Nm ssh-add 43.Nd adds private key identities to the OpenSSH authentication agent 44.Sh SYNOPSIS 45.Nm ssh-add 46.Op Fl CcDdKkLlqvXx 47.Op Fl E Ar fingerprint_hash 48.Op Fl H Ar hostkey_file 49.Op Fl h Ar destination_constraint 50.Op Fl S Ar provider 51.Op Fl t Ar life 52.Op Ar 53.Nm ssh-add 54.Fl s Ar pkcs11 55.Op Fl Cv 56.Op Ar certificate ... 57.Nm ssh-add 58.Fl e Ar pkcs11 59.Nm ssh-add 60.Fl T 61.Ar pubkey ... 62.Sh DESCRIPTION 63.Nm 64adds private key identities to the authentication agent, 65.Xr ssh-agent 1 . 66When run without arguments, it adds the files 67.Pa ~/.ssh/id_rsa , 68.Pa ~/.ssh/id_ecdsa , 69.Pa ~/.ssh/id_ecdsa_sk , 70.Pa ~/.ssh/id_ed25519 , 71.Pa ~/.ssh/id_ed25519_sk , 72and 73.Pa ~/.ssh/id_dsa . 74After loading a private key, 75.Nm 76will try to load corresponding certificate information from the 77filename obtained by appending 78.Pa -cert.pub 79to the name of the private key file. 80Alternative file names can be given on the command line. 81.Pp 82If any file requires a passphrase, 83.Nm 84asks for the passphrase from the user. 85The passphrase is read from the user's tty. 86.Nm 87retries the last passphrase if multiple identity files are given. 88.Pp 89The authentication agent must be running and the 90.Ev SSH_AUTH_SOCK 91environment variable must contain the name of its socket for 92.Nm 93to work. 94.Pp 95The options are as follows: 96.Bl -tag -width Ds 97.It Fl C 98When loading keys into or deleting keys from the agent, process 99certificates only and skip plain keys. 100.It Fl c 101Indicates that added identities should be subject to confirmation before 102being used for authentication. 103Confirmation is performed by 104.Xr ssh-askpass 1 . 105Successful confirmation is signaled by a zero exit status from 106.Xr ssh-askpass 1 , 107rather than text entered into the requester. 108.It Fl D 109Deletes all identities from the agent. 110.It Fl d 111Instead of adding identities, removes identities from the agent. 112If 113.Nm 114has been run without arguments, the keys for the default identities and 115their corresponding certificates will be removed. 116Otherwise, the argument list will be interpreted as a list of paths to 117public key files to specify keys and certificates to be removed from the agent. 118If no public key is found at a given path, 119.Nm 120will append 121.Pa .pub 122and retry. 123If the argument list consists of 124.Dq - 125then 126.Nm 127will read public keys to be removed from standard input. 128.It Fl E Ar fingerprint_hash 129Specifies the hash algorithm used when displaying key fingerprints. 130Valid options are: 131.Dq md5 132and 133.Dq sha256 . 134The default is 135.Dq sha256 . 136.It Fl e Ar pkcs11 137Remove keys provided by the PKCS#11 shared library 138.Ar pkcs11 . 139.It Fl H Ar hostkey_file 140Specifies a known hosts file to look up hostkeys when using 141destination-constrained keys via the 142.Fl h 143flag. 144This option may be specified multiple times to allow multiple files to be 145searched. 146If no files are specified, 147.Nm 148will use the default 149.Xr ssh_config 5 150known hosts files: 151.Pa ~/.ssh/known_hosts , 152.Pa ~/.ssh/known_hosts2 , 153.Pa /etc/ssh/ssh_known_hosts , 154and 155.Pa /etc/ssh/ssh_known_hosts2 . 156.It Fl h Ar destination_constraint 157When adding keys, constrain them to be usable only through specific hosts or to 158specific destinations. 159.Pp 160Destination constraints of the form 161.Sq [user@]dest-hostname 162permit use of the key only from the origin host (the one running 163.Xr ssh-agent 1 ) 164to the listed destination host, with optional user name. 165.Pp 166Constraints of the form 167.Sq src-hostname>[user@]dst-hostname 168allow a key available on a forwarded 169.Xr ssh-agent 1 170to be used through a particular host (as specified by 171.Sq src-hostname ) 172to authenticate to a further host, 173specified by 174.Sq dst-hostname . 175.Pp 176Multiple destination constraints may be added when loading keys. 177When attempting authentication with a key that has destination constraints, 178the whole connection path, including 179.Xr ssh-agent 1 180forwarding, is tested against those constraints and each 181hop must be permitted for the attempt to succeed. 182For example, if key is forwarded to a remote host, 183.Sq host-b , 184and is attempting authentication to another host, 185.Sq host-c , 186then the operation will be successful only if 187.Sq host-b 188was permitted from the origin host and the subsequent 189.Sq host-b>host-c 190hop is also permitted by destination constraints. 191.Pp 192Hosts are identified by their host keys, and are looked up from known hosts 193files by 194.Nm . 195Wildcards patterns may be used for hostnames and certificate host 196keys are supported. 