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diff --git a/README.dns b/README.dns new file mode 100644 index 0000000..29ecaee --- /dev/null +++ b/README.dns @@ -0,0 +1,47 @@ +How to verify host keys using OpenSSH and DNS +--------------------------------------------- + +OpenSSH contains support for verifying host keys using DNS as described +in https://tools.ietf.org/html/rfc4255. The document contains very brief +instructions on how to use this feature. Configuring DNS is out of the +scope of this document. + + +(1) Server: Generate and publish the DNS RR + +To create a DNS resource record (RR) containing a fingerprint of the +public host key, use the following command: + + ssh-keygen -r hostname -f keyfile -g + +where "hostname" is your fully qualified hostname and "keyfile" is the +file containing the public host key file. If you have multiple keys, +you should generate one RR for each key. + +In the example above, ssh-keygen will print the fingerprint in a +generic DNS RR format parsable by most modern name server +implementations. If your nameserver has support for the SSHFP RR +you can omit the -g flag and ssh-keygen will print a standard SSHFP RR. + +To publish the fingerprint using the DNS you must add the generated RR +to your DNS zone file and sign your zone. + + +(2) Client: Enable ssh to verify host keys using DNS + +To enable the ssh client to verify host keys using DNS, you have to +add the following option to the ssh configuration file +($HOME/.ssh/config or /etc/ssh/ssh_config): + + VerifyHostKeyDNS yes + +Upon connection the client will try to look up the fingerprint RR +using DNS. If the fingerprint received from the DNS server matches +the remote host key, the user will be notified. + + + Jakob Schlyter + Wesley Griffin + + +$OpenBSD: README.dns,v 1.2 2003/10/14 19:43:23 jakob Exp $ |