b7aa600c41
I have worked hard to reduce diffs against the vendor branch. One notable change in that respect is that we no longer prefer DSA over RSA - the reasons for doing so went away years ago. This may cause some surprises, as ssh will warn about unknown host keys even for hosts whose keys haven't changed. MFC after: 6 weeks
169 lines
4.0 KiB
Groff
169 lines
4.0 KiB
Groff
.\" $OpenBSD: ssh-keyscan.1,v 1.24 2008/04/30 10:14:03 djm Exp $
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.\"
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.\" Copyright 1995, 1996 by David Mazieres <dm@lcs.mit.edu>.
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.\"
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.\" Modification and redistribution in source and binary forms is
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.\" permitted provided that due credit is given to the author and the
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.\" OpenBSD project by leaving this copyright notice intact.
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.\"
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.Dd $Mdocdate: April 30 2008 $
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.Dt SSH-KEYSCAN 1
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.Os
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.Sh NAME
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.Nm ssh-keyscan
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.Nd gather ssh public keys
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.Sh SYNOPSIS
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.Nm ssh-keyscan
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.Bk -words
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.Op Fl 46Hv
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.Op Fl f Ar file
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.Op Fl p Ar port
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.Op Fl T Ar timeout
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.Op Fl t Ar type
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.Op Ar host | addrlist namelist
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.Op Ar ...
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.Ek
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.Sh DESCRIPTION
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.Nm
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is a utility for gathering the public ssh host keys of a number of
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hosts.
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It was designed to aid in building and verifying
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.Pa ssh_known_hosts
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files.
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.Nm
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provides a minimal interface suitable for use by shell and perl
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scripts.
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.Pp
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.Nm
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uses non-blocking socket I/O to contact as many hosts as possible in
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parallel, so it is very efficient.
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The keys from a domain of 1,000
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hosts can be collected in tens of seconds, even when some of those
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hosts are down or do not run ssh.
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For scanning, one does not need
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login access to the machines that are being scanned, nor does the
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scanning process involve any encryption.
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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 4
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Forces
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.Nm
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to use IPv4 addresses only.
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.It Fl 6
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Forces
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.Nm
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to use IPv6 addresses only.
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.It Fl f Ar file
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Read hosts or
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.Pa addrlist namelist
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pairs from this file, one per line.
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If
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.Pa -
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is supplied instead of a filename,
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.Nm
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will read hosts or
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.Pa addrlist namelist
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pairs from the standard input.
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.It Fl H
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Hash all hostnames and addresses in the output.
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Hashed names may be used normally by
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.Nm ssh
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and
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.Nm sshd ,
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but they do not reveal identifying information should the file's contents
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be disclosed.
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.It Fl p Ar port
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Port to connect to on the remote host.
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.It Fl T Ar timeout
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Set the timeout for connection attempts.
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If
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.Pa timeout
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seconds have elapsed since a connection was initiated to a host or since the
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last time anything was read from that host, then the connection is
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closed and the host in question considered unavailable.
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Default is 5 seconds.
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.It Fl t Ar type
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Specifies the type of the key to fetch from the scanned hosts.
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The possible values are
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.Dq rsa1
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for protocol version 1 and
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.Dq rsa
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or
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.Dq dsa
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for protocol version 2.
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Multiple values may be specified by separating them with commas.
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The default is
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.Dq rsa .
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.It Fl v
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Verbose mode.
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Causes
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.Nm
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to print debugging messages about its progress.
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.El
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.Sh SECURITY
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If an ssh_known_hosts file is constructed using
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.Nm
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without verifying the keys, users will be vulnerable to
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.Em man in the middle
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attacks.
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On the other hand, if the security model allows such a risk,
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.Nm
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can help in the detection of tampered keyfiles or man in the middle
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attacks which have begun after the ssh_known_hosts file was created.
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.Sh FILES
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.Pa Input format:
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.Bd -literal
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1.2.3.4,1.2.4.4 name.my.domain,name,n.my.domain,n,1.2.3.4,1.2.4.4
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.Ed
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.Pp
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.Pa Output format for rsa1 keys:
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.Bd -literal
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host-or-namelist bits exponent modulus
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.Ed
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.Pp
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.Pa Output format for rsa and dsa keys:
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.Bd -literal
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host-or-namelist keytype base64-encoded-key
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.Ed
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.Pp
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Where
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.Pa keytype
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is either
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.Dq ssh-rsa
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or
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.Dq ssh-dss .
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.Pp
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.Pa /etc/ssh/ssh_known_hosts
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.Sh EXAMPLES
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Print the
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.Pa rsa1
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host key for machine
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.Pa hostname :
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.Bd -literal
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$ ssh-keyscan hostname
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.Ed
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.Pp
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Find all hosts from the file
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.Pa ssh_hosts
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which have new or different keys from those in the sorted file
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.Pa ssh_known_hosts :
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.Bd -literal
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$ ssh-keyscan -t rsa,dsa -f ssh_hosts | \e
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sort -u - ssh_known_hosts | diff ssh_known_hosts -
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.Ed
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.Sh SEE ALSO
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.Xr ssh 1 ,
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.Xr sshd 8
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.Sh AUTHORS
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.An -nosplit
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.An David Mazieres Aq dm@lcs.mit.edu
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wrote the initial version, and
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.An Wayne Davison Aq wayned@users.sourceforge.net
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added support for protocol version 2.
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.Sh BUGS
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It generates "Connection closed by remote host" messages on the consoles
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of all the machines it scans if the server is older than version 2.9.
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This is because it opens a connection to the ssh port, reads the public
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key, and drops the connection as soon as it gets the key.
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