README.dns revision 124208
1How to verify host keys using OpenSSH and DNS 2--------------------------------------------- 3 4OpenSSH contains experimental support for verifying host keys using DNS 5as described in draft-ietf-secsh-dns-xx.txt. The document contains 6very brief instructions on how to test this feature. Configuring DNS 7and DNSSEC is out of the scope of this document. 8 9 10(1) Enable DNS fingerprint support in OpenSSH 11 12 configure --with-dns 13 14(2) Generate and publish the DNS RR 15 16To create a DNS resource record (RR) containing a fingerprint of the 17public host key, use the following command: 18 19 ssh-keygen -r hostname -f keyfile -g 20 21where "hostname" is your fully qualified hostname and "keyfile" is the 22file containing the public host key file. If you have multiple keys, 23you should generate one RR for each key. 24 25In the example above, ssh-keygen will print the fingerprint in a 26generic DNS RR format parsable by most modern name server 27implementations. If your nameserver has support for the SSHFP RR, as 28defined by the draft, you can omit the -g flag and ssh-keygen will 29print a standard RR. 30 31To publish the fingerprint using the DNS you must add the generated RR 32to your DNS zone file and sign your zone. 33 34 35(3) Enable the ssh client to verify host keys using DNS 36 37To enable the ssh client to verify host keys using DNS, you have to 38add the following option to the ssh configuration file 39($HOME/.ssh/config or /etc/ssh/ssh_config): 40 41 VerifyHostKeyDNS yes 42 43Upon connection the client will try to look up the fingerprint RR 44using DNS. If the fingerprint received from the DNS server matches 45the remote host key, the user will be notified. 46 47 48 Jakob Schlyter 49 Wesley Griffin 50 51 52$OpenBSD: README.dns,v 1.1 2003/05/14 18:16:20 jakob Exp $ 53