Simon Tatham <anakin%pobox.com@localhost> writes:
Bill Sommerfeld <sommerfeld%sun.com@localhost> wrote:
> 3) if the agent is the only trusted one and the remote system is not
> trusted to see the cleartext private key, the key could be stored
> remotely in encrypted form and decrypted
> by the agent (using a passphrase or other means). (very different use
> model.)
The PuTTY team has had quite a lot of requests for a use model like
this, because it provides other desirable features such as the
ability to store all your keys encrypted until they're first needed
and ask for their passphrases as required.
This leads to an interesting twist of password authentication.
Setup: User creates a keypair, and encrypts the private half using a
passphrase. (This naturally has to be done on a trusted machine). User
transfers public key and encrypted private key to one or more servers.
Login: Client asks server for encrypted private key. User types in
passphrase to decrypt it. Key is used to sign the session id, just
like for plain publickey authentication.