Re: [CISSP-D] Symmetric Key and authentication.

Be careful this is a bad approach to preparing for the CISSP exam. 
The CISSP prep books out there are a great tool for CISSP candidates 
and the books consolidate a lot of information. However, they are 
not free of errors. Do not rely on an answer just because it is in a 
book.

Symmetric encryption can provide authentication but only to the 
other party in the transaction. i.e., if you and I share a key and i 
receive a message encrypted in that key, then I KNOW it came from 
you. However, I cannot take that message and show it to someone else 
and convince them that the message came from you (since either you 
OR I could have encrypted it.)

This second type of authentication is called non-repudiation and can 
only be performed through asymetric encryption.

Note: Not all asymetric encryption can enforce non-repudiation. For 
example, Diffie-Hellman algorithm was designed for key exchange only 
and does not provide non-repudiation. (It was the El Gamal algorithm 
that extended D-H to provide non-repudiation.











--- In CISSP-Discuss@yahoogroups.com, Vijay Kumar <vijaychhipa@y...> 
wrote:
> Manish
>  
> Your comments are in-line with what is logical. However the Shon 
Harris 
> book mentioned that authentication can not be had with Symmetric 
only encryption.






 
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