1.\" $OpenBSD: ssh-add.1,v 1.84 2022/02/04 02:49:17 dtucker 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: February 4 2022 $ 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 cDdKkLlqvXx 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.Nm ssh-add 56.Fl e Ar pkcs11 57.Nm ssh-add 58.Fl T 59.Ar pubkey ... 60.Sh DESCRIPTION 61.Nm 62adds private key identities to the authentication agent, 63.Xr ssh-agent 1 . 64When run without arguments, it adds the files 65.Pa ~/.ssh/id_rsa , 66.Pa ~/.ssh/id_ecdsa , 67.Pa ~/.ssh/id_ecdsa_sk , 68.Pa ~/.ssh/id_ed25519 , 69.Pa ~/.ssh/id_ed25519_sk , 70and 71.Pa ~/.ssh/id_dsa . 72After loading a private key, 73.Nm 74will try to load corresponding certificate information from the 75filename obtained by appending 76.Pa -cert.pub 77to the name of the private key file. 78Alternative file names can be given on the command line. 79.Pp 80If any file requires a passphrase, 81.Nm 82asks for the passphrase from the user. 83The passphrase is read from the user's tty. 84.Nm 85retries the last passphrase if multiple identity files are given. 86.Pp 87The authentication agent must be running and the 88.Ev SSH_AUTH_SOCK 89environment variable must contain the name of its socket for 90.Nm 91to work. 92.Pp 93The options are as follows: 94.Bl -tag -width Ds 95.It Fl c 96Indicates that added identities should be subject to confirmation before 97being used for authentication. 98Confirmation is performed by 99.Xr ssh-askpass 1 . 100Successful confirmation is signaled by a zero exit status from 101.Xr ssh-askpass 1 , 102rather than text entered into the requester. 103.It Fl D 104Deletes all identities from the agent. 105.It Fl d 106Instead of adding identities, removes identities from the agent. 107If 108.Nm 109has been run without arguments, the keys for the default identities and 110their corresponding certificates will be removed. 111Otherwise, the argument list will be interpreted as a list of paths to 112public key files to specify keys and certificates to be removed from the agent. 113If no public key is found at a given path, 114.Nm 115will append 116.Pa .pub 117and retry. 118If the argument list consists of 119.Dq - 120then 121.Nm 122will read public keys to be removed from standard input. 123.It Fl E Ar fingerprint_hash 124Specifies the hash algorithm used when displaying key fingerprints. 125Valid options are: 126.Dq md5 127and 128.Dq sha256 . 129The default is 130.Dq sha256 . 131.It Fl e Ar pkcs11 132Remove keys provided by the PKCS#11 shared library 133.Ar pkcs11 . 134.It Fl H Ar hostkey_file 135Specifies a known hosts file to look up hostkeys when using 136destination-constrained keys via the 137.Fl h 138flag. 139This option may be specified multiple times to allow multiple files to be 140searched. 141If no files are specified, 142.Nm 143will use the default 144.Xr ssh_config 5 145known hosts files: 146.Pa ~/.ssh/known_hosts , 147.Pa ~/.ssh/known_hosts2 , 148.Pa /etc/ssh/ssh_known_hosts , 149and 150.Pa /etc/ssh/ssh_known_hosts2 . 151.It Fl h Ar destination_constraint 152When adding keys, constrain them to be usable only through specific hosts or to 153specific destinations. 154.Pp 155Destination constraints of the form 156.Sq [user@]dest-hostname 157permit use of the key only from the origin host (the one running 158.Xr ssh-agent 1 ) 159to the listed destination host, with optional user name. 160.Pp 161Constraints of the form 162.Sq src-hostname>[user@]dst-hostname 163allow a key available on a forwarded 164.Xr ssh-agent 1 165to be used through a particular host (as specified by 166.Sq src-hostname ) 167to authenticate to a further host, 168specified by 169.Sq dst-hostname . 170.Pp 171Multiple destination constraints may be added when loading keys. 172When attempting authentication with a key that has destination constraints, 173the whole connection path, including 174.Xr ssh-agent 1 175forwarding, is tested against those constraints and each 176hop must be permitted for the attempt to succeed. 177For example, if key is forwarded to a remote host, 178.Sq host-b , 179and is attempting authentication to another host, 180.Sq host-c , 181then the operation will be successful only if 182.Sq host-b 183was permitted from the origin host and the subsequent 184.Sq host-b>host-c 185hop is also permitted by destination constraints. 186.Pp 187Hosts are identified by their host keys, and are looked up from known hosts 188files by 189.Nm . 190Wildcards patterns may be used for hostnames and certificate host 191keys are supported. 