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1 | SSH-KEYSCAN(1) OpenBSD Reference Manual SSH-KEYSCAN(1) | ||
2 | |||
3 | NAME | ||
4 | ssh-keyscan - gather ssh public keys | ||
5 | |||
6 | SYNOPSIS | ||
7 | ssh-keyscan [-46Hv] [-f file] [-p port] [-T timeout] [-t type] | ||
8 | [host | addrlist namelist] ... | ||
9 | |||
10 | DESCRIPTION | ||
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 | ``rsa'' or ``dsa'' for protocol version 2. Multiple values may | ||
52 | be specified by separating them with commas. The default is | ||
53 | ``rsa''. | ||
54 | |||
55 | -v Verbose mode. Causes ssh-keyscan to print debugging messages | ||
56 | about its progress. | ||
57 | |||
58 | SECURITY | ||
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 | |||
66 | FILES | ||
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 and dsa keys: | ||
76 | |||
77 | host-or-namelist keytype base64-encoded-key | ||
78 | |||
79 | Where keytype is either ``ssh-rsa'' or ``ssh-dss''. | ||
80 | |||
81 | /etc/ssh/ssh_known_hosts | ||
82 | |||
83 | EXAMPLES | ||
84 | Print the rsa host key for machine hostname: | ||
85 | |||
86 | $ ssh-keyscan hostname | ||
87 | |||
88 | Find all hosts from the file ssh_hosts which have new or different keys | ||
89 | from those in the sorted file ssh_known_hosts: | ||
90 | |||
91 | $ ssh-keyscan -t rsa,dsa -f ssh_hosts | \ | ||
92 | sort -u - ssh_known_hosts | diff ssh_known_hosts - | ||
93 | |||
94 | SEE ALSO | ||
95 | ssh(1), sshd(8) | ||
96 | |||
97 | AUTHORS | ||
98 | David Mazieres <dm@lcs.mit.edu> wrote the initial version, and Wayne | ||
99 | Davison <wayned@users.sourceforge.net> added support for protocol version | ||
100 | 2. | ||
101 | |||
102 | BUGS | ||
103 | It generates "Connection closed by remote host" messages on the consoles | ||
104 | of all the machines it scans if the server is older than version 2.9. | ||
105 | This is because it opens a connection to the ssh port, reads the public | ||
106 | key, and drops the connection as soon as it gets the key. | ||
107 | |||
108 | OpenBSD 4.8 January 9, 2010 OpenBSD 4.8 | ||