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21289cd0 | 1 | How to verify host keys using OpenSSH and DNS |
2 | --------------------------------------------- | |
3 | ||
4 | OpenSSH contains experimental support for verifying host keys using DNS | |
5 | as described in draft-ietf-secsh-dns-xx.txt. The document contains | |
6 | very brief instructions on how to test this feature. Configuring DNS | |
7 | and DNSSEC is out of the scope of this document. | |
8 | ||
9 | ||
10 | (1) Enable DNS fingerprint support in OpenSSH | |
11 | ||
2636769c | 12 | configure --with-dns |
21289cd0 | 13 | |
14 | (2) Generate and publish the DNS RR | |
15 | ||
16 | To create a DNS resource record (RR) containing a fingerprint of the | |
17 | public host key, use the following command: | |
18 | ||
19 | ssh-keygen -r hostname -f keyfile -g | |
20 | ||
21 | where "hostname" is your fully qualified hostname and "keyfile" is the | |
22 | file containing the public host key file. If you have multiple keys, | |
23 | you should generate one RR for each key. | |
24 | ||
25 | In the example above, ssh-keygen will print the fingerprint in a | |
26 | generic DNS RR format parsable by most modern name server | |
27 | implementations. If your nameserver has support for the SSHFP RR, as | |
28 | defined by the draft, you can omit the -g flag and ssh-keygen will | |
29 | print a standard RR. | |
30 | ||
31 | To publish the fingerprint using the DNS you must add the generated RR | |
32 | to your DNS zone file and sign your zone. | |
33 | ||
34 | ||
35 | (3) Enable the ssh client to verify host keys using DNS | |
36 | ||
37 | To enable the ssh client to verify host keys using DNS, you have to | |
38 | add the following option to the ssh configuration file | |
39 | ($HOME/.ssh/config or /etc/ssh/ssh_config): | |
40 | ||
41 | VerifyHostKeyDNS yes | |
42 | ||
43 | Upon connection the client will try to look up the fingerprint RR | |
44 | using DNS. If the fingerprint received from the DNS server matches | |
45 | the 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 $ |