1 .\" $OpenBSD: ssh-keyscan.1,v 1.17 2003/06/10 09:12:11 jmc Exp $
3 .\" Copyright 1995, 1996 by David Mazieres <dm@lcs.mit.edu>.
5 .\" Modification and redistribution in source and binary forms is
6 .\" permitted provided that due credit is given to the author and the
7 .\" OpenBSD project by leaving this copyright notice intact.
14 .Nd gather ssh public keys
23 .Op Ar host | addrlist namelist
28 is a utility for gathering the public ssh host keys of a number of
30 It was designed to aid in building and verifying
34 provides a minimal interface suitable for use by shell and perl
38 uses non-blocking socket I/O to contact as many hosts as possible in
39 parallel, so it is very efficient.
40 The keys from a domain of 1,000
41 hosts can be collected in tens of seconds, even when some of those
42 hosts are down or do not run ssh.
43 For scanning, one does not need
44 login access to the machines that are being scanned, nor does the
45 scanning process involve any encryption.
47 The options are as follows:
50 Port to connect to on the remote host.
52 Set the timeout for connection attempts.
55 seconds have elapsed since a connection was initiated to a host or since the
56 last time anything was read from that host, then the connection is
57 closed and the host in question considered unavailable.
60 Specifies the type of the key to fetch from the scanned hosts.
61 The possible values are
63 for protocol version 1 and
67 for protocol version 2.
68 Multiple values may be specified by separating them with commas.
74 pairs from this file, one per line.
77 is supplied instead of a filename,
81 pairs from the standard input.
86 to print debugging messages about its progress.
90 to use IPv4 addresses only.
94 to use IPv6 addresses only.
97 If a ssh_known_hosts file is constructed using
99 without verifying the keys, users will be vulnerable to
102 On the other hand, if the security model allows such a risk,
104 can help in the detection of tampered keyfiles or man in the middle
105 attacks which have begun after the ssh_known_hosts file was created.
109 1.2.3.4,1.2.4.4 name.my.domain,name,n.my.domain,n,1.2.3.4,1.2.4.4
112 .Pa Output format for rsa1 keys:
114 host-or-namelist bits exponent modulus
117 .Pa Output format for rsa and dsa keys:
119 host-or-namelist keytype base64-encoded-key
129 .Pa /etc/ssh/ssh_known_hosts
136 $ ssh-keyscan hostname
139 Find all hosts from the file
141 which have new or different keys from those in the sorted file
142 .Pa ssh_known_hosts :
144 $ ssh-keyscan -t rsa,dsa -f ssh_hosts | \e
145 sort -u - ssh_known_hosts | diff ssh_known_hosts -
151 .An David Mazieres Aq dm@lcs.mit.edu
152 wrote the initial version, and
153 .An Wayne Davison Aq wayned@users.sourceforge.net
154 added support for protocol version 2.
156 It generates "Connection closed by remote host" messages on the consoles
157 of all the machines it scans if the server is older than version 2.9.
158 This is because it opens a connection to the ssh port, reads the public
159 key, and drops the connection as soon as it gets the key.