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e9a17296 | 1 | .\" $OpenBSD: ssh-keyscan.1,v 1.14 2002/02/13 08:33:47 mpech Exp $ |
3c0ef626 | 2 | .\" |
3 | .\" Copyright 1995, 1996 by David Mazieres <dm@lcs.mit.edu>. | |
4 | .\" | |
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. | |
8 | .\" | |
9 | .Dd January 1, 1996 | |
10 | .Dt SSH-KEYSCAN 1 | |
11 | .Os | |
12 | .Sh NAME | |
13 | .Nm ssh-keyscan | |
14 | .Nd gather ssh public keys | |
15 | .Sh SYNOPSIS | |
16 | .Nm ssh-keyscan | |
17 | .Op Fl v46 | |
18 | .Op Fl p Ar port | |
19 | .Op Fl T Ar timeout | |
20 | .Op Fl t Ar type | |
21 | .Op Fl f Ar file | |
22 | .Op Ar host | addrlist namelist | |
23 | .Op Ar ... | |
24 | .Sh DESCRIPTION | |
25 | .Nm | |
26 | is a utility for gathering the public ssh host keys of a number of | |
27 | hosts. It was designed to aid in building and verifying | |
28 | .Pa ssh_known_hosts | |
29 | files. | |
30 | .Nm | |
31 | provides a minimal interface suitable for use by shell and perl | |
32 | scripts. | |
33 | .Pp | |
34 | .Nm | |
35 | uses non-blocking socket I/O to contact as many hosts as possible in | |
36 | parallel, so it is very efficient. The keys from a domain of 1,000 | |
37 | hosts can be collected in tens of seconds, even when some of those | |
38 | hosts are down or do not run ssh. For scanning, one does not need | |
39 | login access to the machines that are being scanned, nor does the | |
40 | scanning process involve any encryption. | |
41 | .Pp | |
42 | The options are as follows: | |
43 | .Bl -tag -width Ds | |
44 | .It Fl p Ar port | |
45 | Port to connect to on the remote host. | |
46 | .It Fl T Ar timeout | |
47 | Set the timeout for connection attempts. If | |
48 | .Pa timeout | |
49 | seconds have elapsed since a connection was initiated to a host or since the | |
50 | last time anything was read from that host, then the connection is | |
51 | closed and the host in question considered unavailable. Default is 5 | |
52 | seconds. | |
53 | .It Fl t Ar type | |
54 | Specifies the type of the key to fetch from the scanned hosts. | |
55 | The possible values are | |
56 | .Dq rsa1 | |
57 | for protocol version 1 and | |
58 | .Dq rsa | |
59 | or | |
60 | .Dq dsa | |
61 | for protocol version 2. | |
62 | Multiple values may be specified by separating them with commas. | |
63 | The default is | |
64 | .Dq rsa1 . | |
65 | .It Fl f Ar filename | |
66 | Read hosts or | |
67 | .Pa addrlist namelist | |
68 | pairs from this file, one per line. | |
69 | If | |
70 | .Pa - | |
71 | is supplied instead of a filename, | |
72 | .Nm | |
73 | will read hosts or | |
74 | .Pa addrlist namelist | |
75 | pairs from the standard input. | |
76 | .It Fl v | |
77 | Verbose mode. | |
78 | Causes | |
79 | .Nm | |
80 | to print debugging messages about its progress. | |
81 | .It Fl 4 | |
82 | Forces | |
83 | .Nm | |
84 | to use IPv4 addresses only. | |
85 | .It Fl 6 | |
86 | Forces | |
87 | .Nm | |
88 | to use IPv6 addresses only. | |
89 | .El | |
90 | .Sh SECURITY | |
91 | If a ssh_known_hosts file is constructed using | |
92 | .Nm | |
93 | without verifying the keys, users will be vulnerable to | |
94 | .I man in the middle | |
95 | attacks. | |
96 | On the other hand, if the security model allows such a risk, | |
97 | .Nm | |
98 | can help in the detection of tampered keyfiles or man in the middle | |
99 | attacks which have begun after the ssh_known_hosts file was created. | |
100 | .Sh EXAMPLES | |
101 | .Pp | |
102 | Print the | |
103 | .Pa rsa1 | |
104 | host key for machine | |
105 | .Pa hostname : | |
106 | .Bd -literal | |
e9a17296 | 107 | $ ssh-keyscan hostname |
3c0ef626 | 108 | .Ed |
109 | .Pp | |
110 | Find all hosts from the file | |
111 | .Pa ssh_hosts | |
112 | which have new or different keys from those in the sorted file | |
113 | .Pa ssh_known_hosts : | |
114 | .Bd -literal | |
e9a17296 | 115 | $ ssh-keyscan -t rsa,dsa -f ssh_hosts | \e\ |
3c0ef626 | 116 | sort -u - ssh_known_hosts | diff ssh_known_hosts - |
117 | .Ed | |
118 | .Sh FILES | |
119 | .Pa Input format: | |
120 | .Bd -literal | |
121 | 1.2.3.4,1.2.4.4 name.my.domain,name,n.my.domain,n,1.2.3.4,1.2.4.4 | |
122 | .Ed | |
123 | .Pp | |
124 | .Pa Output format for rsa1 keys: | |
125 | .Bd -literal | |
126 | host-or-namelist bits exponent modulus | |
127 | .Ed | |
128 | .Pp | |
129 | .Pa Output format for rsa and dsa keys: | |
130 | .Bd -literal | |
131 | host-or-namelist keytype base64-encoded-key | |
132 | .Ed | |
133 | .Pp | |
134 | Where | |
135 | .Pa keytype | |
136 | is either | |
137 | .Dq ssh-rsa | |
138 | or | |
139 | .Dq ssh-dsa . | |
140 | .Pp | |
e9a17296 | 141 | .Pa /etc/ssh/ssh_known_hosts |
3c0ef626 | 142 | .Sh BUGS |
143 | It generates "Connection closed by remote host" messages on the consoles | |
144 | of all the machines it scans if the server is older than version 2.9. | |
145 | This is because it opens a connection to the ssh port, reads the public | |
146 | key, and drops the connection as soon as it gets the key. | |
147 | .Sh SEE ALSO | |
148 | .Xr ssh 1 , | |
149 | .Xr sshd 8 | |
150 | .Sh AUTHORS | |
151 | David Mazieres <dm@lcs.mit.edu> | |
152 | wrote the initial version, and | |
153 | Wayne Davison <wayned@users.sourceforge.net> | |
154 | added support for protocol version 2. |