1 .\" $OpenBSD: ssh-keyscan.1,v 1.34 2014/01/28 14:13:39 jmc Exp $
4 .\" Copyright 1995, 1996 by David Mazieres <dm@lcs.mit.edu>.
6 .\" Modification and redistribution in source and binary forms is
7 .\" permitted provided that due credit is given to the author and the
8 .\" OpenBSD project by leaving this copyright notice intact.
15 .Nd gather ssh public keys
24 .Op Ar host | addrlist namelist
29 is a utility for gathering the public ssh host keys of a number of
31 It was designed to aid in building and verifying
35 provides a minimal interface suitable for use by shell and perl
39 uses non-blocking socket I/O to contact as many hosts as possible in
40 parallel, so it is very efficient.
41 The keys from a domain of 1,000
42 hosts can be collected in tens of seconds, even when some of those
43 hosts are down or do not run ssh.
44 For scanning, one does not need
45 login access to the machines that are being scanned, nor does the
46 scanning process involve any encryption.
48 The options are as follows:
53 to use IPv4 addresses only.
57 to use IPv6 addresses only.
66 is supplied instead of a filename,
70 pairs from the standard input.
72 Hash all hostnames and addresses in the output.
73 Hashed names may be used normally by
77 but they do not reveal identifying information should the file's contents
80 Port to connect to on the remote host.
82 Set the timeout for connection attempts.
85 seconds have elapsed since a connection was initiated to a host or since the
86 last time anything was read from that host, then the connection is
87 closed and the host in question considered unavailable.
90 Specifies the type of the key to fetch from the scanned hosts.
91 The possible values are
93 for protocol version 1 and
99 for protocol version 2.
100 Multiple values may be specified by separating them with commas.
101 The default is to fetch
110 to print debugging messages about its progress.
113 If an ssh_known_hosts file is constructed using
115 without verifying the keys, users will be vulnerable to
116 .Em man in the middle
118 On the other hand, if the security model allows such a risk,
120 can help in the detection of tampered keyfiles or man in the middle
121 attacks which have begun after the ssh_known_hosts file was created.
125 1.2.3.4,1.2.4.4 name.my.domain,name,n.my.domain,n,1.2.3.4,1.2.4.4
128 Output format for rsa1 keys:
130 host-or-namelist bits exponent modulus
133 Output format for rsa, dsa and ecdsa keys:
135 host-or-namelist keytype base64-encoded-key
141 .Dq ecdsa-sha2-nistp256 ,
142 .Dq ecdsa-sha2-nistp384 ,
143 .Dq ecdsa-sha2-nistp521 ,
149 .Pa /etc/ssh/ssh_known_hosts
151 Print the rsa host key for machine
154 $ ssh-keyscan hostname
157 Find all hosts from the file
159 which have new or different keys from those in the sorted file
160 .Pa ssh_known_hosts :
162 $ ssh-keyscan -t rsa,dsa,ecdsa -f ssh_hosts | \e
163 sort -u - ssh_known_hosts | diff ssh_known_hosts -
170 .An David Mazieres Aq Mt dm@lcs.mit.edu
171 wrote the initial version, and
172 .An Wayne Davison Aq Mt wayned@users.sourceforge.net
173 added support for protocol version 2.
175 It generates "Connection closed by remote host" messages on the consoles
176 of all the machines it scans if the server is older than version 2.9.
177 This is because it opens a connection to the ssh port, reads the public
178 key, and drops the connection as soon as it gets the key.