1 .\" $OpenBSD: ssh-keyscan.1,v 1.38 2015/11/08 23:24:03 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.
9 .Dd $Mdocdate: November 8 2015 $
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:
52 to use IPv4 addresses only.
56 to use IPv6 addresses only.
58 Request certificates from target hosts instead of plain keys.
67 is supplied instead of a filename,
71 pairs from the standard input.
73 Hash all hostnames and addresses in the output.
74 Hashed names may be used normally by
78 but they do not reveal identifying information should the file's contents
81 Port to connect to on the remote host.
83 Set the timeout for connection attempts.
86 seconds have elapsed since a connection was initiated to a host or since the
87 last time anything was read from that host, then the connection is
88 closed and the host in question considered unavailable.
91 Specifies the type of the key to fetch from the scanned hosts.
92 The possible values are
94 for protocol version 1 and
100 for protocol version 2.
101 Multiple values may be specified by separating them with commas.
102 The default is to fetch
112 to print debugging messages about its progress.
115 If an ssh_known_hosts file is constructed using
117 without verifying the keys, users will be vulnerable to
118 .Em man in the middle
120 On the other hand, if the security model allows such a risk,
122 can help in the detection of tampered keyfiles or man in the middle
123 attacks which have begun after the ssh_known_hosts file was created.
127 1.2.3.4,1.2.4.4 name.my.domain,name,n.my.domain,n,1.2.3.4,1.2.4.4
130 Output format for RSA1 keys:
132 host-or-namelist bits exponent modulus
135 Output format for RSA, DSA, ECDSA, and Ed25519 keys:
137 host-or-namelist keytype base64-encoded-key
143 .Dq ecdsa-sha2-nistp256 ,
144 .Dq ecdsa-sha2-nistp384 ,
145 .Dq ecdsa-sha2-nistp521 ,
151 .Pa /etc/ssh/ssh_known_hosts
153 Print the rsa host key for machine
156 $ ssh-keyscan hostname
159 Find all hosts from the file
161 which have new or different keys from those in the sorted file
162 .Pa ssh_known_hosts :
164 $ ssh-keyscan -t rsa,dsa,ecdsa,ed25519 -f ssh_hosts | \e
165 sort -u - ssh_known_hosts | diff ssh_known_hosts -
172 .An David Mazieres Aq Mt dm@lcs.mit.edu
173 wrote the initial version, and
174 .An Wayne Davison Aq Mt wayned@users.sourceforge.net
175 added support for protocol version 2.
177 It generates "Connection closed by remote host" messages on the consoles
178 of all the machines it scans if the server is older than version 2.9.
179 This is because it opens a connection to the ssh port, reads the public
180 key, and drops the connection as soon as it gets the key.