Difference between SSL and Kerberos authentication?

Question

I am trying to understand what\'s the actual difference between SSL and Kerberos authentications, and why sometimes I have both SSL traffic and Kerberos. Or does Kerberos use S

Answer 1

To put simply, Kerberos is a protocol for establishing mutual identity trust, or authentication, for a client and a server, via a trusted third-party, whereas SSL ensures authentication of the server alone, and only if its public key has already been established as trustworthy via another channel. Both provides secure communication between the server and client.

More formally (but without getting into mathematical proofs), given a client C, server S, and a third-party T which both C and S trust:

After Kerbeos authentication, it is established that:

• C believes S is who it intended to contact
• S believes C is who it claims to be
• C believes that it has a secure connection to S
• C believes that S believes it has a secure connection to C
• S believes that it has a secure connection to C
• S believes that C believes it has a secure connection to S

SSL, on the other hand, only establishes that:

• C believes S is who it intended to contact
• C believes it has a secure connection to S
• S believes it has a secure connection to C

Clearly, Kerberos establishes a stronger, more complete trust relationship.

Additionally, to establish the identity of S over SSL, C needs prior knowledge about S, or an external way to confirm this trust. For most people's everyday use, this comes in the form of Root Certificates, and caching of S's certificate for cross-referencing in the future.

Without this prior knowledge, SSL is susceptible to man-in-the-middle attack, where a third-party is able to pretend to be S to C by relaying communication between them using 2 separate secure channels to C and S. To compromise a Kerberos authentication, the eavesdropper must masquerade as T to both S and C. Note, however, that the set of trusts is still unbroken according to the goal of Kerberos, as the end-state is still correct according to the precondition "C and S trusts T".

Finally, as it has been pointed out in a comment, Kerberos can be and has been extended to use SSL-like mechanism for establishing the initial secure connection between C and T.