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162 lines
4.6 KiB
Groff
162 lines
4.6 KiB
Groff
.\" -*- nroff -*-
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.\"
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.\" ssh-keygen.1
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.\"
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.\" Author: Tatu Ylonen <ylo@cs.hut.fi>
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.\"
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.\" Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
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.\" All rights reserved
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.\"
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.\" Created: Sat Apr 22 23:55:14 1995 ylo
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.\"
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.\" $Id: ssh-keygen.1,v 1.9 2000/01/22 08:57:40 damien Exp $
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.\"
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.Dd September 25, 1999
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.Dt SSH-KEYGEN 1
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.Os
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.Sh NAME
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.Nm ssh-keygen
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.Nd authentication key generation
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.Sh SYNOPSIS
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.Nm ssh-keygen
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.Op Fl q
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.Op Fl b Ar bits
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.Op Fl N Ar new_passphrase
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.Op Fl C Ar comment
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.Op Fl f Ar keyfile
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.Nm ssh-keygen
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.Fl p
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.Op Fl P Ar old_passphrase
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.Op Fl N Ar new_passphrase
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.Op Fl f Ar keyfile
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.Nm ssh-keygen
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.Fl c
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.Op Fl P Ar passphrase
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.Op Fl C Ar comment
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.Op Fl f Ar keyfile
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.Nm ssh-keygen
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.Fl l
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.Op Fl f Ar keyfile
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.Sh DESCRIPTION
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.Nm
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generates and manages authentication keys for
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.Xr ssh 1 .
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Normally each user wishing to use SSH
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with RSA authentication runs this once to create the authentication
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key in
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.Pa $HOME/.ssh/identity .
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Additionally, the system administrator may use this to generate host keys.
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.Pp
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Normally this program generates the key and asks for a file in which
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to store the private key. The public key is stored in a file with the
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same name but
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.Dq .pub
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appended. The program also asks for a
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passphrase. The passphrase may be empty to indicate no passphrase
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(host keys must have empty passphrase), or it may be a string of
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arbitrary length. Good passphrases are 10-30 characters long and are
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not simple sentences or otherwise easily guessable (English
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prose has only 1-2 bits of entropy per word, and provides very bad
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passphrases). The passphrase can be changed later by using the
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.Fl p
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option.
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.Pp
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There is no way to recover a lost passphrase. If the passphrase is
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lost or forgotten, you will have to generate a new key and copy the
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corresponding public key to other machines.
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.Pp
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There is also a comment field in the key file that is only for
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convenience to the user to help identify the key. The comment can
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tell what the key is for, or whatever is useful. The comment is
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initialized to
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.Dq user@host
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when the key is created, but can be changed using the
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.Fl c
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option.
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.Pp
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The options are as follows:
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.Bl -tag -width Ds
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.It Fl b Ar bits
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Specifies the number of bits in the key to create. Minimum is 512
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bits. Generally 1024 bits is considered sufficient, and key sizes
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above that no longer improve security but make things slower. The
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default is 1024 bits.
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.It Fl c
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Requests changing the comment in the private and public key files.
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The program will prompt for the file containing the private keys, for
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passphrase if the key has one, and for the new comment.
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.It Fl f
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Specifies the filename of the key file.
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.It Fl l
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Show fingerprint of specified private or public key file.
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.It Fl p
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Requests changing the passphrase of a private key file instead of
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creating a new private key. The program will prompt for the file
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containing the private key, for the old passphrase, and twice for the
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new passphrase.
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.It Fl q
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Silence
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.Nm ssh-keygen .
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Used by
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.Pa /etc/rc
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when creating a new key.
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.It Fl C Ar comment
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Provides the new comment.
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.It Fl N Ar new_passphrase
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Provides the new passphrase.
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.It Fl P Ar passphrase
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Provides the (old) passphrase.
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.El
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.Sh FILES
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.Bl -tag -width Ds
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.It Pa $HOME/.ssh/identity
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Contains the RSA authentication identity of the user. This file
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should not be readable by anyone but the user. It is possible to
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specify a passphrase when generating the key; that passphrase will be
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used to encrypt the private part of this file using 3DES. This file
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is not automatically accessed by
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.Nm
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but it is offered as the default file for the private key.
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.It Pa $HOME/.ssh/identity.pub
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Contains the public key for authentication. The contents of this file
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should be added to
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.Pa $HOME/.ssh/authorized_keys
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on all machines
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where you wish to log in using RSA authentication. There is no
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need to keep the contents of this file secret.
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.Sh AUTHOR
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Tatu Ylonen <ylo@cs.hut.fi>
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.Pp
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OpenSSH
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is a derivative of the original (free) ssh 1.2.12 release, but with bugs
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removed and newer features re-added. Rapidly after the 1.2.12 release,
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newer versions bore successively more restrictive licenses. This version
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of OpenSSH
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.Bl -bullet
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.It
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has all components of a restrictive nature (i.e., patents, see
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.Xr ssl 8 )
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directly removed from the source code; any licensed or patented components
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are chosen from
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external libraries.
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.It
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has been updated to support ssh protocol 1.5.
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.It
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contains added support for
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.Xr kerberos 8
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authentication and ticket passing.
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.It
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supports one-time password authentication with
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.Xr skey 1 .
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.El
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.Pp
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The libraries described in
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.Xr ssl 8
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are required for proper operation.
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.Sh SEE ALSO
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.Xr ssh 1 ,
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.Xr ssh-add 1 ,
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.Xr ssh-agent 1 ,
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.Xr sshd 8 ,
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.Xr ssl 8
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