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sshfp - Man Page

Generate SSHFP DNS records from knownhosts files or ssh-keyscan


sshfp [-k <knownhosts_file>] [-d] [-a] [--type <algo>] [--digest <digest>] [<host1> [host2 ...]]

sshfp -s [-p <port>] [-d] [-a] [--type <algo>] [--digest <digest>] [-n <nameserver>] <domain1> [domain2] <host1> [host2 ...] >


sshfp generates RFC-4255 SSHFP DNS records based on the public keys stored in a known_hosts file, which implies the user has previously trusted this key, or public keys can be obtained by using ssh-keyscan (1). Using ssh-keyscan (1) implies a secure path to connect to the hosts being scanned. It also implies a trust in the DNS to obtain the IP address of the hostname to be scanned. If the nameserver of the domain allows zone transfers (AXFR), an entire domain can be processed for all its A records.


-s / --scan <hostname1> [hostname2 ...]

Scan hosts or domain for public SSH keys using ssh-keyscan

-k / --knownhosts <knownhosts_file> <hostname1> [hostname2 ...]

Obtain public SSH keys from a known_hosts file. Defaults to using ~/.ssh/known_hosts

-a / --all

Scan all hosts in the known_hosts file when used with -k. When used with -s, it will attempt a zone transfer (AXFR) to obtain all A records in the domain specified.

-d / --trailing-dot

Add a trailing dot to the hostname in the SSHFP records. It is not possible to determine whether a known_hosts or dns query is for a FQDN (eg www.redhat.com) or not (eg www) or not (unless -d domainname -a is used, in which case a trailing dot is always appended). Non-FQDN get their domainname appended through /etc/resolv.conf These non-FQDN will happen when using a non-FQDN (eg sshfp -k www) or known_hosts entries obtained by running ssh www.sub where .domain.com is implied. When -d is used, all hostnames not ending with a dot, that at least contain two parts in their hostname (eg www.sub but not www get a trailing dot. Note that the output of sshfp can also just be manually edited for trailing dots.

-o / --output <filename>

Write to filename instead of stdout

-p / --port <portnumber>

Use portnumber for scanning. Note that portnumbers do NOT appear in SSHFP records.

-h / --help

Output help information and exit.

-v / --version

Output version information and exit.

-q / --quiet

Output less miscellany to stderr




sshfp requires python-dns (http://www.pythondns.org)

Fedora: yum install python-dns

Debian: apt-get install python-dnspython


if a domain contains non-working glue A records, then ssh-keyscan aborts instead of skipping the single broken entry.

This program can look up hashed hostnames in a known_hosts file if a recent-enough ssh-keygen is present


typical usage:

sshfp (implies -k -a)

sshfp -a -d (implies -k)

sshfp -k bofh.nohats.ca (from known_hosts)

sshfp -s bofh.nohats.ca (from a scan to the host)

sshfp -k ~paul/.ssh/known_hosts bofh.nohats.ca www.openswan.org -o /tmp/mysshfp.txt

sshfp -a -d -d nohats.ca -n ns0.nohats.ca >> /var/named/primary/nohats.ca

See Also

ssh-keyscan(1)ssh(1)tlsa(1) and RFC-4255


Paul Wouters <pwouters@redhat.com>, Jacob Appelbaum <jacob@appelbaum.net>, James Brown <jbrown@yelp.com>

Referenced By


January 2, 2015 Paul Wouters Internet / DNS