Annotation of src/usr.bin/ssh/ssh-keyscan.1, Revision 1.38
1.38 ! jmc 1: .\" $OpenBSD: ssh-keyscan.1,v 1.37 2015/11/08 22:30:20 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: .\"
1.38 ! jmc 9: .Dd $Mdocdate: November 8 2015 $
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
1.38 ! jmc 18: .Op Fl 46cHv
1.20 jmc 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.
1.37 djm 57: .It Fl c
58: Request certificates from target hosts instead of plain keys.
1.20 jmc 59: .It Fl f Ar file
60: Read hosts or
1.34 jmc 61: .Dq addrlist namelist
62: pairs from
63: .Ar file ,
64: one per line.
1.20 jmc 65: If
66: .Pa -
67: is supplied instead of a filename,
68: .Nm
69: will read hosts or
1.34 jmc 70: .Dq addrlist namelist
1.20 jmc 71: pairs from the standard input.
1.19 djm 72: .It Fl H
73: Hash all hostnames and addresses in the output.
74: Hashed names may be used normally by
75: .Nm ssh
76: and
77: .Nm sshd ,
78: but they do not reveal identifying information should the file's contents
79: be disclosed.
1.10 markus 80: .It Fl p Ar port
81: Port to connect to on the remote host.
1.11 stevesk 82: .It Fl T Ar timeout
1.15 jmc 83: Set the timeout for connection attempts.
84: If
1.34 jmc 85: .Ar timeout
1.1 markus 86: seconds have elapsed since a connection was initiated to a host or since the
87: last time anything was read from that host, then the connection is
1.15 jmc 88: closed and the host in question considered unavailable.
89: Default is 5 seconds.
1.10 markus 90: .It Fl t Ar type
1.11 stevesk 91: Specifies the type of the key to fetch from the scanned hosts.
1.10 markus 92: The possible values are
93: .Dq rsa1
94: for protocol version 1 and
1.29 djm 95: .Dq dsa ,
1.33 naddy 96: .Dq ecdsa ,
97: .Dq ed25519 ,
1.29 djm 98: or
1.10 markus 99: .Dq rsa
100: for protocol version 2.
101: Multiple values may be specified by separating them with commas.
1.30 djm 102: The default is to fetch
1.35 naddy 103: .Dq rsa ,
104: .Dq ecdsa ,
1.30 djm 105: and
1.35 naddy 106: .Dq ed25519
1.30 djm 107: keys.
1.10 markus 108: .It Fl v
109: Verbose mode.
110: Causes
111: .Nm
112: to print debugging messages about its progress.
1.2 itojun 113: .El
1.9 mpech 114: .Sh SECURITY
1.22 ray 115: If an ssh_known_hosts file is constructed using
1.9 mpech 116: .Nm
1.12 deraadt 117: without verifying the keys, users will be vulnerable to
1.18 brad 118: .Em man in the middle
1.9 mpech 119: attacks.
1.12 deraadt 120: On the other hand, if the security model allows such a risk,
1.9 mpech 121: .Nm
1.12 deraadt 122: can help in the detection of tampered keyfiles or man in the middle
123: attacks which have begun after the ssh_known_hosts file was created.
1.1 markus 124: .Sh FILES
1.34 jmc 125: Input format:
1.10 markus 126: .Bd -literal
1.1 markus 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
1.10 markus 128: .Ed
1.1 markus 129: .Pp
1.35 naddy 130: Output format for RSA1 keys:
1.10 markus 131: .Bd -literal
1.1 markus 132: host-or-namelist bits exponent modulus
1.10 markus 133: .Ed
134: .Pp
1.36 sobrado 135: Output format for RSA, DSA, ECDSA, and Ed25519 keys:
1.10 markus 136: .Bd -literal
137: host-or-namelist keytype base64-encoded-key
138: .Ed
139: .Pp
140: Where
1.34 jmc 141: .Ar keytype
1.10 markus 142: is either
1.29 djm 143: .Dq ecdsa-sha2-nistp256 ,
144: .Dq ecdsa-sha2-nistp384 ,
145: .Dq ecdsa-sha2-nistp521 ,
1.32 markus 146: .Dq ssh-ed25519 ,
1.29 djm 147: .Dq ssh-dss
1.10 markus 148: or
1.29 djm 149: .Dq ssh-rsa .
1.1 markus 150: .Pp
1.13 deraadt 151: .Pa /etc/ssh/ssh_known_hosts
1.17 jmc 152: .Sh EXAMPLES
1.34 jmc 153: Print the rsa host key for machine
154: .Ar hostname :
1.17 jmc 155: .Bd -literal
156: $ ssh-keyscan hostname
157: .Ed
158: .Pp
159: Find all hosts from the file
160: .Pa ssh_hosts
161: which have new or different keys from those in the sorted file
162: .Pa ssh_known_hosts :
163: .Bd -literal
1.35 naddy 164: $ ssh-keyscan -t rsa,dsa,ecdsa,ed25519 -f ssh_hosts | \e
1.17 jmc 165: sort -u - ssh_known_hosts | diff ssh_known_hosts -
166: .Ed
1.1 markus 167: .Sh SEE ALSO
1.4 deraadt 168: .Xr ssh 1 ,
1.1 markus 169: .Xr sshd 8
1.7 mpech 170: .Sh AUTHORS
1.21 jaredy 171: .An -nosplit
1.31 schwarze 172: .An David Mazieres Aq Mt dm@lcs.mit.edu
1.10 markus 173: wrote the initial version, and
1.31 schwarze 174: .An Wayne Davison Aq Mt wayned@users.sourceforge.net
1.10 markus 175: added support for protocol version 2.
1.17 jmc 176: .Sh BUGS
177: It generates "Connection closed by remote host" messages on the consoles
178: of all the machines it scans if the server is older than version 2.9.
179: This is because it opens a connection to the ssh port, reads the public
180: key, and drops the connection as soon as it gets the key.