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NAME | SYNOPSIS | DESCRIPTION | MODULI GENERATION | CERTIFICATES | KEY REVOCATION LISTS | ALLOWED SIGNERS | ENVIRONMENT | FILES | SEE ALSO | AUTHORS | COLOPHON |
SSH-KEYGEN(1) BSD General Commands Manual SSH-KEYGEN(1)
ssh-keygen — OpenSSH authentication key utility
ssh-keygen [-q] [-b bits] [-C comment] [-f output_keyfile] [-m format]
[-t dsa | ecdsa | ecdsa-sk | ed25519 | ed25519-sk | rsa]
[-N new_passphrase] [-O option] [-w provider]
ssh-keygen -p [-f keyfile] [-m format] [-N new_passphrase]
[-P old_passphrase]
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 [-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 [-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 [-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 -s signature_file -f allowed_signers_file
ssh-keygen -Y check-novalidate -n namespace -s signature_file
ssh-keygen -Y sign -f key_file -n namespace file ...
ssh-keygen -Y verify -f allowed_signers_file -I signer_identity -n
namespace -s signature_file [-r revocation_file]
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 RSA 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Lists, and to test whether given keys have been revoked by one.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 admin‐
istrator 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 “.pub” 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, num‐
bers, 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 “user@host” 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 generat‐
ing 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, instructions below detail where the keys
should be placed to be activated.
The options are as follows:
-A For each of the key types (rsa, dsa, ecdsa and ed25519) for
which host keys do not exist, generate the host keys with the
default key file path, an empty passphrase, default bits for
the key type, and default comment. If -f has also been speci‐
fied, its argument is used as a prefix to the default path for
the resulting host key files. This is used by /etc/rc to gen‐
erate new host keys.
-a rounds
When saving a private key, this option specifies the number of
KDF (key derivation function) rounds used. Higher numbers
result in slower passphrase verification and increased resis‐
tance to brute-force password cracking (should the keys be
stolen).
-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 indi‐
cates 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 finger‐
prints. Valid options are: “md5” and “sha256”. The default is
“sha256”.
-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 “RFC4716”. 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 suf‐
fix. 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. Please see the CERTIFICATES section for details.
-I certificate_identity
Specify the key identity when signing a public key. Please 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 “RFC4716”.
-K Download resident keys from a FIDO authenticator. Public and
private key files will be written to the current directory for
each downloaded key.
-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
‘diffie-hellman-group-exchange-*’ key exchange methods. The
numbers generated by this operation must be further screened
before use. See the MODULI GENERATION section for more infor‐
mation.
-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 genera‐
tors. 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 oper‐
ation. The latter may be used to convert between OpenSSH pri‐
vate key and PEM private key formats. The supported key for‐
mats are: “RFC4716” (RFC 4716/SSH2 public or private key),
“PKCS8” (PKCS8 public or private key) or “PEM” (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 “RFC4716”. Setting a format of
“PEM” 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 princi‐
pals may be specified, separated by commas. Please see the
CERTIFICATES section for details.
-O option
Specify a key/value option. These are specific to the opera‐
tion 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 speci‐
fied.
When generating a key that will be hosted on a FIDO authentica‐
tor, this flag may be used to specify key-specific options.
Those supported at present are:
application
Override the default FIDO application/origin string of
“ssh:”. This may be useful when generating host or
domain-specific resident keys. The specified applica‐
tion string must begin with “ssh:”.
challenge=path
Specifies a path to a challenge string that will be
passed to the FIDO token 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 token middleware select one.
no-touch-required
Indicate that the generated private key should not
require touch events (user presence) when making signa‐
tures. Note that sshd(8) will refuse such signatures
by default, unless overridden via an authorized_keys
option.
resident
Indicate that the key should be stored on the FIDO
authenticator itself. Resident keys may be supported
on FIDO2 tokens and typically require that a PIN be set
on the token prior to generation. Resident keys may be
loaded off the token using ssh-add(1).
user A username to be associated with a resident key, over‐
riding the empty default username. Specifying a user‐
name may be useful when generating multiple resident
keys for the same application name.
write-attestation=path
May be used at key generation time to record the attes‐
tation certificate returned from FIDO tokens during key
generation. By default this information is discarded.
