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diff --git a/ssh-keygen.0 b/ssh-keygen.0 new file mode 100644 index 0000000..95e4aa3 --- /dev/null +++ b/ssh-keygen.0 @@ -0,0 +1,910 @@ +SSH-KEYGEN(1) General Commands Manual SSH-KEYGEN(1) + +NAME + ssh-keygen M-bM-^@M-^S OpenSSH authentication key utility + +SYNOPSIS + ssh-keygen [-q] [-a rounds] [-b bits] [-C comment] [-f output_keyfile] + [-m format] [-N new_passphrase] [-O option] + [-t dsa | ecdsa | ecdsa-sk | ed25519 | ed25519-sk | rsa] + [-w provider] [-Z cipher] + ssh-keygen -p [-a rounds] [-f keyfile] [-m format] [-N new_passphrase] + [-P old_passphrase] [-Z cipher] + ssh-keygen -i [-f input_keyfile] [-m key_format] + ssh-keygen -e [-f input_keyfile] [-m key_format] + ssh-keygen -y [-f input_keyfile] + ssh-keygen -c [-a rounds] [-C comment] [-f keyfile] [-P passphrase] + ssh-keygen -l [-v] [-E fingerprint_hash] [-f input_keyfile] + ssh-keygen -B [-f input_keyfile] + ssh-keygen -D pkcs11 + ssh-keygen -F hostname [-lv] [-f known_hosts_file] + ssh-keygen -H [-f known_hosts_file] + ssh-keygen -K [-a rounds] [-w provider] + ssh-keygen -R hostname [-f known_hosts_file] + ssh-keygen -r hostname [-g] [-f input_keyfile] + ssh-keygen -M generate [-O option] output_file + ssh-keygen -M screen [-f input_file] [-O option] output_file + ssh-keygen -I certificate_identity -s ca_key [-hU] [-D pkcs11_provider] + [-n principals] [-O option] [-V validity_interval] + [-z serial_number] file ... + ssh-keygen -L [-f input_keyfile] + ssh-keygen -A [-a rounds] [-f prefix_path] + ssh-keygen -k -f krl_file [-u] [-s ca_public] [-z version_number] + file ... + ssh-keygen -Q [-l] -f krl_file file ... + ssh-keygen -Y find-principals [-O option] -s signature_file + -f allowed_signers_file + ssh-keygen -Y match-principals -I signer_identity -f allowed_signers_file + ssh-keygen -Y check-novalidate [-O option] -n namespace -s signature_file + ssh-keygen -Y sign [-O option] -f key_file -n namespace file ... + ssh-keygen -Y verify [-O option] -f allowed_signers_file + -I signer_identity -n namespace -s signature_file + [-r revocation_file] + +DESCRIPTION + ssh-keygen generates, manages and converts authentication keys for + ssh(1). ssh-keygen can create keys for use by SSH protocol version 2. + + The type of key to be generated is specified with the -t option. If + invoked without any arguments, ssh-keygen will generate an Ed25519 key. + + ssh-keygen is also used to generate groups for use in Diffie-Hellman + group exchange (DH-GEX). See the MODULI GENERATION section for details. + + Finally, ssh-keygen can be used to generate and update Key Revocation + Lists, and to test whether given keys have been revoked by one. See the + KEY REVOCATION LISTS section for details. + + Normally each user wishing to use SSH with public key authentication runs + this once to create the authentication key in ~/.ssh/id_dsa, + ~/.ssh/id_ecdsa, ~/.ssh/id_ecdsa_sk, ~/.ssh/id_ed25519, + ~/.ssh/id_ed25519_sk or ~/.ssh/id_rsa. Additionally, the system + administrator may use this to generate host keys, as seen in /etc/rc. + + Normally this program generates the key and asks for a file in which to + store the private key. The public key is stored in a file with the same + name but M-bM-^@M-^\.pubM-bM-^@M-^] appended. The program also asks for a passphrase. The + passphrase may be empty to indicate no passphrase (host keys must have an + empty passphrase), or it may be a string of arbitrary length. A + passphrase is similar to a password, except it can be a phrase with a + series of words, punctuation, numbers, whitespace, or any string of + characters you want. Good passphrases are 10-30 characters long, are not + simple sentences or otherwise easily guessable (English prose has only + 1-2 bits of entropy per character, and provides very bad passphrases), + and contain a mix of upper and lowercase letters, numbers, and non- + alphanumeric characters. The passphrase can be changed later by using + the -p option. + + There is no way to recover a lost passphrase. If the passphrase is lost + or forgotten, a new key must be generated and the corresponding public + key copied to other machines. + + ssh-keygen will by default write keys in an OpenSSH-specific format. + This format is preferred as it offers better protection for keys at rest + as well as allowing storage of key comments within the private key file + itself. The key comment may be useful to help identify the key. The + comment is initialized to M-bM-^@M-^\user@hostM-bM-^@M-^] when the key is created, but can be + changed using the -c option. + + It is still possible for ssh-keygen to write the previously-used PEM + format private keys using the -m flag. This may be used when generating + new keys, and existing new-format keys may be converted using this option + in conjunction with the -p (change passphrase) flag. + + After a key is generated, ssh-keygen will ask where the keys should be + placed to be