1.\" $OpenBSD: ssh-keyscan.1,v 1.17 2003/06/10 09:12:11 jmc Exp $
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.Bk -words
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 ...
25.Ek
26.Sh DESCRIPTION
27.Nm
28is a utility for gathering the public ssh host keys of a number of
29hosts.
30It was designed to aid in building and verifying
31.Pa ssh_known_hosts
32files.
33.Nm
34provides a minimal interface suitable for use by shell and perl
35scripts.
36.Pp
37.Nm
38uses non-blocking socket I/O to contact as many hosts as possible in
39parallel, so it is very efficient.
40The keys from a domain of 1,000
41hosts can be collected in tens of seconds, even when some of those
42hosts are down or do not run ssh.
43For scanning, one does not need
44login access to the machines that are being scanned, nor does the
45scanning process involve any encryption.
46.Pp
47The options are as follows:
48.Bl -tag -width Ds
49.It Fl p Ar port
50Port to connect to on the remote host.
51.It Fl T Ar timeout
52Set the timeout for connection attempts.
53If
54.Pa timeout
55seconds have elapsed since a connection was initiated to a host or since the
56last time anything was read from that host, then the connection is
57closed and the host in question considered unavailable.
58Default is 5 seconds.
59.It Fl t Ar type
60Specifies the type of the key to fetch from the scanned hosts.
61The possible values are
62.Dq rsa1
63for protocol version 1 and
64.Dq rsa
65or
66.Dq dsa
67for protocol version 2.
68Multiple values may be specified by separating them with commas.
69The default is
70.Dq rsa1 .
71.It Fl f Ar filename
72Read hosts or
73.Pa addrlist namelist
74pairs from this file, one per line.
75If
76.Pa -
77is supplied instead of a filename,
78.Nm
79will read hosts or
80.Pa addrlist namelist
81pairs from the standard input.
82.It Fl v
83Verbose mode.
84Causes
85.Nm
86to print debugging messages about its progress.
87.It Fl 4
88Forces
89.Nm
90to use IPv4 addresses only.
91.It Fl 6
92Forces
93.Nm
94to use IPv6 addresses only.
95.El
96.Sh SECURITY
97If a ssh_known_hosts file is constructed using
98.Nm
99without verifying the keys, users will be vulnerable to
100.I man in the middle
101attacks.
102On the other hand, if the security model allows such a risk,
103.Nm
104can help in the detection of tampered keyfiles or man in the middle
105attacks which have begun after the ssh_known_hosts file was created.
106.Sh FILES
107.Pa Input format:
108.Bd -literal
1091.2.3.4,1.2.4.4 name.my.domain,name,n.my.domain,n,1.2.3.4,1.2.4.4
110.Ed
111.Pp
112.Pa Output format for rsa1 keys:
113.Bd -literal
114host-or-namelist bits exponent modulus
115.Ed
116.Pp
117.Pa Output format for rsa and dsa keys:
118.Bd -literal
119host-or-namelist keytype base64-encoded-key
120.Ed
121.Pp
122Where
123.Pa keytype
124is either
125.Dq ssh-rsa
126or
127.Dq ssh-dss .
128.Pp
129.Pa /etc/ssh/ssh_known_hosts
130.Sh EXAMPLES
131Print the
132.Pa rsa1
133host key for machine
134.Pa hostname :
135.Bd -literal
136$ ssh-keyscan hostname
137.Ed
138.Pp
139Find all hosts from the file
140.Pa ssh_hosts
141which have new or different keys from those in the sorted file
142.Pa ssh_known_hosts :
143.Bd -literal
144$ ssh-keyscan -t rsa,dsa -f ssh_hosts | \e
145 sort -u - ssh_known_hosts | diff ssh_known_hosts -
146.Ed
147.Sh SEE ALSO
148.Xr ssh 1 ,
149.Xr sshd 8
150.Sh AUTHORS
151.An David Mazieres Aq dm@lcs.mit.edu
152wrote the initial version, and
153.An Wayne Davison Aq wayned@users.sourceforge.net
154added support for protocol version 2.
155.Sh BUGS
156It generates "Connection closed by remote host" messages on the consoles
157of all the machines it scans if the server is older than version 2.9.
