path: root/usr/src/man/man1/ssh-keygen.1

'\" te
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.\" installed location.
.\" Portions Copyright (c) 2009, Sun Microsystems, Inc. All Rights Reserved.
.TH SSH-KEYGEN 1 "Feb 17, 2009"
.SH NAME
ssh-keygen \- authentication key generation
.SH SYNOPSIS
.LP
.nf
\fBssh-keygen\fR [\fB-q\fR] [\fB-b\fR \fIbits\fR ] \fB-t\fR \fItype\fR [\fB-N\fR \fInew_passphrase\fR]
     [\fB-C\fR \fIcomment\fR] [\fB-f\fR \fIoutput_keyfile\fR]
.fi

.LP
.nf
\fBssh-keygen\fR \fB-p\fR [\fB-P\fR \fIold_passphrase\fR] [\fB-N\fR \fInew_passphrase\fR]
     [\fB-f\fR \fIkeyfile\fR]
.fi

.LP
.nf
\fBssh-keygen\fR \fB-i\fR [\fB-f\fR \fIinput_keyfile\fR]
.fi

.LP
.nf
\fBssh-keygen\fR \fB-e\fR [\fB-f\fR \fIinput_keyfile\fR]
.fi

.LP
.nf
\fBssh-keygen\fR \fB-y\fR [\fB-f\fR \fIinput_keyfile\fR]
.fi

.LP
.nf
\fBssh-keygen\fR \fB-c\fR [\fB-P\fR \fIpassphrase\fR] [\fB-C\fR \fIcomment\fR] [\fB-f\fR \fIkeyfile\fR]
.fi

.LP
.nf
\fBssh-keygen\fR \fB-l\fR [\fB-f\fR \fIinput_keyfile\fR]
.fi

.LP
.nf
\fBssh-keygen\fR \fB-B\fR [\fB-f\fR \fIinput_keyfile\fR]
.fi

.LP
.nf
\fBssh-keygen\fR \fB-F\fR \fIhostname\fR [\fB-f\fR \fIknown_hosts_file\fR]
.fi

.LP
.nf
\fBssh-keygen\fR \fB-H\fR [\fB-f\fR \fIknown_hosts_file\fR]
.fi

.LP
.nf
\fBssh-keygen\fR \fB-R\fR \fIhostname\fR [\fB-f\fR \fIknown_hosts_file\fR]
.fi

.SH DESCRIPTION
.sp
.LP
The \fBssh-keygen\fR utility generates, manages, and converts authentication
keys for \fBssh\fR(1). \fBssh-keygen\fR can create RSA keys for use by SSH
protocol version 1 and RSA or DSA keys for use by SSH protocol version 2. The
type of key to be generated is specified with the \fB-t\fR option.
.sp
.LP
Normally, each user wishing to use \fBSSH\fR with \fBRSA\fR or \fBDSA\fR
authentication runs this once to create the authentication key in
\fB$HOME/.ssh/identity\fR, \fB$HOME/.ssh/id_dsa\fR, or \fB$HOME/.ssh/id_rsa\fR.
The system administrator can also use this to generate host keys..
.sp
.LP
Ordinarily, 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 with the ``\fB\&.pub\fR'' extension appended. The program also asks for a
passphrase. The passphrase can be empty to indicate no passphrase (host keys
must have empty passphrases), or it can be a string of arbitrary length. Good
passphrases are 10-30 characters long, are not simple sentences or otherwise
easy to guess, and contain a mix of uppercase and lowercase letters, numbers,
and non-alphanumeric characters. (English prose has only 1-2 bits of entropy
per word and provides very poor passphrases.) If a passphrase is set, it must
be at least 4 characters long.
.sp
.LP
The passphrase can be changed later by using the \fB-p\fR option.
.sp
.LP
There is no way to recover a lost passphrase. If the passphrase is lost or
forgotten, you have to generate a new key and copy the corresponding public key
to other machines.
.sp
.LP
For \fBRSA\fR, there is also a comment field in the key file that is only for
convenience to the user to help identify the key. The \fIcomment\fR can tell
what the key is for, or whatever is useful. The comment is initialized to
``\fBuser@host\fR'' when the key is created, but can be changed using the
\fB-c\fR option.
.sp
.LP
After a key is generated, instructions below detail where to place the keys to
activate them.
.SH OPTIONS
.sp
.LP
The following options are supported:
.sp
.ne 2
.na
\fB\fB-b\fR \fIbits\fR\fR
.ad
.RS 21n
Specifies the number of bits in the key to create. The minimum number is 512
bits. Generally, 1024 bits is considered sufficient. Key sizes above that no
longer improve security but make things slower. The default is 1024 bits.
.RE