activated. + + The options are as follows: + + -A Generate host keys of all default key types (rsa, ecdsa, and + ed25519) if they do not already exist. The host keys are + generated with the default key file path, an empty passphrase, + default bits for the key type, and default comment. If -f has + also been specified, its argument is used as a prefix to the + default path for the resulting host key files. This is used by + /etc/rc to generate new host keys. + + -a rounds + When saving a private key, this option specifies the number of + KDF (key derivation function, currently bcrypt_pbkdf(3)) rounds + used. Higher numbers result in slower passphrase verification + and increased resistance to brute-force password cracking (should + the keys be stolen). The default is 16 rounds. + + -B Show the bubblebabble digest of specified private or public key + file. + + -b bits + Specifies the number of bits in the key to create. For RSA keys, + the minimum size is 1024 bits and the default is 3072 bits. + Generally, 3072 bits is considered sufficient. DSA keys must be + exactly 1024 bits as specified by FIPS 186-2. For ECDSA keys, + the -b flag determines the key length by selecting from one of + three elliptic curve sizes: 256, 384 or 521 bits. Attempting to + use bit lengths other than these three values for ECDSA keys will + fail. ECDSA-SK, Ed25519 and Ed25519-SK keys have a fixed length + and the -b flag will be ignored. + + -C comment + Provides a new comment. + + -c Requests changing the comment in the private and public key + files. The program will prompt for the file containing the + private keys, for the passphrase if the key has one, and for the + new comment. + + -D pkcs11 + Download the public keys provided by the PKCS#11 shared library + pkcs11. When used in combination with -s, this option indicates + that a CA key resides in a PKCS#11 token (see the CERTIFICATES + section for details). + + -E fingerprint_hash + Specifies the hash algorithm used when displaying key + fingerprints. Valid options are: M-bM-^@M-^\md5M-bM-^@M-^] and M-bM-^@M-^\sha256M-bM-^@M-^]. The + default is M-bM-^@M-^\sha256M-bM-^@M-^]. + + -e This option will read a private or public OpenSSH key file and + print to stdout a public key in one of the formats specified by + the -m option. The default export format is M-bM-^@M-^\RFC4716M-bM-^@M-^]. This + option allows exporting OpenSSH keys for use by other programs, + including several commercial SSH implementations. + + -F hostname | [hostname]:port + Search for the specified hostname (with optional port number) in + a known_hosts file, listing any occurrences found. This option + is useful to find hashed host names or addresses and may also be + used in conjunction with the -H option to print found keys in a + hashed format. + + -f filename + Specifies the filename of the key file. + + -g Use generic DNS format when printing fingerprint resource records + using the -r command. + + -H Hash a known_hosts file. This replaces all hostnames and + addresses with hashed representations within the specified file; + the original content is moved to a file with a .old suffix. + These hashes may be used normally by ssh and sshd, but they do + not reveal identifying information should the file's contents be + disclosed. This option will not modify existing hashed hostnames + and is therefore safe to use on files that mix hashed and non- + hashed names. + + -h When signing a key, create a host certificate instead of a user + certificate. See the CERTIFICATES section for details. + + -I certificate_identity + Specify the key identity when signing a public key. See the + CERTIFICATES section for details. + + -i This option will read an unencrypted private (or public) key file + in the format specified by the -m option and print an OpenSSH + compatible private (or public) key to stdout. This option allows + importing keys from other software, including several commercial + SSH implementations. The default import format is M-bM-^@M-^\RFC4716M-bM-^@M-^]. + + -K Download resident keys from a FIDO authenticator. Public and + private key files will be written to the current directory for + each downloaded key. If multiple FIDO authenticators are + attached, keys will be downloaded from the first touched + authenticator. See the FIDO AUTHENTICATOR section for more + information. + + -k Generate a KRL file. In this mode, ssh-keygen will generate a + KRL file at the location specified via the -f flag that revokes + every key or certificate presented on the command line. + Keys/certificates to be revoked may be specified by public key + file or using the format described in the KEY REVOCATION LISTS + section. + + -L Prints the contents of one or more certificates. + + -l Show fingerprint of specified public key file. For RSA and DSA + keys ssh-keygen tries to find the matching public key file and + prints its fingerprint. If combined with -v, a visual ASCII art + representation of the key is supplied with the fingerprint. + + -M generate + Generate candidate Diffie-Hellman Group Exchange (DH-GEX) + parameters for eventual use by the + M-bM-^@M-^Xdiffie-hellman-group-exchange-*M-bM-^@M-^Y key exchange methods. The + numbers generated by this operation must be further screened + before use. See the MODULI GENERATION section for more + information. + + -M screen + Screen candidate parameters for Diffie-Hellman Group Exchange. + This will accept a list of candidate numbers and test that they + are safe (Sophie Germain) primes with acceptable group + generators. The results of this operation may be added to the + /etc/moduli file. See the MODULI GENERATION section for more + information. + + -m key_format + Specify a key format for key generation, the -i (import), -e + (export) conversion options, and the -p change passphrase + operation. The latter may be used to convert between OpenSSH + private key and PEM private key formats. The supported key + formats are: M-bM-^@M-^\RFC4716M-bM-^@M-^] (RFC 4716/SSH2 public or private key), + M-bM-^@M-^\PKCS8M-bM-^@M-^] (PKCS8 public or private key) or M-bM-^@M-^\PEMM-bM-^@M-^] (PEM public key). + By default OpenSSH will write newly-generated private keys in its + own format, but when converting public keys for export the + default format is M-bM-^@M-^\RFC4716M-bM-^@M-^]. Setting a format of M-bM-^@M-^\PEMM-bM-^@M-^] when + generating or updating a supported private key type will cause + the key to be stored in the legacy PEM private key format. + + -N new_passphrase + Provides the new passphrase. + + -n principals + Specify one or more principals (user or host names) to be + included in a certificate when signing a key. Multiple + principals may be specified, separated by commas. See the + CERTIFICATES section for details. + + -O option + Specify a key/value option. These are specific to the operation + that ssh-keygen has been requested to perform. + + When signing certificates, one of the options listed in the + CERTIFICATES section may be specified here. + + When performing moduli generation or screening, one of the + options listed in the MODULI GENERATION section may be specified. + + When generating FIDO authenticator-backed keys, the options + listed in the FIDO AUTHENTICATOR section may be specified. + + When performing signature-related options using the -Y flag, the + following options are accepted: + + hashalg=algorithm + Selects the hash algorithm to use for hashing the message + to be signed. Valid algorithms are M-bM-^@M-^\sha256M-bM-^@M-^] and + M-bM-^@M-^\sha512.M-bM-^@M-^] The default is M-bM-^@M-^\sha512.M-bM-^@M-^] + + print-pubkey + Print the full public key to standard output after + signature verification. + + verify-time=timestamp + Specifies a time to use when validating signatures + instead of the current time. The time may be specified + as a date or time in the YYYYMMDD[Z] or in + YYYYMMDDHHMM[SS][Z] formats. Dates and times will be + interpreted in the current system time zone unless + suffixed with a Z character, which causes them to be + interpreted in the UTC time zone. + + When generating SSHFP DNS records from public keys using the -r + flag, the following options are accepted: + + hashalg=algorithm + Selects a hash algorithm to use when printing SSHFP + records using the -D flag. Valid algorithms are M-bM-^@M-^\sha1M-bM-^@M-^] + and M-bM-^@M-^\sha256M-bM-^@M-^]. The default is to print both. + + The -O option may be specified multiple times. + + -P passphrase + Provides the (old) passphrase. + + -p Requests changing the passphrase of a private key file instead of + creating a new private key. The program will prompt for the file + containing the private key, for the old passphrase, and twice for + the new passphrase. + + -Q Test whether keys have been revoked in a KRL. If the -l option + is also specified then the contents of the KRL will be printed. + + -q Silence ssh-keygen. + + -R hostname | [hostname]:port + Removes all keys belonging to the specified hostname (with + optional port number) from a known_hosts file. This option is + useful to delete hashed hosts (see the -H option above). + + -r hostname + Print the SSHFP fingerprint resource record named hostname for + the specified public key file. + + -s ca_key + Certify (sign) a public key using the specified CA key. See the + CERTIFICATES section for details. + + When generating a KRL, -s specifies a path to a CA public key + file used to revoke certificates directly by key ID or serial + number. See the KEY REVOCATION LISTS section for details. + + -t dsa | ecdsa | ecdsa-sk | ed25519 | ed25519-sk | rsa + Specifies the type of key to create. The possible values are + M-bM-^@M-^\dsaM-bM-^@M-^], M-bM-^@M-^\ecdsaM-bM-^@M-^], M-bM-^@M-^\ecdsa-skM-bM-^@M-^], M-bM-^@M-^\ed25519M-bM-^@M-^], M-bM-^@M-^\ed25519-skM-bM-^@M-^], or M-bM-^@M-^\rsaM-bM-^@M-^]. + + This flag may also be used to specify the