197By default, keys added by 198.Nm 199are not destination constrained. 200.Pp 201Destination constraints were added in OpenSSH release 8.9. 202Support in both the remote SSH client and server is required when using 203destination-constrained keys over a forwarded 204.Xr ssh-agent 1 205channel. 206.Pp 207It is also important to note that destination constraints can only be 208enforced by 209.Xr ssh-agent 1 210when a key is used, or when it is forwarded by a 211.Sy cooperating 212.Xr ssh 1 . 213Specifically, it does not prevent an attacker with access to a remote 214.Ev SSH_AUTH_SOCK 215from forwarding it again and using it on a different host (but only to 216a permitted destination). 217.It Fl K 218Load resident keys from a FIDO authenticator. 219.It Fl k 220When loading keys into or deleting keys from the agent, process plain private 221keys only and skip certificates. 222.It Fl L 223Lists public key parameters of all identities currently represented 224by the agent. 225.It Fl l 226Lists fingerprints of all identities currently represented by the agent. 227.It Fl q 228Be quiet after a successful operation. 229.It Fl S Ar provider 230Specifies a path to a library that will be used when adding 231FIDO authenticator-hosted keys, overriding the default of using the 232internal USB HID support. 233.It Fl s Ar pkcs11 234Add keys provided by the PKCS#11 shared library 235.Ar pkcs11 . 236Certificate files may optionally be listed as command-line arguments. 237If these are present, then they will be loaded into the agent using any 238corresponding private keys loaded from the PKCS#11 token. 239.It Fl T Ar pubkey ... 240Tests whether the private keys that correspond to the specified 241.Ar pubkey 242files are usable by performing sign and verify operations on each. 243.It Fl t Ar life 244Set a maximum lifetime when adding identities to an agent. 245The lifetime may be specified in seconds or in a time format 246specified in 247.Xr sshd_config 5 . 248.It Fl v 249Verbose mode. 250Causes 251.Nm 252to print debugging messages about its progress. 253This is helpful in debugging problems. 254Multiple 255.Fl v 256options increase the verbosity. 257The maximum is 3. 258.It Fl X 259Unlock the agent. 260.It Fl x 261Lock the agent with a password. 262.El 263.Sh ENVIRONMENT 264.Bl -tag -width Ds 265.It Ev "DISPLAY", "SSH_ASKPASS" and "SSH_ASKPASS_REQUIRE" 266If 267.Nm 268needs a passphrase, it will read the passphrase from the current 269terminal if it was run from a terminal. 270If 271.Nm 272does not have a terminal associated with it but 273.Ev DISPLAY 274and 275.Ev SSH_ASKPASS 276are set, it will execute the program specified by 277.Ev SSH_ASKPASS 278(by default 279.Dq ssh-askpass ) 280and open an X11 window to read the passphrase. 281This is particularly useful when calling 282.Nm 283from a 284.Pa .xsession 285or related script. 286.Pp 287.Ev SSH_ASKPASS_REQUIRE 288allows further control over the use of an askpass program. 289If this variable is set to 290.Dq never 291then 292.Nm 293will never attempt to use one. 294If it is set to 295.Dq prefer , 296then 297.Nm 298will prefer to use the askpass program instead of the TTY when requesting 299passwords. 300Finally, if the variable is set to 301.Dq force , 302then the askpass program will be used for all passphrase input regardless 303of whether 304.Ev DISPLAY 305is set. 306.It Ev SSH_AUTH_SOCK 307Identifies the path of a 308.Ux Ns -domain 309socket used to communicate with the agent. 310.It Ev SSH_SK_PROVIDER 311Specifies a path to a library that will be used when loading any 312FIDO authenticator-hosted keys, overriding the default of using 313the built-in USB HID support. 314.El 315.Sh FILES 316.Bl -tag -width Ds -compact 317.It Pa ~/.ssh/id_dsa 318.It Pa ~/.ssh/id_ecdsa 319.It Pa ~/.ssh/id_ecdsa_sk 320.It Pa ~/.ssh/id_ed25519 321.It Pa ~/.ssh/id_ed25519_sk 322.It Pa ~/.ssh/id_rsa 323Contains the DSA, ECDSA, authenticator-hosted ECDSA, Ed25519, 324authenticator-hosted Ed25519 or RSA authentication identity of the user. 325.El 326.Pp 327Identity files should not be readable by anyone but the user. 328Note that 329.Nm 330ignores identity files if they are accessible by others. 331.Sh EXIT STATUS 332Exit status is 0 on success, 1 if the specified command fails, 333and 2 if 334.Nm 335is unable to contact the authentication agent. 336.Sh SEE ALSO 337.Xr ssh 1 , 338.Xr ssh-agent 1 , 339.Xr ssh-askpass 1 , 340.Xr ssh-keygen 1 , 341.Xr sshd 8 342.Sh AUTHORS 343OpenSSH is a derivative of the original and free 344ssh 1.2.12 release by Tatu Ylonen. 345Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, 346Theo de Raadt and Dug Song 347removed many bugs, re-added newer features and 348created OpenSSH. 349Markus Friedl contributed the support for SSH 350protocol versions 1.5 and 2.0. 351