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. Please
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
“dsa”, “ecdsa”, “ecdsa-sk”, “ed25519”, “ed25519-sk”, or “rsa”.
This flag may also be used to specify the desired signature
type when signing certificates using an RSA CA key. The avail‐
able RSA signature variants are “ssh-rsa” (SHA1 signatures, not
recommended), “rsa-sha2-256”, and “rsa-sha2-512” (the default).
-U When used in combination with -s, 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 com‐
mand 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 indi‐
cate an explicit time interval.
The start time may be specified as the string “always” to indi‐
cate the certificate has no specified start time, a date in
YYYYMMDD format, a time in YYYYMMDDHHMM[SS] format, a relative
time (to the current time) consisting of a minus sign followed
by an interval in the format described in the TIME FORMATS sec‐
tion of sshd_config(5).
The end time may be specified as a YYYYMMDD date, a YYYYMMD‐
DHHMM[SS] time, a relative time starting with a plus character
or the string “forever” to indicate that the certificate has no
expiry date.
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),
“-1d:20110101” (valid from yesterday to midnight, January 1st,
2011). “-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 gen‐
eration. Multiple -v options increase the verbosity. The max‐
imum 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 sig‐
nature, 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 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 signa‐
ture must also be supplied using the -s flag. Successful test‐
ing of the signature is signalled by ssh-keygen returning a
zero exit status.
-Y sign
Cryptographically sign a file or some data using a 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 “.sig” 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 signa‐
ture namespace, used to prevent signature confusion across dif‐
ferent domains of use (e.g. file signing vs email signing) must
be provided via the -n flag. Namespaces are arbitrary strings,
and may include: “file” for file signing, “email” for email
signing. For custom uses, it is recommended to use names fol‐
lowing 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 signa‐
ture 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 con‐
taining 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 sig‐
nalled 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 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 ‘+’ 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.
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 suit‐
ability (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 genera‐
tor value will be chosen automatically for the prime under considera‐
tion. 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 and that both
ends of a connection share common moduli.
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 per‐
forming 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 per‐
forming 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 gener‐
ating 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.
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 sim‐
pler, 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 pro‐
viding the token library using -D and identifying the CA key by provid‐
ing 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 individ‐
ually.
critical:name[=contents]
extension:name[=contents]
Includes an arbitrary certificate critical option or extension.
The specified name should include a domain suffix, e.g.
“name@example.com”. 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 con‐
tents (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 authen‐
tication.
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 require demon‐
stration 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.
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 cer‐
tificate that is presented at a time outside this range will not be
considered valid. By default, certificates are valid from 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). Please refer to those
manual pages for details.
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 com‐
plete 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 num‐
bers 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 particu‐
lar 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 com‐
mand 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.
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 ‘#’ 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 cor‐
responding key to be considered acceptable for verification.
The options (if present) consist of comma-separated option specifica‐
tions. No spaces are permitted, except within double quotes. The fol‐
lowing 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 verifica‐
tion command-line must match the specified list before the key
will be considered acceptable.
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...
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.
~/.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 automat‐
ically 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 authentica‐
tion. 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 for‐
mat is described in moduli(5).
ssh(1), ssh-add(1), ssh-agent(1), moduli(5), sshd(8)
The Secure Shell (SSH) Public Key File Format, RFC 4716, 2006.
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.
This page is part of the openssh (Portable OpenSSH) project. Informa‐
tion about the project can be found at
http://www.openssh.com/portable.html. If you have a bug report for
this manual page, see ⟨http://www.openssh.com/report.html⟩. This page
was obtained from the tarball openssh-8.3p1.tar.gz fetched from
⟨http://ftp.eu.openbsd.org/pub/OpenBSD/OpenSSH/portable/⟩ on
2020-08-13. If you discover any rendering problems in this HTML ver‐
sion of the page, or you believe there is a better or more up-to-date
source for the page, or you have corrections or improvements to the
information in this COLOPHON (which is not part of the original manual
page), send a mail to man-pages@man7.org
BSD April 3, 2020 BSD