227 lines
6.4 KiB
Groff
227 lines
6.4 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 1.18 2000/05/08 17:26:04 hugh 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 dq
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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 x
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.Op Fl f Ar keyfile
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.Nm ssh-keygen
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.Fl X
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.Op Fl f Ar keyfile
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.Nm ssh-keygen
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.Fl y
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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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.Nm ssh-keygen
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.Fl R
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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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.Nm
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defaults to generating an RSA key for use by protocols 1.3 and 1.5;
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specifying the
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.Fl d
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flag will create a DSA key instead for use by protocol 2.0.
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.Pp
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Normally each user wishing to use SSH
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with RSA or DSA 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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or
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.Pa $HOME/.ssh/id_dsa .
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Additionally, the system administrator may use this to generate host keys,
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as seen in
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.Pa /etc/rc .
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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.
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The public key is stored in a file with the same name but
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.Dq .pub
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appended.
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The program also asks for a passphrase.
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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.
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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).
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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.
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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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For RSA, 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.
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The comment can tell what the key is for, or whatever is useful.
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The comment is 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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After a key is generated, instructions below detail where the keys
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should be placed to be activated.
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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.
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Minimum is 512 bits.
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Generally 1024 bits is considered sufficient, and key sizes
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above that no longer improve security but make things slower.
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The 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.
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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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.It Fl R
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If RSA support is functional, immediately exits with code 0. If RSA
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support is not functional, exits with code 1. This flag will be
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removed once the RSA patent expires.
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.It Fl x
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This option will read a private
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OpenSSH DSA format file and print a SSH2-compatible public key to stdout.
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.It Fl X
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This option will read a
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SSH2-compatible public key file and print an OpenSSH DSA compatible public key to stdout.
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.It Fl y
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This option will read a private
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OpenSSH DSA format file and print an OpenSSH DSA public key to stdout.
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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.
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This file should not be readable by anyone but the user.
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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.
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This file 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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.Xr sshd 8
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will read this file when a login attempt is made.
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.It Pa $HOME/.ssh/identity.pub
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Contains the public key for authentication.
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The contents of this file 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.
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There is no need to keep the contents of this file secret.
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.It Pa $HOME/.ssh/id_dsa
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Contains the DSA authentication identity of the user.
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This file should not be readable by anyone but the user.
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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.
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This file 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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.Xr sshd 8
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will read this file when a login attempt is made.
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.It Pa $HOME/.ssh/id_dsa.pub
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Contains the public key for authentication.
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The contents of this file should be added to
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.Pa $HOME/.ssh/authorized_keys2
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on all machines
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where you wish to log in using DSA authentication.
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There is no 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.
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Rapidly after the 1.2.12 release,
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newer versions bore successively more restrictive licenses.
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This version 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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