Annotation of src/usr.bin/ssh/ssh-keyscan.1, Revision 1.30
1.30 ! djm 1: .\" $OpenBSD: ssh-keyscan.1,v 1.29 2010/08/31 11:54:45 djm 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: .\"
1.30 ! djm 9: .Dd $Mdocdate: August 31 2010 $
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
1.20 jmc 18: .Op Fl 46Hv
19: .Op Fl f Ar file
1.10 markus 20: .Op Fl p Ar port
21: .Op Fl T Ar timeout
22: .Op Fl t Ar type
23: .Op Ar host | addrlist namelist
1.25 sobrado 24: .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
1.20 jmc 49: .It Fl 4
50: Forces
51: .Nm
52: to use IPv4 addresses only.
53: .It Fl 6
54: Forces
55: .Nm
56: to use IPv6 addresses only.
57: .It Fl f Ar file
58: Read hosts or
59: .Pa addrlist namelist
60: pairs from this file, one per line.
61: If
62: .Pa -
63: is supplied instead of a filename,
64: .Nm
65: will read hosts or
66: .Pa addrlist namelist
67: pairs from the standard input.
1.19 djm 68: .It Fl H
69: Hash all hostnames and addresses in the output.
70: Hashed names may be used normally by
71: .Nm ssh
72: and
73: .Nm sshd ,
74: but they do not reveal identifying information should the file's contents
75: be disclosed.
1.10 markus 76: .It Fl p Ar port
77: Port to connect to on the remote host.
1.11 stevesk 78: .It Fl T Ar timeout
1.15 jmc 79: Set the timeout for connection attempts.
80: If
1.1 markus 81: .Pa timeout
82: seconds have elapsed since a connection was initiated to a host or since the
83: last time anything was read from that host, then the connection is
1.15 jmc 84: closed and the host in question considered unavailable.
85: Default is 5 seconds.
1.10 markus 86: .It Fl t Ar type
1.11 stevesk 87: Specifies the type of the key to fetch from the scanned hosts.
1.10 markus 88: The possible values are
89: .Dq rsa1
90: for protocol version 1 and
1.29 djm 91: .Dq dsa ,
92: .Dq ecdsa
93: or
1.10 markus 94: .Dq rsa
95: for protocol version 2.
96: Multiple values may be specified by separating them with commas.
1.30 ! djm 97: The default is to fetch
! 98: .Dq rsa
! 99: and
! 100: .Dq ecdsa
! 101: keys.
1.10 markus 102: .It Fl v
103: Verbose mode.
104: Causes
105: .Nm
106: to print debugging messages about its progress.
1.2 itojun 107: .El
1.9 mpech 108: .Sh SECURITY
1.22 ray 109: If an ssh_known_hosts file is constructed using
1.9 mpech 110: .Nm
1.12 deraadt 111: without verifying the keys, users will be vulnerable to
1.18 brad 112: .Em man in the middle
1.9 mpech 113: attacks.
1.12 deraadt 114: On the other hand, if the security model allows such a risk,
1.9 mpech 115: .Nm
1.12 deraadt 116: can help in the detection of tampered keyfiles or man in the middle
117: attacks which have begun after the ssh_known_hosts file was created.
1.1 markus 118: .Sh FILES
119: .Pa Input format:
1.10 markus 120: .Bd -literal
1.1 markus 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
1.10 markus 122: .Ed
1.1 markus 123: .Pp
1.10 markus 124: .Pa Output format for rsa1 keys:
125: .Bd -literal
1.1 markus 126: host-or-namelist bits exponent modulus
1.10 markus 127: .Ed
128: .Pp
1.29 djm 129: .Pa Output format for rsa, dsa and ecdsa keys:
1.10 markus 130: .Bd -literal
131: host-or-namelist keytype base64-encoded-key
132: .Ed
133: .Pp
134: Where
135: .Pa keytype
136: is either
1.29 djm 137: .Dq ecdsa-sha2-nistp256 ,
138: .Dq ecdsa-sha2-nistp384 ,
139: .Dq ecdsa-sha2-nistp521 ,
140: .Dq ssh-dss
1.10 markus 141: or
1.29 djm 142: .Dq ssh-rsa .
1.1 markus 143: .Pp
1.13 deraadt 144: .Pa /etc/ssh/ssh_known_hosts
1.17 jmc 145: .Sh EXAMPLES
146: Print the
1.26 stevesk 147: .Pa rsa
1.17 jmc 148: host key for machine
149: .Pa hostname :
150: .Bd -literal
151: $ ssh-keyscan hostname
152: .Ed
153: .Pp
154: Find all hosts from the file
155: .Pa ssh_hosts
156: which have new or different keys from those in the sorted file
157: .Pa ssh_known_hosts :
158: .Bd -literal
1.29 djm 159: $ ssh-keyscan -t rsa,dsa,ecdsa -f ssh_hosts | \e
1.17 jmc 160: sort -u - ssh_known_hosts | diff ssh_known_hosts -
161: .Ed
1.1 markus 162: .Sh SEE ALSO
1.4 deraadt 163: .Xr ssh 1 ,
1.1 markus 164: .Xr sshd 8
1.7 mpech 165: .Sh AUTHORS
1.21 jaredy 166: .An -nosplit
1.17 jmc 167: .An David Mazieres Aq dm@lcs.mit.edu
1.10 markus 168: wrote the initial version, and
1.17 jmc 169: .An Wayne Davison Aq wayned@users.sourceforge.net
1.10 markus 170: added support for protocol version 2.
1.17 jmc 171: .Sh BUGS
172: It generates "Connection closed by remote host" messages on the consoles
173: of all the machines it scans if the server is older than version 2.9.
174: This is because it opens a connection to the ssh port, reads the public
175: key, and drops the connection as soon as it gets the key.
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