ssh 2 keys authentication

evil_empire · 06-20-2009, 05:59 PM

Hi,
ssh utilizes 2 keys(public & private) in such a manner that one only authenticates, the other only encrypts. Is this true?
Can anyone explain, which one encrypts, which one decrypts and little info on how it works?

anomie · 06-20-2009, 11:34 PM

Simple version: public key encrypts, private key decrypts.

Better version: http://en.wikipedia.org/wiki/Public-key_cryptography

For a few details on how it's implemented with openssh, see the "Authentication" section here: http://www.openbsd.org/cgi-bin/man.c...=ssh&sektion=1

evil_empire · 06-21-2009, 12:23 PM

Hi anomie,
Thank you very much for the info. I've got one more question. In my original questions is "authenticates" same as "decrypts". Will it be correct to say one key authenticates and the other encrypts? I know this question is dumb since you've already told me public key encrypts and private key decrypts.

anomie · 06-22-2009, 12:10 PM

Read through the RFC here:

http://www.ietf.org/rfc/rfc4252.txt

Quote:

7. Public Key Authentication Method: "publickey"

The only REQUIRED authentication 'method name' is "publickey"
authentication. All implementations MUST support this method;
however, not all users need to have public keys, and most local
policies are not likely to require public key authentication for all
users in the near future.

With this method, the possession of a private key serves as
authentication. This method works by sending a signature created
with a private key of the user. The server MUST check that the key
is a valid authenticator for the user, and MUST check that the
signature is valid. If both hold, the authentication request MUST be
accepted; otherwise, it MUST be rejected. Note that the server MAY
require additional authentications after successful authentication.

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