bug or feature with ssh-keygen and user CAs?

Mattias Lindgren mlindgren at runelind.net
Thu May 8 10:50:25 EST 2014

I have confirmed this behavior from OpenSSH 6.6 in OS X (from MacPorts) and 6.6 in Ubuntu.  I have set up a SSH Certificate authority, and as such I put in the following line at the top of my known_hosts file

@cert-authority *.mydomain.com ssh-rsa <public key>

Below this are all my hashed entries for various other hosts that I’ve contacted over the years.  

Every once in a while I’ll rebuild a box in my environment, and the ssh key will change.  To clean up my known_hosts file to allow me to re-insert the new entry, I will do ssh-keygen -R <ip>.  This has the unintended consequence of matching on the offending entry in the known_hosts file *and* my cert-authority entry:

$ ssh-keygen -R
# Host found: line 1 type RSA
# Host found: line 512 type ECDSA
/Users/mlindgren/.ssh/known_hosts updated.
Original contents retained as /Users/mlindgren/.ssh/known_hosts.old

Am I missing something fundamental here?



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