Annotation of src/usr.bin/ssh/ssh-keyscan.1, Revision 1.19
1.19 ! djm 1: .\" $OpenBSD: ssh-keyscan.1,v 1.18 2004/07/12 23:34:25 brad Exp $
1.4 deraadt 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
1.6 pvalchev 7: .\" OpenBSD project by leaving this copyright notice intact.
1.3 niklas 8: .\"
1.1 markus 9: .Dd January 1, 1996
1.4 deraadt 10: .Dt SSH-KEYSCAN 1
1.1 markus 11: .Os
12: .Sh NAME
13: .Nm ssh-keyscan
14: .Nd gather ssh public keys
15: .Sh SYNOPSIS
16: .Nm ssh-keyscan
1.15 jmc 17: .Bk -words
1.19 ! djm 18: .Op Fl Hv46
1.10 markus 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 ...
1.15 jmc 25: .Ek
1.1 markus 26: .Sh DESCRIPTION
27: .Nm
28: is a utility for gathering the public ssh host keys of a number of
1.15 jmc 29: hosts.
30: It was designed to aid in building and verifying
1.1 markus 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
1.15 jmc 39: parallel, so it is very efficient.
40: The keys from a domain of 1,000
1.1 markus 41: hosts can be collected in tens of seconds, even when some of those
1.15 jmc 42: hosts are down or do not run ssh.
43: For scanning, one does not need
1.12 deraadt 44: login access to the machines that are being scanned, nor does the
45: scanning process involve any encryption.
1.9 mpech 46: .Pp
47: The options are as follows:
1.1 markus 48: .Bl -tag -width Ds
1.19 ! djm 49: .It Fl H
! 50: Hash all hostnames and addresses in the output.
! 51: Hashed names may be used normally by
! 52: .Nm ssh
! 53: and
! 54: .Nm sshd ,
! 55: but they do not reveal identifying information should the file's contents
! 56: be disclosed.
1.10 markus 57: .It Fl p Ar port
58: Port to connect to on the remote host.
1.11 stevesk 59: .It Fl T Ar timeout
1.15 jmc 60: Set the timeout for connection attempts.
61: If
1.1 markus 62: .Pa timeout
63: seconds have elapsed since a connection was initiated to a host or since the
64: last time anything was read from that host, then the connection is
1.15 jmc 65: closed and the host in question considered unavailable.
66: Default is 5 seconds.
1.10 markus 67: .It Fl t Ar type
1.11 stevesk 68: Specifies the type of the key to fetch from the scanned hosts.
1.10 markus 69: The possible values are
70: .Dq rsa1
71: for protocol version 1 and
72: .Dq rsa
73: or
74: .Dq dsa
75: for protocol version 2.
76: Multiple values may be specified by separating them with commas.
77: The default is
78: .Dq rsa1 .
79: .It Fl f Ar filename
1.8 itojun 80: Read hosts or
1.1 markus 81: .Pa addrlist namelist
82: pairs from this file, one per line.
83: If
84: .Pa -
85: is supplied instead of a filename,
86: .Nm
1.8 itojun 87: will read hosts or
1.1 markus 88: .Pa addrlist namelist
89: pairs from the standard input.
1.10 markus 90: .It Fl v
91: Verbose mode.
92: Causes
93: .Nm
94: to print debugging messages about its progress.
95: .It Fl 4
96: Forces
97: .Nm
98: to use IPv4 addresses only.
99: .It Fl 6
100: Forces
101: .Nm
102: to use IPv6 addresses only.
1.2 itojun 103: .El
1.9 mpech 104: .Sh SECURITY
1.12 deraadt 105: If a ssh_known_hosts file is constructed using
1.9 mpech 106: .Nm
1.12 deraadt 107: without verifying the keys, users will be vulnerable to
1.18 brad 108: .Em man in the middle
1.9 mpech 109: attacks.
1.12 deraadt 110: On the other hand, if the security model allows such a risk,
1.9 mpech 111: .Nm
1.12 deraadt 112: can help in the detection of tampered keyfiles or man in the middle
113: attacks which have begun after the ssh_known_hosts file was created.
1.1 markus 114: .Sh FILES
115: .Pa Input format:
1.10 markus 116: .Bd -literal
1.1 markus 117: 1.2.3.4,1.2.4.4 name.my.domain,name,n.my.domain,n,1.2.3.4,1.2.4.4
1.10 markus 118: .Ed
1.1 markus 119: .Pp
1.10 markus 120: .Pa Output format for rsa1 keys:
121: .Bd -literal
1.1 markus 122: host-or-namelist bits exponent modulus
1.10 markus 123: .Ed
124: .Pp
125: .Pa Output format for rsa and dsa keys:
126: .Bd -literal
127: host-or-namelist keytype base64-encoded-key
128: .Ed
129: .Pp
130: Where
131: .Pa keytype
132: is either
133: .Dq ssh-rsa
134: or
1.16 markus 135: .Dq ssh-dss .
1.1 markus 136: .Pp
1.13 deraadt 137: .Pa /etc/ssh/ssh_known_hosts
1.17 jmc 138: .Sh EXAMPLES
139: Print the
140: .Pa rsa1
141: host key for machine
142: .Pa hostname :
143: .Bd -literal
144: $ ssh-keyscan hostname
145: .Ed
146: .Pp
147: Find all hosts from the file
148: .Pa ssh_hosts
149: which have new or different keys from those in the sorted file
150: .Pa ssh_known_hosts :
151: .Bd -literal
152: $ ssh-keyscan -t rsa,dsa -f ssh_hosts | \e
153: sort -u - ssh_known_hosts | diff ssh_known_hosts -
154: .Ed
1.1 markus 155: .Sh SEE ALSO
1.4 deraadt 156: .Xr ssh 1 ,
1.1 markus 157: .Xr sshd 8
1.7 mpech 158: .Sh AUTHORS
1.17 jmc 159: .An David Mazieres Aq dm@lcs.mit.edu
1.10 markus 160: wrote the initial version, and
1.17 jmc 161: .An Wayne Davison Aq wayned@users.sourceforge.net
1.10 markus 162: added support for protocol version 2.
1.17 jmc 163: .Sh BUGS
164: It generates "Connection closed by remote host" messages on the consoles
165: of all the machines it scans if the server is older than version 2.9.
166: This is because it opens a connection to the ssh port, reads the public
167: key, and drops the connection as soon as it gets the key.
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