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a4e5acef | 1 | .\" $OpenBSD: ssh-keyscan.1,v 1.15 2003/03/28 10:11:43 jmc Exp $ |
4371658c | 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 | |
aa144206 | 7 | .\" OpenBSD project by leaving this copyright notice intact. |
23c2a7a5 | 8 | .\" |
f6fdbddf | 9 | .Dd January 1, 1996 |
4371658c | 10 | .Dt SSH-KEYSCAN 1 |
f6fdbddf | 11 | .Os |
12 | .Sh NAME | |
13 | .Nm ssh-keyscan | |
14 | .Nd gather ssh public keys | |
15 | .Sh SYNOPSIS | |
16 | .Nm ssh-keyscan | |
a4e5acef | 17 | .Bk -words |
5061072f | 18 | .Op Fl v46 |
19 | .Op Fl p Ar port | |
20 | .Op Fl T Ar timeout | |
21 | .Op Fl t Ar type | |
22 | .Op Fl f Ar file | |
23 | .Op Ar host | addrlist namelist | |
24 | .Op Ar ... | |
a4e5acef | 25 | .Ek |
f6fdbddf | 26 | .Sh DESCRIPTION |
27 | .Nm | |
28 | is a utility for gathering the public ssh host keys of a number of | |
a4e5acef | 29 | hosts. |
30 | It was designed to aid in building and verifying | |
f6fdbddf | 31 | .Pa ssh_known_hosts |
32 | files. | |
33 | .Nm | |
34 | provides a minimal interface suitable for use by shell and perl | |
35 | scripts. | |
36 | .Pp | |
37 | .Nm | |
38 | uses non-blocking socket I/O to contact as many hosts as possible in | |
a4e5acef | 39 | parallel, so it is very efficient. |
40 | The keys from a domain of 1,000 | |
f6fdbddf | 41 | hosts can be collected in tens of seconds, even when some of those |
a4e5acef | 42 | hosts are down or do not run ssh. |
43 | For scanning, one does not need | |
91789042 | 44 | login access to the machines that are being scanned, nor does the |
45 | scanning process involve any encryption. | |
0f6d5acf | 46 | .Pp |
47 | The options are as follows: | |
f6fdbddf | 48 | .Bl -tag -width Ds |
5061072f | 49 | .It Fl p Ar port |
50 | Port to connect to on the remote host. | |
75304f85 | 51 | .It Fl T Ar timeout |
a4e5acef | 52 | Set the timeout for connection attempts. |
53 | If | |
f6fdbddf | 54 | .Pa timeout |
55 | seconds have elapsed since a connection was initiated to a host or since the | |
56 | last time anything was read from that host, then the connection is | |
a4e5acef | 57 | closed and the host in question considered unavailable. |
58 | Default is 5 seconds. | |
5061072f | 59 | .It Fl t Ar type |
75304f85 | 60 | Specifies the type of the key to fetch from the scanned hosts. |
5061072f | 61 | The possible values are |
62 | .Dq rsa1 | |
63 | for protocol version 1 and | |
64 | .Dq rsa | |
65 | or | |
66 | .Dq dsa | |
67 | for protocol version 2. | |
68 | Multiple values may be specified by separating them with commas. | |
69 | The default is | |
70 | .Dq rsa1 . | |
71 | .It Fl f Ar filename | |
3730bb22 | 72 | Read hosts or |
f6fdbddf | 73 | .Pa addrlist namelist |
74 | pairs from this file, one per line. | |
75 | If | |
76 | .Pa - | |
77 | is supplied instead of a filename, | |
78 | .Nm | |
3730bb22 | 79 | will read hosts or |
f6fdbddf | 80 | .Pa addrlist namelist |
81 | pairs from the standard input. | |
5061072f | 82 | .It Fl v |
83 | Verbose mode. | |
84 | Causes | |
85 | .Nm | |
86 | to print debugging messages about its progress. | |
87 | .It Fl 4 | |
88 | Forces | |
89 | .Nm | |
90 | to use IPv4 addresses only. | |
91 | .It Fl 6 | |
92 | Forces | |
93 | .Nm | |
94 | to use IPv6 addresses only. | |
9616313f | 95 | .El |
0f6d5acf | 96 | .Sh SECURITY |
91789042 | 97 | If a ssh_known_hosts file is constructed using |
0f6d5acf | 98 | .Nm |
91789042 | 99 | without verifying the keys, users will be vulnerable to |
0f6d5acf | 100 | .I man in the middle |
101 | attacks. | |
91789042 | 102 | On the other hand, if the security model allows such a risk, |
0f6d5acf | 103 | .Nm |
91789042 | 104 | can help in the detection of tampered keyfiles or man in the middle |
105 | attacks which have begun after the ssh_known_hosts file was created. | |
f6fdbddf | 106 | .Sh EXAMPLES |
5061072f | 107 | .Pp |
108 | Print the | |
109 | .Pa rsa1 | |
110 | host key for machine | |
f6fdbddf | 111 | .Pa hostname : |
112 | .Bd -literal | |
241b0041 | 113 | $ ssh-keyscan hostname |
f6fdbddf | 114 | .Ed |
115 | .Pp | |
116 | Find all hosts from the file | |
117 | .Pa ssh_hosts | |
118 | which have new or different keys from those in the sorted file | |
119 | .Pa ssh_known_hosts : | |
120 | .Bd -literal | |
241b0041 | 121 | $ ssh-keyscan -t rsa,dsa -f ssh_hosts | \e\ |
5061072f | 122 | sort -u - ssh_known_hosts | diff ssh_known_hosts - |
f6fdbddf | 123 | .Ed |
f6fdbddf | 124 | .Sh FILES |
f6fdbddf | 125 | .Pa Input format: |
5061072f | 126 | .Bd -literal |
f6fdbddf | 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 |
5061072f | 128 | .Ed |
f6fdbddf | 129 | .Pp |
5061072f | 130 | .Pa Output format for rsa1 keys: |
131 | .Bd -literal | |
f6fdbddf | 132 | host-or-namelist bits exponent modulus |
5061072f | 133 | .Ed |
134 | .Pp | |
135 | .Pa Output format for rsa and dsa keys: | |
136 | .Bd -literal | |
137 | host-or-namelist keytype base64-encoded-key | |
138 | .Ed | |
139 | .Pp | |
140 | Where | |
141 | .Pa keytype | |
142 | is either | |
143 | .Dq ssh-rsa | |
144 | or | |
145 | .Dq ssh-dsa . | |
f6fdbddf | 146 | .Pp |
2a8a6488 | 147 | .Pa /etc/ssh/ssh_known_hosts |
f6fdbddf | 148 | .Sh BUGS |
149 | It generates "Connection closed by remote host" messages on the consoles | |
5061072f | 150 | of all the machines it scans if the server is older than version 2.9. |
f6fdbddf | 151 | This is because it opens a connection to the ssh port, reads the public |
152 | key, and drops the connection as soon as it gets the key. | |
153 | .Sh SEE ALSO | |
4371658c | 154 | .Xr ssh 1 , |
f6fdbddf | 155 | .Xr sshd 8 |
a5a2da3b | 156 | .Sh AUTHORS |
f6fdbddf | 157 | David Mazieres <dm@lcs.mit.edu> |
5061072f | 158 | wrote the initial version, and |
159 | Wayne Davison <wayned@users.sourceforge.net> | |
160 | added support for protocol version 2. |