Annotation of src/usr.bin/ssh/ssh-keyscan.1, Revision 1.40
1.40 ! jmc 1: .\" $OpenBSD: ssh-keyscan.1,v 1.39 2017/04/30 23:18:44 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: .\"
1.40 ! jmc 9: .Dd $Mdocdate: April 30 2017 $
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
1.29 djm 93: .Dq dsa ,
1.33 naddy 94: .Dq ecdsa ,
95: .Dq ed25519 ,
1.29 djm 96: or
1.40 ! jmc 97: .Dq rsa .
1.10 markus 98: Multiple values may be specified by separating them with commas.
1.30 djm 99: The default is to fetch
1.35 naddy 100: .Dq rsa ,
101: .Dq ecdsa ,
1.30 djm 102: and
1.35 naddy 103: .Dq ed25519
1.30 djm 104: keys.
1.10 markus 105: .It Fl v
106: Verbose mode.
107: Causes
108: .Nm
109: to print debugging messages about its progress.
1.2 itojun 110: .El
1.9 mpech 111: .Sh SECURITY
1.22 ray 112: If an ssh_known_hosts file is constructed using
1.9 mpech 113: .Nm
1.12 deraadt 114: without verifying the keys, users will be vulnerable to
1.18 brad 115: .Em man in the middle
1.9 mpech 116: attacks.
1.12 deraadt 117: On the other hand, if the security model allows such a risk,
1.9 mpech 118: .Nm
1.12 deraadt 119: can help in the detection of tampered keyfiles or man in the middle
120: attacks which have begun after the ssh_known_hosts file was created.
1.1 markus 121: .Sh FILES
1.34 jmc 122: Input format:
1.10 markus 123: .Bd -literal
1.1 markus 124: 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 125: .Ed
126: .Pp
1.36 sobrado 127: Output format for RSA, DSA, ECDSA, and Ed25519 keys:
1.10 markus 128: .Bd -literal
129: host-or-namelist keytype base64-encoded-key
130: .Ed
131: .Pp
132: Where
1.34 jmc 133: .Ar keytype
1.10 markus 134: is either
1.29 djm 135: .Dq ecdsa-sha2-nistp256 ,
136: .Dq ecdsa-sha2-nistp384 ,
137: .Dq ecdsa-sha2-nistp521 ,
1.32 markus 138: .Dq ssh-ed25519 ,
1.29 djm 139: .Dq ssh-dss
1.10 markus 140: or
1.29 djm 141: .Dq ssh-rsa .
1.1 markus 142: .Pp
1.13 deraadt 143: .Pa /etc/ssh/ssh_known_hosts
1.17 jmc 144: .Sh EXAMPLES
1.34 jmc 145: Print the rsa host key for machine
146: .Ar hostname :
1.17 jmc 147: .Bd -literal
148: $ ssh-keyscan hostname
149: .Ed
150: .Pp
151: Find all hosts from the file
152: .Pa ssh_hosts
153: which have new or different keys from those in the sorted file
154: .Pa ssh_known_hosts :
155: .Bd -literal
1.35 naddy 156: $ ssh-keyscan -t rsa,dsa,ecdsa,ed25519 -f ssh_hosts | \e
1.17 jmc 157: sort -u - ssh_known_hosts | diff ssh_known_hosts -
158: .Ed
1.1 markus 159: .Sh SEE ALSO
1.4 deraadt 160: .Xr ssh 1 ,
1.1 markus 161: .Xr sshd 8
1.7 mpech 162: .Sh AUTHORS
1.21 jaredy 163: .An -nosplit
1.31 schwarze 164: .An David Mazieres Aq Mt dm@lcs.mit.edu
1.10 markus 165: wrote the initial version, and
1.31 schwarze 166: .An Wayne Davison Aq Mt wayned@users.sourceforge.net
1.10 markus 167: added support for protocol version 2.
1.17 jmc 168: .Sh BUGS
169: It generates "Connection closed by remote host" messages on the consoles
170: of all the machines it scans if the server is older than version 2.9.
171: This is because it opens a connection to the ssh port, reads the public
172: key, and drops the connection as soon as it gets the key.
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