.sp
.ne 2
.na
\fB\fB-B\fR\fR
.ad
.RS 21n
Shows the bubblebabble digest of the specified private or public key file.
.RE

.sp
.ne 2
.na
\fB\fB-c\fR\fR
.ad
.RS 21n
Requests changing the comment in the private and public key files. The program
prompts for the file containing the private keys, for the passphrase if the key
has one, and for the new comment.
.sp
This option only applies to \fBrsa1\fR (\fBSSHv1\fR) keys.
.RE

.sp
.ne 2
.na
\fB\fB-C\fR \fIcomment\fR\fR
.ad
.RS 21n
Provides the new comment.
.RE

.sp
.ne 2
.na
\fB\fB-e\fR\fR
.ad
.RS 21n
This option reads a private or public OpenSSH key file and prints the key in a
"SECSH" Public Key File Format to stdout. This option allows exporting keys for
use by several other SSH implementations.
.RE

.sp
.ne 2
.na
\fB\fB-f\fR\fR
.ad
.RS 21n
Specifies the filename of the key file.
.RE

.sp
.ne 2
.na
\fB\fB-F\fR\fR
.ad
.RS 21n
Search for the specified \fIhostname\fR in a \fBknown_hosts\fR file, listing
any occurrences found. This option is useful to find hashed host names or
addresses and can also be used in conjunction with the \fB-H\fR option to print
found keys in a hashed format.
.RE

.sp
.ne 2
.na
\fB\fB-H\fR\fR
.ad
.RS 21n
Hash a \fBknown_hosts\fR file. This replaces all host names and addresses with
hashed representations within the specified file. The original content is moved
to a file with a \fB\&.old\fR suffix. These hashes may be used normally by
\fBssh\fR and \fBsshd\fR, but they do not reveal identifying information should
the file's contents be disclosed. This option does not modify existing hashed
host names and is therefore safe to use on files that mix hashed and non-hashed
names.
.RE

.sp
.ne 2
.na
\fB\fB-i\fR\fR
.ad
.RS 21n
This option reads an unencrypted private (or public) key file in
SSH2-compatible format and prints an OpenSSH compatible private (or public) key
to stdout. \fBssh-keygen\fR also reads the "SECSH" Public Key File Format. This
option allows importing keys from several other SSH implementations.
.RE

.sp
.ne 2
.na
\fB\fB-l\fR\fR
.ad
.RS 21n
Shows the fingerprint of the specified private or public key file.
.RE

.sp
.ne 2
.na
\fB\fB-N\fR \fInew_passphrase\fR\fR
.ad
.RS 21n
Provides the new passphrase.
.RE

.sp
.ne 2
.na
\fB\fB-p\fR\fR
.ad
.RS 21n
Requests changing the passphrase of a private key file instead of creating a
new private key. The program prompts for the file containing the private key,
for the old passphrase, and prompts twice for the new passphrase.
.RE

.sp
.ne 2
.na
\fB\fB-P\fR \fIpassphrase\fR\fR
.ad
.RS 21n
Provides the (old) passphrase.
.RE

