openssh keys in ldap

[Doug E Manton]

> If the keys stay encrypted (not counting ssl) until ssh-add decrypts 
them (in the
> same manner that it decrypts the private keys off the filesystem). Would 
we need to
> trust the LDAP server or transport protocol.  What problems would we 
encounter with
> this?

The private key encryption is a fallback position -- the first line of 
protection is to keep the key private!  This is the same reason that most 
UNIX systems use shadow password files.

If we rely on the key encryption, can we trust our users to select strong 
passphrases?  We can't enforce passphrase rules because of the nature of 
key generation.  Dictionary attacks demonstrate that users will do 
anything in their power to select poor passphrases!

My personal preference is the exact opposite approach.  Stick the private 
key onto some kind of smartcard.  The ideal smartcard would run the 
SSH-agent itself and never reveal the key to anyone, you just initialise 
it with your passphrase before use -- and when you unplug it or a timeout 
occurs, it forgets the key and prompts upon next use.

Doug.