1SSH-KEYSCAN(1) OpenBSD Reference Manual SSH-KEYSCAN(1) 2 3NAME 4 ssh-keyscan - gather ssh public keys 5 6SYNOPSIS 7 ssh-keyscan [-46Hv] [-f file] [-p port] [-T timeout] [-t type] 8 [host | addrlist namelist] ... 9 10DESCRIPTION 11 ssh-keyscan is a utility for gathering the public ssh host keys of a 12 number of hosts. It was designed to aid in building and verifying 13 ssh_known_hosts files. ssh-keyscan provides a minimal interface suitable 14 for use by shell and perl scripts. 15 16 ssh-keyscan uses non-blocking socket I/O to contact as many hosts as 17 possible in parallel, so it is very efficient. The keys from a domain of 18 1,000 hosts can be collected in tens of seconds, even when some of those 19 hosts are down or do not run ssh. For scanning, one does not need login 20 access to the machines that are being scanned, nor does the scanning 21 process involve any encryption. 22 23 The options are as follows: 24 25 -4 Forces ssh-keyscan to use IPv4 addresses only. 26 27 -6 Forces ssh-keyscan to use IPv6 addresses only. 28 29 -f file 30 Read hosts or addrlist namelist pairs from this file, one per 31 line. If - is supplied instead of a filename, ssh-keyscan will 32 read hosts or addrlist namelist pairs from the standard input. 33 34 -H Hash all hostnames and addresses in the output. Hashed names may 35 be used normally by ssh and sshd, but they do not reveal 36 identifying information should the file's contents be disclosed. 37 38 -p port 39 Port to connect to on the remote host. 40 41 -T timeout 42 Set the timeout for connection attempts. If timeout seconds have 43 elapsed since a connection was initiated to a host or since the 44 last time anything was read from that host, then the connection 45 is closed and the host in question considered unavailable. 46 Default is 5 seconds. 47 48 -t type 49 Specifies the type of the key to fetch from the scanned hosts. 50 The possible values are ``rsa1'' for protocol version 1 and 51 ``dsa'', ``ecdsa'' or ``rsa'' for protocol version 2. Multiple 52 values may be specified by separating them with commas. The 53 default is ``rsa''. 54 55 -v Verbose mode. Causes ssh-keyscan to print debugging messages 56 about its progress. 57 58SECURITY 59 If an ssh_known_hosts file is constructed using ssh-keyscan without 60 verifying the keys, users will be vulnerable to man in the middle 61 attacks. On the other hand, if the security model allows such a risk, 62 ssh-keyscan can help in the detection of tampered keyfiles or man in the 63 middle attacks which have begun after the ssh_known_hosts file was 64 created. 65 66FILES 67 Input format: 68 69 1.2.3.4,1.2.4.4 name.my.domain,name,n.my.domain,n,1.2.3.4,1.2.4.4 70 71 Output format for rsa1 keys: 72 73 host-or-namelist bits exponent modulus 74 75 Output format for rsa, dsa and ecdsa keys: 76 77 host-or-namelist keytype base64-encoded-key 78 79 Where keytype is either ``ecdsa-sha2-nistp256'', ``ecdsa-sha2-nistp384'', 80 ``ecdsa-sha2-nistp521'', ``ssh-dss'' or ``ssh-rsa''. 81 82 /etc/ssh/ssh_known_hosts 83 84EXAMPLES 85 Print the rsa host key for machine hostname: 86 87 $ ssh-keyscan hostname 88 89 Find all hosts from the file ssh_hosts which have new or different keys 90 from those in the sorted file ssh_known_hosts: 91 92 $ ssh-keyscan -t rsa,dsa,ecdsa -f ssh_hosts | \ 93 sort -u - ssh_known_hosts | diff ssh_known_hosts - 94 95SEE ALSO 96 ssh(1), sshd(8) 97 98AUTHORS 99 David Mazieres <dm@lcs.mit.edu> wrote the initial version, and Wayne 100 Davison <wayned@users.sourceforge.net> added support for protocol version 101 2. 102 103BUGS 104 It generates "Connection closed by remote host" messages on the consoles 105 of all the machines it scans if the server is older than version 2.9. 106 This is because it opens a connection to the ssh port, reads the public 107 key, and drops the connection as soon as it gets the key. 108 109OpenBSD 5.0 August 31, 2010 OpenBSD 5.0 110