.sp
.ne 2
.na
\fB\fB-q\fR\fR
.ad
.RS 21n
Silences \fBssh-keygen\fR.
.RE

.sp
.ne 2
.na
\fB\fB-t\fR \fItype\fR\fR
.ad
.RS 21n
Specifies the algorithm used for the key, where \fItype\fR is one of \fBrsa\fR,
\fBdsa\fR, and \fBrsa1\fR. Type \fBrsa1\fR is used only for the SSHv1 protocol.
.RE

.sp
.ne 2
.na
\fB\fB-R\fR \fIhostname\fR\fR
.ad
.RS 21n
Removes all keys belonging to \fIhostname\fR from a \fBknown_hosts\fR file.
This option is useful to delete hashed hosts. See \fB-H\fR.
.RE

.sp
.ne 2
.na
\fB\fB-x\fR\fR
.ad
.RS 21n
Obsolete. Replaced by the \fB-e\fR option.
.RE

.sp
.ne 2
.na
\fB\fB-X\fR\fR
.ad
.RS 21n
Obsolete. Replaced by the \fB-i\fR option.
.RE

.sp
.ne 2
.na
\fB\fB-y\fR\fR
.ad
.RS 21n
This option reads a private OpenSSH format file and prints an OpenSSH public
key to stdout.
.RE

.SH EXIT STATUS
.sp
.LP
The following exit values are returned:
.sp
.ne 2
.na
\fB\fB0\fR\fR
.ad
.RS 5n
Successful completion.
.RE

.sp
.ne 2
.na
\fB\fB1\fR\fR
.ad
.RS 5n
An error occurred.
.RE

.SH FILES
.sp
.ne 2
.na
\fB\fB$HOME/.ssh/identity\fR\fR
.ad
.RS 27n
This file contains the RSA private key for the SSHv1 protocol. This file should
not be readable by anyone but the user. It is possible to specify a passphrase
when generating the key; that passphrase is used to encrypt the private part of
this file using 3DES. This file is not automatically accessed by
\fBssh-keygen\fR, but it is offered as the default file for the private key.
\fBsshd\fR(1M) reads this file when a login attempt is made.
.RE

.sp
.ne 2
.na
\fB\fB$HOME/.ssh/identity.pub\fR\fR
.ad
.RS 27n
This file contains the RSA public key for the SSHv1 protocol. The contents of
this file should be added to \fB$HOME/.ssh/authorized_keys\fR on all machines
where you wish to log in using \fBRSA\fR authentication. There is no need to
keep the contents of this file secret.
.RE

.sp
.ne 2
.na
\fB\fB$HOME/.ssh/id_dsa\fR\fR
.ad
.br
.na
\fB\fB$HOME/.ssh/id_rsa\fR\fR
.ad
.RS 27n
These files contain, respectively, the DSA or RSA private key for the SSHv2
protocol. These files should not be readable by anyone but the user. It is
possible to specify a passphrase when generating the key; that passphrase is
used to encrypt the private part of the file using 3DES. Neither of these files
is automatically accessed by \fBssh-keygen\fR but is offered as the default
file for the private key. \fBsshd\fR(1M) reads this file when a login attempt
is made.
.RE

.sp
.ne 2
.na
\fB\fB$HOME/.ssh/id_dsa.pub\fR\fR
.ad
.br
.na
\fB\fB$HOME/.ssh/id_rsa.pub\fR\fR
.ad
.RS 27n
These files contain, respectively, the DSA or RSA public key for the SSHv2
protocol. The contents of these files should be added, respectively, to
\fB$HOME/.ssh/authorized_keys\fR on all machines where you wish to log in using
DSA or RSA authentication. There is no need to keep the contents of these files
secret.
.RE

.SH ATTRIBUTES
.sp
.LP
See \fBattributes\fR(5) for descriptions of the following attributes:
.sp

.sp
.TS
box;
c | c
l | l .
ATTRIBUTE TYPE	ATTRIBUTE VALUE
_
Interface Stability	Committed
.TE

.SH SEE ALSO
.sp
.LP
\fBssh\fR(1), \fBssh-add\fR(1), \fBssh-agent\fR(1), \fBsshd\fR(1M),
\fBattributes\fR(5)