192By default, keys added by 193.Nm 194are not destination constrained. 195.Pp 196Destination constraints were added in OpenSSH release 8.9. 197Support in both the remote SSH client and server is required when using 198destination-constrained keys over a forwarded 199.Xr ssh-agent 1 200channel. 201.Pp 202It is also important to note that destination constraints can only be 203enforced by 204.Xr ssh-agent 1 205when a key is used, or when it is forwarded by a 206.Sy cooperating 207.Xr ssh 1 . 208Specifically, it does not prevent an attacker with access to a remote 209.Ev SSH_AUTH_SOCK 210from forwarding it again and using it on a different host (but only to 211a permitted destination). 212.It Fl K 213Load resident keys from a FIDO authenticator. 214.It Fl k 215When loading keys into or deleting keys from the agent, process plain private 216keys only and skip certificates. 217.It Fl L 218Lists public key parameters of all identities currently represented 219by the agent. 220.It Fl l 221Lists fingerprints of all identities currently represented by the agent. 222.It Fl q 223Be quiet after a successful operation. 224.It Fl S Ar provider 225Specifies a path to a library that will be used when adding 226FIDO authenticator-hosted keys, overriding the default of using the 227internal USB HID support. 228.It Fl s Ar pkcs11 229Add keys provided by the PKCS#11 shared library 230.Ar pkcs11 . 231.It Fl T Ar pubkey ... 232Tests whether the private keys that correspond to the specified 233.Ar pubkey 234files are usable by performing sign and verify operations on each. 235.It Fl t Ar life 236Set a maximum lifetime when adding identities to an agent. 237The lifetime may be specified in seconds or in a time format 238specified in 239.Xr sshd_config 5 . 240.It Fl v 241Verbose mode. 242Causes 243.Nm 244to print debugging messages about its progress. 245This is helpful in debugging problems. 246Multiple 247.Fl v 248options increase the verbosity. 249The maximum is 3. 250.It Fl X 251Unlock the agent. 252.It Fl x 253Lock the agent with a password. 254.El 255.Sh ENVIRONMENT 256.Bl -tag -width Ds 257.It Ev "DISPLAY", "SSH_ASKPASS" and "SSH_ASKPASS_REQUIRE" 258If 259.Nm 260needs a passphrase, it will read the passphrase from the current 261terminal if it was run from a terminal. 262If 263.Nm 264does not have a terminal associated with it but 265.Ev DISPLAY 266and 267.Ev SSH_ASKPASS 268are set, it will execute the program specified by 269.Ev SSH_ASKPASS 270(by default 271.Dq ssh-askpass ) 272and open an X11 window to read the passphrase. 273This is particularly useful when calling 274.Nm 275from a 276.Pa .xsession 277or related script. 278.Pp 279.Ev SSH_ASKPASS_REQUIRE 280allows further control over the use of an askpass program. 281If this variable is set to 282.Dq never 283then 284.Nm 285will never attempt to use one. 286If it is set to 287.Dq prefer , 288then 289.Nm 290will prefer to use the askpass program instead of the TTY when requesting 291passwords. 292Finally, if the variable is set to 293.Dq force , 294then the askpass program will be used for all passphrase input regardless 295of whether 296.Ev DISPLAY 297is set. 298.It Ev SSH_AUTH_SOCK 299Identifies the path of a 300.Ux Ns -domain 301socket used to communicate with the agent. 302.It Ev SSH_SK_PROVIDER 303Specifies a path to a library that will be used when loading any 304FIDO authenticator-hosted keys, overriding the default of using 305the built-in USB HID support. 306.El 307.Sh FILES 308.Bl -tag -width Ds -compact 309.It Pa ~/.ssh/id_dsa 310.It Pa ~/.ssh/id_ecdsa 311.It Pa ~/.ssh/id_ecdsa_sk 312.It Pa ~/.ssh/id_ed25519 313.It Pa ~/.ssh/id_ed25519_sk 314.It Pa ~/.ssh/id_rsa 315Contains the DSA, ECDSA, authenticator-hosted ECDSA, Ed25519, 316authenticator-hosted Ed25519 or RSA authentication identity of the user. 317.El 318.Pp 319Identity files should not be readable by anyone but the user. 320Note that 321.Nm 322ignores identity files if they are accessible by others. 323.Sh EXIT STATUS 324Exit status is 0 on success, 1 if the specified command fails, 325and 2 if 326.Nm 327is unable to contact the authentication agent. 328.Sh SEE ALSO 329.Xr ssh 1 , 330.Xr ssh-agent 1 , 331.Xr ssh-askpass 1 , 332.Xr ssh-keygen 1 , 333.Xr sshd 8 334.Sh AUTHORS 335OpenSSH is a derivative of the original and free 336ssh 1.2.12 release by Tatu Ylonen. 337Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, 338Theo de Raadt and Dug Song 339removed many bugs, re-added newer features and 340created OpenSSH. 341Markus Friedl contributed the support for SSH 342protocol versions 1.5 and 2.0. 343