desired signature type + when signing certificates using an RSA CA key. The available RSA + signature variants are M-bM-^@M-^\ssh-rsaM-bM-^@M-^] (SHA1 signatures, not + recommended), M-bM-^@M-^\rsa-sha2-256M-bM-^@M-^], and M-bM-^@M-^\rsa-sha2-512M-bM-^@M-^] (the default). + + -U When used in combination with -s or -Y sign, this option + indicates that a CA key resides in a ssh-agent(1). See the + CERTIFICATES section for more information. + + -u Update a KRL. When specified with -k, keys listed via the + command line are added to the existing KRL rather than a new KRL + being created. + + -V validity_interval + Specify a validity interval when signing a certificate. A + validity interval may consist of a single time, indicating that + the certificate is valid beginning now and expiring at that time, + or may consist of two times separated by a colon to indicate an + explicit time interval. + + The start time may be specified as: + M-bM-^@M-M-bM-^@M-" The string M-bM-^@M-^\alwaysM-bM-^@M-^] to indicate the certificate has no + specified start time. + M-bM-^@M-M-bM-^@M-" A date or time in the system time zone formatted as YYYYMMDD + or YYYYMMDDHHMM[SS]. + M-bM-^@M-M-bM-^@M-" A date or time in the UTC time zone as YYYYMMDDZ or + YYYYMMDDHHMM[SS]Z. + M-bM-^@M-M-bM-^@M-" A relative time before the current system time consisting of + a minus sign followed by an interval in the format described + in the TIME FORMATS section of sshd_config(5). + M-bM-^@M-M-bM-^@M-" A raw seconds since epoch (Jan 1 1970 00:00:00 UTC) as a + hexadecimal number beginning with M-bM-^@M-^\0xM-bM-^@M-^]. + + The end time may be specified similarly to the start time: + M-bM-^@M-M-bM-^@M-" The string M-bM-^@M-^\foreverM-bM-^@M-^] to indicate the certificate has no + specified end time. + M-bM-^@M-M-bM-^@M-" A date or time in the system time zone formatted as YYYYMMDD + or YYYYMMDDHHMM[SS]. + M-bM-^@M-M-bM-^@M-" A date or time in the UTC time zone as YYYYMMDDZ or + YYYYMMDDHHMM[SS]Z. + M-bM-^@M-M-bM-^@M-" A relative time after the current system time consisting of a + plus sign followed by an interval in the format described in + the TIME FORMATS section of sshd_config(5). + M-bM-^@M-M-bM-^@M-" A raw seconds since epoch (Jan 1 1970 00:00:00 UTC) as a + hexadecimal number beginning with M-bM-^@M-^\0xM-bM-^@M-^]. + + For example: + + +52w1d Valid from now to 52 weeks and one day from now. + + -4w:+4w + Valid from four weeks ago to four weeks from now. + + 20100101123000:20110101123000 + Valid from 12:30 PM, January 1st, 2010 to 12:30 PM, + January 1st, 2011. + + 20100101123000Z:20110101123000Z + Similar, but interpreted in the UTC time zone rather than + the system time zone. + + -1d:20110101 + Valid from yesterday to midnight, January 1st, 2011. + + 0x1:0x2000000000 + Valid from roughly early 1970 to May 2033. + + -1m:forever + Valid from one minute ago and never expiring. + + -v Verbose mode. Causes ssh-keygen to print debugging messages + about its progress. This is helpful for debugging moduli + generation. Multiple -v options increase the verbosity. The + maximum is 3. + + -w provider + Specifies a path to a library that will be used when creating + FIDO authenticator-hosted keys, overriding the default of using + the internal USB HID support. + + -Y find-principals + Find the principal(s) associated with the public key of a + signature, provided using the -s flag in an authorized signers + file provided using the -f flag. The format of the allowed + signers file is documented in the ALLOWED SIGNERS section below. + If one or more matching principals are found, they are returned + on standard output. + + -Y match-principals + Find principal matching the principal name provided using the -I + flag in the authorized signers file specified using the -f flag. + If one or more matching principals are found, they are returned + on standard output. + + -Y check-novalidate + Checks that a signature generated using ssh-keygen -Y sign has a + valid structure. This does not validate if a signature comes + from an authorized signer. When testing a signature, ssh-keygen + accepts a message on standard input and a signature namespace + using -n. A file containing the corresponding signature must + also be supplied using the -s flag. Successful testing of the + signature is signalled by ssh-keygen returning a zero exit + status. + + -Y sign + Cryptographically sign a file or some data using an SSH key. + When signing, ssh-keygen accepts zero or more files to sign on + the command-line - if no files are specified then ssh-keygen will + sign data presented on standard input. Signatures are written to + the path of the input file with M-bM-^@M-^\.sigM-bM-^@M-^] appended, or to standard + output if the message to be signed was read from standard input. + + The key used for signing is specified using the -f option and may + refer to either a private key, or a public key with the private + half available via