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+SSH-KEYGEN(1)               General Commands Manual              SSH-KEYGEN(1)
+
+NAME
+     ssh-keygen M-bM-^@M-^S authentication key generation, management and conversion
+
+SYNOPSIS
+     ssh-keygen [-q] [-b bits] [-C comment] [-f output_keyfile] [-m format]
+                [-N new_passphrase] [-t dsa | ecdsa | ed25519 | rsa]
+     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 -R hostname [-f known_hosts_file]
+     ssh-keygen -r hostname [-g] [-f input_keyfile]
+     ssh-keygen -G output_file [-v] [-b bits] [-M memory] [-S start_point]
+     ssh-keygen -f input_file -T output_file [-v] [-a rounds] [-J num_lines]
+                [-j start_line] [-K checkpt] [-W generator]
+     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 -f krl_file 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]
+
+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 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_ed25519 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, 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 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) rounds used.  Higher numbers result
+             in slower passphrase verification and increased resistance to
+             brute-force password cracking (should the keys be stolen).
+
+             When screening DH-GEX candidates (using the -T command), this
+             option specifies the number of primality tests to perform.
+
+     -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.  Ed25519 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 output_file
+             Generate candidate primes for DH-GEX.  These primes must be
+             screened for safety (using the -T option) before use.
+
+     -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.  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 M-bM-^@M-^\RFC4716M-bM-^@M-^].
+
+     -J num_lines
+             Exit after screening the specified number of lines while
+             performing DH candidate screening using the -T option.
+
+     -j start_line
+             Start screening at the specified line number while performing DH
+             candidate screening using the -T option.
+
+     -K checkpt
+             Write the last line processed to the file checkpt while
+             performing DH candidate screening using the -T option.  This will
+             be used to skip lines in the input file that have already been
+             processed if the job is restarted.
+
+     -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 memory
+             Specify the amount of memory to use (in megabytes) when
+             generating candidate moduli for DH-GEX.
+
+     -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.  Please see the
+             CERTIFICATES section for details.
+
+     -O option
+             Specify a certificate option when signing a key.  This option may
+             be specified multiple times.  See also the CERTIFICATES section
+             for further details.
+
+             At present, no standard options are valid for host keys.  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.
+
+             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.
+
+     -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.
+
+     -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 start
+             Specify start point (in hex) when generating candidate moduli for
+             DH-GEX.
+
+     -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 output_file
+             Test DH group exchange candidate primes (generated using the -G
+             option) for safety.
+
+     -t dsa | ecdsa | ed25519 | 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-^\ed25519M-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, 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 the string M-bM-^@M-^\alwaysM-bM-^@M-^] to
+             indicate 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 section
+             of sshd_config(5).
+
+             The end time may be specified as a YYYYMMDD date, a
+             YYYYMMDDHHMM[SS] time, a relative time starting with a plus
+             character or the string M-bM-^@M-^\foreverM-bM-^@M-^] to indicate that the
+             certificate has no expirty date.
+
+             For example: M-bM-^@M-^\+52w1dM-bM-^@M-^] (valid from now to 52 weeks and one day
+             from now), M-bM-^@M-^\-4w:+4wM-bM-^@M-^] (valid from four weeks ago to four weeks
+             from now), M-bM-^@M-^\20100101123000:20110101123000M-bM-^@M-^] (valid from 12:30 PM,
+             January 1st, 2010 to 12:30 PM, January 1st, 2011), M-bM-^@M-^\-1d:20110101M-bM-^@M-^]
+             (valid from yesterday to midnight, January 1st, 2011).
+             M-bM-^@M-^\-1m:foreverM-bM-^@M-^] (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 generator
+             Specify desired generator when testing candidate moduli for DH-
+             GEX.
+
+     -y      This option will read a private OpenSSH format file and print an
+             OpenSSH public key to stdout.
+
+     -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 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
+
+     -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.
+
+     -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 -G option.  The desired
+     length of the primes may be specified by the -b option.  For example:
+
+           # ssh-keygen -G moduli-2048.candidates -b 2048
+
+     By default, the search for primes begins at a random point in the desired
+     length range.  This may be overridden using the -S 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 -T option.  In this mode
+     ssh-keygen will read candidates from standard input (or a file specified
+     using the -f option).  For example:
+
+           # ssh-keygen -T moduli-2048 -f moduli-2048.candidates
+
+     By default, each candidate will be subjected to 100 primality tests.
+     This may be overridden using the -a 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 -W 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.
+
+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.  For a list of valid certificate options, see the documentation
+     for the -O option above.
+
+     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 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.
+
+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.
+
+     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...
+
+FILES
+     ~/.ssh/id_dsa
+     ~/.ssh/id_ecdsa
+     ~/.ssh/id_ed25519
+     ~/.ssh/id_rsa
+             Contains the DSA, ECDSA, 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_ed25519.pub
+     ~/.ssh/id_rsa.pub
+             Contains the DSA, ECDSA, 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 6.6                     October 3, 2019                    OpenBSD 6.6