161 lines
3.8 KiB
Groff
161 lines
3.8 KiB
Groff
.\" $OpenBSD: ssh-keyscan.1,v 1.15 2003/03/28 10:11:43 jmc Exp $
|
|
.\"
|
|
.\" Copyright 1995, 1996 by David Mazieres <dm@lcs.mit.edu>.
|
|
.\"
|
|
.\" Modification and redistribution in source and binary forms is
|
|
.\" permitted provided that due credit is given to the author and the
|
|
.\" OpenBSD project by leaving this copyright notice intact.
|
|
.\"
|
|
.Dd January 1, 1996
|
|
.Dt SSH-KEYSCAN 1
|
|
.Os
|
|
.Sh NAME
|
|
.Nm ssh-keyscan
|
|
.Nd gather ssh public keys
|
|
.Sh SYNOPSIS
|
|
.Nm ssh-keyscan
|
|
.Bk -words
|
|
.Op Fl v46
|
|
.Op Fl p Ar port
|
|
.Op Fl T Ar timeout
|
|
.Op Fl t Ar type
|
|
.Op Fl f Ar file
|
|
.Op Ar host | addrlist namelist
|
|
.Op Ar ...
|
|
.Ek
|
|
.Sh DESCRIPTION
|
|
.Nm
|
|
is a utility for gathering the public ssh host keys of a number of
|
|
hosts.
|
|
It was designed to aid in building and verifying
|
|
.Pa ssh_known_hosts
|
|
files.
|
|
.Nm
|
|
provides a minimal interface suitable for use by shell and perl
|
|
scripts.
|
|
.Pp
|
|
.Nm
|
|
uses non-blocking socket I/O to contact as many hosts as possible in
|
|
parallel, so it is very efficient.
|
|
The keys from a domain of 1,000
|
|
hosts can be collected in tens of seconds, even when some of those
|
|
hosts are down or do not run ssh.
|
|
For scanning, one does not need
|
|
login access to the machines that are being scanned, nor does the
|
|
scanning process involve any encryption.
|
|
.Pp
|
|
The options are as follows:
|
|
.Bl -tag -width Ds
|
|
.It Fl p Ar port
|
|
Port to connect to on the remote host.
|
|
.It Fl T Ar timeout
|
|
Set the timeout for connection attempts.
|
|
If
|
|
.Pa timeout
|
|
seconds have elapsed since a connection was initiated to a host or since the
|
|
last time anything was read from that host, then the connection is
|
|
closed and the host in question considered unavailable.
|
|
Default is 5 seconds.
|
|
.It Fl t Ar type
|
|
Specifies the type of the key to fetch from the scanned hosts.
|
|
The possible values are
|
|
.Dq rsa1
|
|
for protocol version 1 and
|
|
.Dq rsa
|
|
or
|
|
.Dq dsa
|
|
for protocol version 2.
|
|
Multiple values may be specified by separating them with commas.
|
|
The default is
|
|
.Dq rsa1 .
|
|
.It Fl f Ar filename
|
|
Read hosts or
|
|
.Pa addrlist namelist
|
|
pairs from this file, one per line.
|
|
If
|
|
.Pa -
|
|
is supplied instead of a filename,
|
|
.Nm
|
|
will read hosts or
|
|
.Pa addrlist namelist
|
|
pairs from the standard input.
|
|
.It Fl v
|
|
Verbose mode.
|
|
Causes
|
|
.Nm
|
|
to print debugging messages about its progress.
|
|
.It Fl 4
|
|
Forces
|
|
.Nm
|
|
to use IPv4 addresses only.
|
|
.It Fl 6
|
|
Forces
|
|
.Nm
|
|
to use IPv6 addresses only.
|
|
.El
|
|
.Sh SECURITY
|
|
If a ssh_known_hosts file is constructed using
|
|
.Nm
|
|
without verifying the keys, users will be vulnerable to
|
|
.I man in the middle
|
|
attacks.
|
|
On the other hand, if the security model allows such a risk,
|
|
.Nm
|
|
can help in the detection of tampered keyfiles or man in the middle
|
|
attacks which have begun after the ssh_known_hosts file was created.
|
|
.Sh EXAMPLES
|
|
.Pp
|
|
Print the
|
|
.Pa rsa1
|
|
host key for machine
|
|
.Pa hostname :
|
|
.Bd -literal
|
|
$ ssh-keyscan hostname
|
|
.Ed
|
|
.Pp
|
|
Find all hosts from the file
|
|
.Pa ssh_hosts
|
|
which have new or different keys from those in the sorted file
|
|
.Pa ssh_known_hosts :
|
|
.Bd -literal
|
|
$ ssh-keyscan -t rsa,dsa -f ssh_hosts | \e\
|
|
sort -u - ssh_known_hosts | diff ssh_known_hosts -
|
|
.Ed
|
|
.Sh FILES
|
|
.Pa Input format:
|
|
.Bd -literal
|
|
1.2.3.4,1.2.4.4 name.my.domain,name,n.my.domain,n,1.2.3.4,1.2.4.4
|
|
.Ed
|
|
.Pp
|
|
.Pa Output format for rsa1 keys:
|
|
.Bd -literal
|
|
host-or-namelist bits exponent modulus
|
|
.Ed
|
|
.Pp
|
|
.Pa Output format for rsa and dsa keys:
|
|
.Bd -literal
|
|
host-or-namelist keytype base64-encoded-key
|
|
.Ed
|
|
.Pp
|
|
Where
|
|
.Pa keytype
|
|
is either
|
|
.Dq ssh-rsa
|
|
or
|
|
.Dq ssh-dsa .
|
|
.Pp
|
|
.Pa /etc/ssh/ssh_known_hosts
|
|
.Sh BUGS
|
|
It generates "Connection closed by remote host" messages on the consoles
|
|
of all the machines it scans if the server is older than version 2.9.
|
|
This is because it opens a connection to the ssh port, reads the public
|
|
key, and drops the connection as soon as it gets the key.
|
|
.Sh SEE ALSO
|
|
.Xr ssh 1 ,
|
|
.Xr sshd 8
|
|
.Sh AUTHORS
|
|
David Mazieres <dm@lcs.mit.edu>
|
|
wrote the initial version, and
|
|
Wayne Davison <wayned@users.sourceforge.net>
|
|
added support for protocol version 2.
|