ssh-agent(1). An additional signature + namespace, used to prevent signature confusion across different + domains of use (e.g. file signing vs email signing) must be + provided via the -n flag. Namespaces are arbitrary strings, and + may include: M-bM-^@M-^\fileM-bM-^@M-^] for file signing, M-bM-^@M-^\emailM-bM-^@M-^] for email signing. + For custom uses, it is recommended to use names following a + NAMESPACE@YOUR.DOMAIN pattern to generate unambiguous namespaces. + + -Y verify + Request to verify a signature generated using ssh-keygen -Y sign + as described above. When verifying a signature, ssh-keygen + accepts a message on standard input and a signature namespace + using -n. A file containing the corresponding signature must + also be supplied using the -s flag, along with the identity of + the signer using -I and a list of allowed signers via the -f + flag. The format of the allowed signers file is documented in + the ALLOWED SIGNERS section below. A file containing revoked + keys can be passed using the -r flag. The revocation file may be + a KRL or a one-per-line list of public keys. Successful + verification by an authorized signer is signalled by ssh-keygen + returning a zero exit status. + + -y This option will read a private OpenSSH format file and print an + OpenSSH public key to stdout. + + -Z cipher + Specifies the cipher to use for encryption when writing an + OpenSSH-format private key file. The list of available ciphers + may be obtained using "ssh -Q cipher". The default is + M-bM-^@M-^\aes256-ctrM-bM-^@M-^]. + + -z serial_number + Specifies a serial number to be embedded in the certificate to + distinguish this certificate from others from the same CA. If + the serial_number is prefixed with a M-bM-^@M-^X+M-bM-^@M-^Y character, then the + serial number will be incremented for each certificate signed on + a single command-line. The default serial number is zero. + + When generating a KRL, the -z flag is used to specify a KRL + version number. + +MODULI GENERATION + ssh-keygen may be used to generate groups for the Diffie-Hellman Group + Exchange (DH-GEX) protocol. Generating these groups is a two-step + process: first, candidate primes are generated using a fast, but memory + intensive process. These candidate primes are then tested for + suitability (a CPU-intensive process). + + Generation of primes is performed using the -M generate option. The + desired length of the primes may be specified by the -O bits option. For + example: + + # ssh-keygen -M generate -O bits=2048 moduli-2048.candidates + + By default, the search for primes begins at a random point in the desired + length range. This may be overridden using the -O start option, which + specifies a different start point (in hex). + + Once a set of candidates have been generated, they must be screened for + suitability. This may be performed using the -M screen option. In this + mode ssh-keygen will read candidates from standard input (or a file + specified using the -f option). For example: + + # ssh-keygen -M screen -f moduli-2048.candidates moduli-2048 + + By default, each candidate will be subjected to 100 primality tests. + This may be overridden using the -O prime-tests option. The DH generator + value will be chosen automatically for the prime under consideration. If + a specific generator is desired, it may be requested using the -O + generator option. Valid generator values are 2, 3, and 5. + + Screened DH groups may be installed in /etc/moduli. It is important that + this file contains moduli of a range of bit lengths. + + A number of options are available for moduli generation and screening via + the -O flag: + + lines=number + Exit after screening the specified number of lines while + performing DH candidate screening. + + start-line=line-number + Start screening at the specified line number while performing DH + candidate screening. + + checkpoint=filename + Write the last line processed to the specified file while + performing DH candidate screening. This will be used to skip + lines in the input file that have already been processed if the + job is restarted. + + memory=mbytes + Specify the amount of memory to use (in megabytes) when + generating candidate moduli for DH-GEX. + + start=hex-value + Specify start point (in hex) when generating candidate moduli for + DH-GEX. + + generator=value + Specify desired generator (in decimal) when testing candidate + moduli for DH-GEX. + +CERTIFICATES + ssh-keygen supports signing of keys to produce certificates that may be + used for user or host authentication. Certificates consist of a public + key, some identity information, zero or more principal (user or host) + names and a set of options that are signed by a Certification Authority + (CA) key. Clients or servers may then trust only the CA key and verify + its signature on a certificate rather than trusting many user/host keys. + Note that OpenSSH certificates are a different, and much