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1SSH-KEYSCAN(1) OpenBSD Reference Manual SSH-KEYSCAN(1)
2
3NAME
4 ssh-keyscan - gather ssh public keys
5
6SYNOPSIS
7 ssh-keyscan [-46Hv] [-f file] [-p port] [-T timeout] [-t type]
8 [host | addrlist namelist] ...
9
10DESCRIPTION
11 ssh-keyscan is a utility for gathering the public ssh host keys of a
12 number of hosts. It was designed to aid in building and verifying
13 ssh_known_hosts files. ssh-keyscan provides a minimal interface suitable
14 for use by shell and perl scripts.
15
16 ssh-keyscan uses non-blocking socket I/O to contact as many hosts as
17 possible in parallel, so it is very efficient. The keys from a domain of
18 1,000 hosts can be collected in tens of seconds, even when some of those
19 hosts are down or do not run ssh. For scanning, one does not need login
20 access to the machines that are being scanned, nor does the scanning
21 process involve any encryption.
22
23 The options are as follows:
24
25 -4 Forces ssh-keyscan to use IPv4 addresses only.
26
27 -6 Forces ssh-keyscan to use IPv6 addresses only.
28
29 -f file
30 Read hosts or addrlist namelist pairs from this file, one per
31 line. If - is supplied instead of a filename, ssh-keyscan will
32 read hosts or addrlist namelist pairs from the standard input.
33
34 -H Hash all hostnames and addresses in the output. Hashed names may
35 be used normally by ssh and sshd, but they do not reveal
36 identifying information should the file's contents be disclosed.
37
38 -p port
39 Port to connect to on the remote host.
40
41 -T timeout
42 Set the timeout for connection attempts. If timeout seconds have
43 elapsed since a connection was initiated to a host or since the
44 last time anything was read from that host, then the connection
45 is closed and the host in question considered unavailable.
46 Default is 5 seconds.
47
48 -t type
49 Specifies the type of the key to fetch from the scanned hosts.
50 The possible values are ``rsa1'' for protocol version 1 and
51 ``dsa'', ``ecdsa'' or ``rsa'' for protocol version 2. Multiple
52 values may be specified by separating them with commas. The
53 default is ``rsa''.
54
55 -v Verbose mode. Causes ssh-keyscan to print debugging messages
56 about its progress.
57
58SECURITY
59 If an ssh_known_hosts file is constructed using ssh-keyscan without
60 verifying the keys, users will be vulnerable to man in the middle
61 attacks. On the other hand, if the security model allows such a risk,
62 ssh-keyscan can help in the detection of tampered keyfiles or man in the
63 middle attacks which have begun after the ssh_known_hosts file was
64 created.
65
66FILES
67 Input format:
68
69 1.2.3.4,1.2.4.4 name.my.domain,name,n.my.domain,n,1.2.3.4,1.2.4.4
70
71 Output format for rsa1 keys:
72
73 host-or-namelist bits exponent modulus
74
75 Output format for rsa, dsa and ecdsa keys:
76
77 host-or-namelist keytype base64-encoded-key
78
79 Where keytype is either ``ecdsa-sha2-nistp256'', ``ecdsa-sha2-nistp384'',
80 ``ecdsa-sha2-nistp521'', ``ssh-dss'' or ``ssh-rsa''.
81
82 /etc/ssh/ssh_known_hosts
83
84EXAMPLES
85 Print the rsa host key for machine hostname:
86
87 $ ssh-keyscan hostname
88
89 Find all hosts from the file ssh_hosts which have new or different keys
90 from those in the sorted file ssh_known_hosts:
91
92 $ ssh-keyscan -t rsa,dsa,ecdsa -f ssh_hosts | \
93 sort -u - ssh_known_hosts | diff ssh_known_hosts -
94
95SEE ALSO
96 ssh(1), sshd(8)
97
98AUTHORS
99 David Mazieres <dm@lcs.mit.edu> wrote the initial version, and Wayne
100 Davison <wayned@users.sourceforge.net> added support for protocol version
101 2.
102
103BUGS
104 It generates "Connection closed by remote host" messages on the consoles
105 of all the machines it scans if the server is older than version 2.9.
106 This is because it opens a connection to the ssh port, reads the public
107 key, and drops the connection as soon as it gets the key.
108
109OpenBSD 5.0 August 31, 2010 OpenBSD 5.0