1 How to verify host keys using OpenSSH and DNS 2 --------------------------------------------- 3 4 OpenSSH contains support for verifying host keys using DNS as described in 5 draft-ietf-secsh-dns-05.txt. The document contains very brief instructions 6 on how to use this feature. Configuring DNS is out of the scope of this 7 document. 8 9 10 (1) Server: Generate and publish the DNS RR 11 12 To create a DNS resource record (RR) containing a fingerprint of the 13 public host key, use the following command: 14 15 ssh-keygen -r hostname -f keyfile -g 16 17 where "hostname" is your fully qualified hostname and "keyfile" is the 18 file containing the public host key file. If you have multiple keys, 19 you should generate one RR for each key. 20 21 In the example above, ssh-keygen will print the fingerprint in a 22 generic DNS RR format parsable by most modern name server 23 implementations. If your nameserver has support for the SSHFP RR 24 you can omit the -g flag and ssh-keygen will print a standard SSHFP RR. 25 26 To publish the fingerprint using the DNS you must add the generated RR 27 to your DNS zone file and sign your zone. 28 29 30 (2) Client: Enable ssh to verify host keys using DNS 31 32 To enable the ssh client to verify host keys using DNS, you have to 33 add the following option to the ssh configuration file 34 ($HOME/.ssh/config or /etc/ssh/ssh_config): 35 36 VerifyHostKeyDNS yes 37 38 Upon connection the client will try to look up the fingerprint RR 39 using DNS. If the fingerprint received from the DNS server matches 40 the remote host key, the user will be notified. 41 42 43 Jakob Schlyter 44 Wesley Griffin 45 46 47 $OpenBSD: README.dns,v 1.2 2003/10/14 19:43:23 jakob Exp $ 48
