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 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 33 input. 34 35 -H Hash all hostnames and addresses in the output. Hashed names may 36 be used normally by ssh and sshd, but they do not reveal 37 identifying information should the file's contents be disclosed. 38 39 -p port 40 Port to connect to on the remote host. 41 42 -T timeout 43 Set the timeout for connection attempts. If timeout seconds have 44 elapsed since a connection was initiated to a host or since the 45 last time anything was read from that host, then the connection 46 is closed and the host in question considered unavailable. 47 Default is 5 seconds. 48 49 -t type 50 Specifies the type of the key to fetch from the scanned hosts. 51 The possible values are ``rsa1'' for protocol version 1 and 52 ``dsa'', ``ecdsa'', ``ed25519'', or ``rsa'' for protocol version 53 2. Multiple values may be specified by separating them with 54 commas. The default is to fetch ``rsa'' and ``ecdsa'' keys. 55 56 -v Verbose mode. Causes ssh-keyscan to print debugging messages 57 about its progress. 58 59SECURITY 60 If an ssh_known_hosts file is constructed using ssh-keyscan without 61 verifying the keys, users will be vulnerable to man in the middle 62 attacks. On the other hand, if the security model allows such a risk, 63 ssh-keyscan can help in the detection of tampered keyfiles or man in the 64 middle attacks which have begun after the ssh_known_hosts file was 65 created. 66 67FILES 68 Input format: 69 70 1.2.3.4,1.2.4.4 name.my.domain,name,n.my.domain,n,1.2.3.4,1.2.4.4 71 72 Output format for rsa1 keys: 73 74 host-or-namelist bits exponent modulus 75 76 Output format for rsa, dsa and ecdsa keys: 77 78 host-or-namelist keytype base64-encoded-key 79 80 Where keytype is either ``ecdsa-sha2-nistp256'', ``ecdsa-sha2-nistp384'', 81 ``ecdsa-sha2-nistp521'', ``ssh-ed25519'', ``ssh-dss'' or ``ssh-rsa''. 82 83 /etc/ssh/ssh_known_hosts 84 85EXAMPLES 86 Print the rsa host key for machine hostname: 87 88 $ ssh-keyscan hostname 89 90 Find all hosts from the file ssh_hosts which have new or different keys 91 from those in the sorted file ssh_known_hosts: 92 93 $ ssh-keyscan -t rsa,dsa,ecdsa -f ssh_hosts | \ 94 sort -u - ssh_known_hosts | diff ssh_known_hosts - 95 96SEE ALSO 97 ssh(1), sshd(8) 98 99AUTHORS 100 David Mazieres <dm@lcs.mit.edu> wrote the initial version, and Wayne 101 Davison <wayned@users.sourceforge.net> added support for protocol version 102 2. 103 104BUGS 105 It generates "Connection closed by remote host" messages on the consoles 106 of all the machines it scans if the server is older than version 2.9. 107 This is because it opens a connection to the ssh port, reads the public 108 key, and drops the connection as soon as it gets the key. 109 110OpenBSD 5.5 January 28, 2014 OpenBSD 5.5 111