158This is because it opens a connection to the ssh port, reads the public
159key, and drops the connection as soon as it gets the key.
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.Bk -words
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 ...
25.Ek
26.Sh DESCRIPTION
27.Nm
28is a utility for gathering the public ssh host keys of a number of
29hosts.
30It was designed to aid in building and verifying
31.Pa ssh_known_hosts
32files.
33.Nm
34provides a minimal interface suitable for use by shell and perl
35scripts.
36.Pp
37.Nm
38uses non-blocking socket I/O to contact as many hosts as possible in
39parallel, so it is very efficient.
40The keys from a domain of 1,000
41hosts can be collected in tens of seconds, even when some of those
42hosts are down or do not run ssh.
43For scanning, one does not need
44login access to the machines that are being scanned, nor does the
45scanning process involve any encryption.
46.Pp
47The options are as follows:
48.Bl -tag -width Ds
49.It Fl p Ar port
50Port to connect to on the remote host.
51.It Fl T Ar timeout
52Set the timeout for connection attempts.
53If
54.Pa timeout
55seconds have elapsed since a connection was initiated to a host or since the
56last time anything was read from that host, then the connection is
57closed and the host in question considered unavailable.
58Default is 5 seconds.
59.It Fl t Ar type
60Specifies the type of the key to fetch from the scanned hosts.
61The possible values are
62.Dq rsa1
63for protocol version 1 and
64.Dq rsa
65or
66.Dq dsa
67for protocol version 2.
68Multiple values may be specified by separating them with commas.
69The default is
70.Dq rsa1 .
71.It Fl f Ar filename
72Read hosts or
73.Pa addrlist namelist
74pairs from this file, one per line.
75If
76.Pa -
77is supplied instead of a filename,
78.Nm
79will read hosts or
80.Pa addrlist namelist
81pairs from the standard input.
82.It Fl v
83Verbose mode.
84Causes
85.Nm
86to print debugging messages about its progress.
87.It Fl 4
88Forces
89.Nm
90to use IPv4 addresses only.
91.It Fl 6
92Forces
93.Nm
94to use IPv6 addresses only.
95.El
96.Sh SECURITY
97If a ssh_known_hosts file is constructed using
98.Nm
99without verifying the keys, users will be vulnerable to
100.I man in the middle
101attacks.
102On the other hand, if the security model allows such a risk,
103.Nm
104can help in the detection of tampered keyfiles or man in the middle
105attacks which have begun after the ssh_known_hosts file was created.
106.Sh FILES
107.Pa Input format:
108.Bd -literal
1091.2.3.4,1.2.4.4 name.my.domain,name,n.my.domain,n,1.2.3.4,1.2.4.4
110.Ed
111.Pp
112.Pa Output format for rsa1 keys:
113.Bd -literal
114host-or-namelist bits exponent modulus
115.Ed
116.Pp
117.Pa Output format for rsa and dsa keys:
118.Bd -literal
119host-or-namelist keytype base64-encoded-key
120.Ed
121.Pp
122Where
123.Pa keytype
124is either
125.Dq ssh-rsa
126or
127.Dq ssh-dss .
128.Pp
129.Pa /etc/ssh/ssh_known_hosts
130.Sh EXAMPLES
131Print the
132.Pa rsa1
133host key for machine
134.Pa hostname :
135.Bd -literal
136$ ssh-keyscan hostname
137.Ed
138.Pp
139Find all hosts from the file
140.Pa ssh_hosts
141which have new or different keys from those in the sorted file
142.Pa ssh_known_hosts :
143.Bd -literal
144$ ssh-keyscan -t rsa,dsa -f ssh_hosts | \e
145 sort -u - ssh_known_hosts | diff ssh_known_hosts -
146.Ed
147.Sh SEE ALSO
148.Xr ssh 1 ,
149.Xr sshd 8
150.Sh AUTHORS
151.An David Mazieres Aq dm@lcs.mit.edu
152wrote the initial version, and
153.An Wayne Davison Aq wayned@users.sourceforge.net
154added support for protocol version 2.
155.Sh BUGS
156It generates "Connection closed by remote host" messages on the consoles
157of all the machines it scans if the server is older than version 2.9.
158This is because it opens a connection to the ssh port, reads the public
159key, and drops the connection as soon as it gets the key.