sshfp man page

sshfp — Generate SSHFP DNS records from knownhosts files or ssh-keyscan

Syntax

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 ...] >

Description

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 tranfers (AXFR), an entire domain can be processed for all its A records.

Options

-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 an 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 editted 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

Files

~/.ssh/known_hosts

Requirements

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

Fedora: yum install python-dns

Debian: apt-get install python-dnspython

Bugs

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

Examples

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

Authors

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

Referenced By

tlsa(1).

January 2, 2015 Paul Wouters Internet / DNS