simpler, format + to the X.509 certificates used in ssl(8). + + ssh-keygen supports two types of certificates: user and host. User + certificates authenticate users to servers, whereas host certificates + authenticate server hosts to users. To generate a user certificate: + + $ ssh-keygen -s /path/to/ca_key -I key_id /path/to/user_key.pub + + The resultant certificate will be placed in /path/to/user_key-cert.pub. + A host certificate requires the -h option: + + $ ssh-keygen -s /path/to/ca_key -I key_id -h /path/to/host_key.pub + + The host certificate will be output to /path/to/host_key-cert.pub. + + It is possible to sign using a CA key stored in a PKCS#11 token by + providing the token library using -D and identifying the CA key by + providing its public half as an argument to -s: + + $ ssh-keygen -s ca_key.pub -D libpkcs11.so -I key_id user_key.pub + + Similarly, it is possible for the CA key to be hosted in a ssh-agent(1). + This is indicated by the -U flag and, again, the CA key must be + identified by its public half. + + $ ssh-keygen -Us ca_key.pub -I key_id user_key.pub + + In all cases, key_id is a "key identifier" that is logged by the server + when the certificate is used for authentication. + + Certificates may be limited to be valid for a set of principal + (user/host) names. By default, generated certificates are valid for all + users or hosts. To generate a certificate for a specified set of + principals: + + $ ssh-keygen -s ca_key -I key_id -n user1,user2 user_key.pub + $ ssh-keygen -s ca_key -I key_id -h -n host.domain host_key.pub + + Additional limitations on the validity and use of user certificates may + be specified through certificate options. A certificate option may + disable features of the SSH session, may be valid only when presented + from particular source addresses or may force the use of a specific + command. + + The options that are valid for user certificates are: + + clear Clear all enabled permissions. This is useful for clearing the + default set of permissions so permissions may be added + individually. + + critical:name[=contents] + extension:name[=contents] + Includes an arbitrary certificate critical option or extension. + The specified name should include a domain suffix, e.g. + M-bM-^@M-^\name@example.comM-bM-^@M-^]. If contents is specified then it is included + as the contents of the extension/option encoded as a string, + otherwise the extension/option is created with no contents + (usually indicating a flag). Extensions may be ignored by a + client or server that does not recognise them, whereas unknown + critical options will cause the certificate to be refused. + + force-command=command + Forces the execution of command instead of any shell or command + specified by the user when the certificate is used for + authentication. + + no-agent-forwarding + Disable ssh-agent(1) forwarding (permitted by default). + + no-port-forwarding + Disable port forwarding (permitted by default). + + no-pty Disable PTY allocation (permitted by default). + + no-user-rc + Disable execution of ~/.ssh/rc by sshd(8) (permitted by default). + + no-x11-forwarding + Disable X11 forwarding (permitted by default). + + permit-agent-forwarding + Allows ssh-agent(1) forwarding. + + permit-port-forwarding + Allows port forwarding. + + permit-pty + Allows PTY allocation. + + permit-user-rc + Allows execution of ~/.ssh/rc by sshd(8). + + permit-X11-forwarding + Allows X11 forwarding. + + no-touch-required + Do not require signatures made using this key include + demonstration of user presence (e.g. by having the user touch the + authenticator). This option only makes sense for the FIDO + authenticator algorithms ecdsa-sk and ed25519-sk. + + source-address=address_list + Restrict the source addresses from which the certificate is + considered valid. The address_list is a comma-separated list of + one or more address/netmask pairs in CIDR format. + + verify-required + Require signatures made using this key indicate that the user was + first verified. This option only makes sense for the FIDO + authenticator algorithms ecdsa-sk and ed25519-sk. Currently PIN + authentication is the only supported verification method, but + other methods may be supported in the future. + + At present, no standard options are valid for host keys. + + Finally, certificates may be defined with a validity lifetime. The -V + option allows specification of certificate start and end times. A + certificate that is presented at a time outside this range will not be + considered valid. By default, certificates are valid from the UNIX Epoch + to the distant future. + + For certificates to be used for user or host authentication, the CA + public key must be trusted by sshd(8) or ssh(1). Refer to those manual + pages for details. + +FIDO AUTHENTICATOR + ssh-keygen is able to generate FIDO authenticator-backed keys, after + which they may be used much like any other key type supported