|SSH-KEYSCAN(1)||General Commands Manual||SSH-KEYSCAN(1)|
gather SSH public keys
ssh-keyscan is a utility for gathering the
public SSH host keys of a number of hosts. It was designed to aid in
building and verifying ssh_known_hosts files, the
format of which is documented in
ssh-keyscan provides a minimal interface suitable
for use by shell and perl scripts.
ssh-keyscan uses non-blocking socket I/O
to contact as many hosts as possible in parallel, so it is very efficient.
The keys from a domain of 1,000 hosts can be collected in tens of seconds,
even when some of those hosts are down or do not run
sshd(8). For scanning, one does
not need login access to the machines that are being scanned, nor does the
scanning process involve any encryption.
The options are as follows:
ssh-keyscanto use IPv4 addresses only.
ssh-keyscanto use IPv6 addresses only.
ssh-keyscanwill read from the standard input. Input is expected in the format:
If an ssh_known_hosts file is constructed using
ssh-keyscan without verifying the keys, users will
be vulnerable to man in the
middle attacks. On the other hand, if the security model allows such
ssh-keyscan can help in the detection of
tampered keyfiles or man in the middle attacks which have begun after the
ssh_known_hosts file was created.
Print the RSA host key for machine hostname:
$ ssh-keyscan -t rsa hostname
Find all hosts from the file ssh_hosts which have new or different keys from those in the sorted file ssh_known_hosts:
$ ssh-keyscan -t rsa,dsa,ecdsa,ed25519 -f ssh_hosts | \ sort -u - ssh_known_hosts | diff ssh_known_hosts -
Using DNS to Securely Publish Secure Shell (SSH) Key Fingerprints, RFC 4255, 2006.
|March 5, 2018||OpenBSD-6.5|