by OpenSSH, + so long as the hardware authenticator is attached when the keys are used. + FIDO authenticators generally require the user to explicitly authorise + operations by touching or tapping them. FIDO keys consist of two parts: + a key handle part stored in the private key file on disk, and a per- + device private key that is unique to each FIDO authenticator and that + cannot be exported from the authenticator hardware. These are combined + by the hardware at authentication time to derive the real key that is + used to sign authentication challenges. Supported key types are ecdsa-sk + and ed25519-sk. + + The options that are valid for FIDO keys are: + + application + Override the default FIDO application/origin string of M-bM-^@M-^\ssh:M-bM-^@M-^]. + This may be useful when generating host or domain-specific + resident keys. The specified application string must begin with + M-bM-^@M-^\ssh:M-bM-^@M-^]. + + challenge=path + Specifies a path to a challenge string that will be passed to the + FIDO authenticator during key generation. The challenge string + may be used as part of an out-of-band protocol for key enrollment + (a random challenge is used by default). + + device Explicitly specify a fido(4) device to use, rather than letting + the authenticator middleware select one. + + no-touch-required + Indicate that the generated private key should not require touch + events (user presence) when making signatures. Note that sshd(8) + will refuse such signatures by default, unless overridden via an + authorized_keys option. + + resident + Indicate that the key handle should be stored on the FIDO + authenticator itself. This makes it easier to use the + authenticator on multiple computers. Resident keys may be + supported on FIDO2 authenticators and typically require that a + PIN be set on the authenticator prior to generation. Resident + keys may be loaded off the authenticator using ssh-add(1). + Storing both parts of a key on a FIDO authenticator increases the + likelihood of an attacker being able to use a stolen + authenticator device. + + user A username to be associated with a resident key, overriding the + empty default username. Specifying a username may be useful when + generating multiple resident keys for the same application name. + + verify-required + Indicate that this private key should require user verification + for each signature. Not all FIDO authenticators support this + option. Currently PIN authentication is the only supported + verification method, but other methods may be supported in the + future. + + write-attestation=path + May be used at key generation time to record the attestation data + returned from FIDO authenticators during key generation. This + information is potentially sensitive. By default, this + information is discarded. + +KEY REVOCATION LISTS + ssh-keygen is able to manage OpenSSH format Key Revocation Lists (KRLs). + These binary files specify keys or certificates to be revoked using a + compact format, taking as little as one bit per certificate if they are + being revoked by serial number. + + KRLs may be generated using the -k flag. This option reads one or more + files from the command line and generates a new KRL. The files may + either contain a KRL specification (see below) or public keys, listed one + per line. Plain public keys are revoked by listing their hash or + contents in the KRL and certificates revoked by serial number or key ID + (if the serial is zero or not available). + + Revoking keys using a KRL specification offers explicit control over the + types of record used to revoke keys and may be used to directly revoke + certificates by serial number or key ID without having the complete + original certificate on hand. A KRL specification consists of lines + containing one of the following directives followed by a colon and some + directive-specific information. + + serial: serial_number[-serial_number] + Revokes a certificate with the specified serial number. Serial + numbers are 64-bit values, not including zero and may be + expressed in decimal, hex or octal. If two serial numbers are + specified separated by a hyphen, then the range of serial numbers + including and between each is revoked. The CA key must have been + specified on the ssh-keygen command line using the -s option. + + id: key_id + Revokes a certificate with the specified key ID string. The CA + key must have been specified on the ssh-keygen command line using + the -s option. + + key: public_key + Revokes the specified key. If a certificate is listed, then it + is revoked as a plain public key. + + sha1: public_key + Revokes the specified key by including its SHA1 hash in the KRL. + + sha256: public_key + Revokes the specified key by including its SHA256 hash in the + KRL. KRLs that revoke keys by SHA256 hash are not supported by + OpenSSH versions prior to 7.9. + + hash: fingerprint + Revokes a key using a fingerprint hash, as obtained from a + sshd(8) authentication log message or the ssh-keygen -l flag. + Only SHA256 fingerprints are supported here and resultant KRLs + are not supported by OpenSSH versions prior to 7.9. + + KRLs may be updated using the -u flag in addition to -k. When this + option is specified, keys listed via the command line are merged into the + KRL, adding to those already there. + + It is also possible, given a KRL, to test whether it revokes a particular + key (or keys). The -Q flag will query an existing KRL, testing each key + specified on the command line. If any key listed on the command line has + been revoked (or an error encountered) then ssh-keygen will exit with a + non-zero exit status. A zero exit status will only be returned if no key + was revoked. + +ALLOWED SIGNERS + When verifying signatures, ssh-keygen uses a simple list of identities + and keys to determine whether a signature comes from an authorized + source. This "allowed signers" file uses a format patterned after the + AUTHORIZED_KEYS FILE FORMAT described in sshd(8). Each line of the file + contains the following space-separated fields: principals, options, + keytype, base64-encoded key. Empty lines and lines starting with a M-bM-^@M-^X#M-bM-^@M-^Y + are ignored as comments. + + The principals field is a pattern-list (see PATTERNS in ssh_config(5)) + consisting of one or more comma-separated USER@DOMAIN identity patterns + that are accepted for signing. When verifying, the identity presented + via the -I option must match a principals pattern in order for the + corresponding key to be considered acceptable for verification. + + The options (if present) consist of comma-separated option + specifications. No spaces are permitted, except within double quotes. + The following option specifications are supported (note that option + keywords are case-insensitive): + + cert-authority + Indicates that this key is accepted as a certificate authority + (CA) and that certificates signed by this CA may be accepted for + verification. + + namespaces=namespace-list + Specifies a pattern-list of namespaces that are accepted for this + key. If this option is present, the signature namespace embedded + in the signature object and presented on the verification + command-line must match the specified list before the key will be + considered acceptable. + + valid-after=timestamp + Indicates that the key is valid for use at or after the specified + timestamp, which may be a date or time in the YYYYMMDD[Z] or + YYYYMMDDHHMM[SS][Z] formats. Dates and times will be interpreted + in the current system time zone unless suffixed with a Z + character, which causes them to be interpreted in the UTC time + zone. + + valid-before=timestamp + Indicates that the key is valid for use at or before the + specified timestamp. + + When verifying signatures made by certificates, the expected principal + name must match both the principals pattern in the allowed signers file + and the principals embedded in the certificate itself. + + An example allowed signers file: + + # Comments allowed at start of line + user1@example.com,user2@example.com ssh-rsa AAAAX1... + # A certificate authority, trusted for all principals in a domain. + *@example.com cert-authority ssh-ed25519 AAAB4... + # A key that is accepted only for file signing. + user2@example.com namespaces="file" ssh-ed25519 AAA41... + +ENVIRONMENT + 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. + +FILES + ~/.ssh/id_dsa + ~/.ssh/id_ecdsa + ~/.ssh/id_ecdsa_sk + ~/.ssh/id_ed25519 + ~/.ssh/id_ed25519_sk + ~/.ssh/id_rsa + Contains the DSA, ECDSA, authenticator-hosted ECDSA, Ed25519, + authenticator-hosted Ed25519 or RSA authentication identity of + the user. This file should not be readable by anyone but the + user. It is possible to specify a passphrase when generating the + key; that passphrase will be used to encrypt the private part of + this file using 128-bit AES. This file is not automatically + accessed by ssh-keygen but it is offered as the default file for + the private key. ssh(1) will read this file when a login attempt + is made. + + ~/.ssh/id_dsa.pub + ~/.ssh/id_ecdsa.pub + ~/.ssh/id_ecdsa_sk.pub + ~/.ssh/id_ed25519.pub + ~/.ssh/id_ed25519_sk.pub + ~/.ssh/id_rsa.pub + Contains the DSA, ECDSA, authenticator-hosted ECDSA, Ed25519, + authenticator-hosted Ed25519 or RSA public key for + authentication. The contents of this file should be added to + ~/.ssh/authorized_keys on all machines where the user wishes to + log in using public key authentication. There is no need to keep + the contents of this file secret. + + /etc/moduli + Contains Diffie-Hellman groups used for DH-GEX. The file format + is described in moduli(5). + +SEE ALSO + ssh(1), ssh-add(1), ssh-agent(1), moduli(5), sshd(8) + + The Secure Shell (SSH) Public Key File Format, RFC 4716, 2006. + +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. + +OpenBSD 7.3 September 4, 2023 OpenBSD 7.3 |