John Young wrote:
>
> Last summer, at a workshop on "Security Metrics," conducted
> by NIST's Computer System Security and Privacy Advisory
> Board, Landgrave Smith, Institute of Defense Analysis, reported
> on a pilot study of "the metrics used for determining the
> strength of cryptography."
>
> http://csrc.nist.gov/csspab/june13-15/sec-metrics.html (the workshop)
>
> http://csrc.nist.gov/csspab/june13-15/Smith.pdf (Smith's presentation)
>
> Five catergories of algorithm strength were established for
> the pilot:
>
> Unconditionally Secure (US)
> Computationally Secure (CS)
> Conditionally Computationally Secure (CCS)
> Weak (W)
> Very Weak (VW)
>
> Smith stated: "A cipher is Unconditionally Secure (US)
> if no matter how much ciphertext is intercepted, there
> is not enough information in the ciphertext to
> determine the plaintext uniquely."
>
> No examples for this strength were given, and it was
> not clear from Smith's presentation whether there is
> such a cipher or the category was only provided
> as a theoretical premise.
>
> Question: is there a cipher that is Unconditionally
> Secure?
One-time pads.
> A cipher is Computationally Secure (CS) if it cannot
> be broken by systematic analysis with available
> resources in a short enough time to permit
> exploitation. Examples: DES and 3 DES.
Wrong, DES is Weak.
> A cipher is Conditionally Computationally Secure
> (CCS) if the cipher could be implemented with keys
> that are not quite "long enough" or with not quite
> "enough" rounds to warrant a CS rating. Examples:
> SKIPJACK and RSA.
>
> A Weak (W) cipher can be broken by a brute force
> attack in an acceptable length of time with an
> "affordable" investment in cryptanalytic resources
> (24 hours and $200K). No examples.
>
> A Very Weak (VW) cipher is one that can be broken
> by determining the key systematically in a short
> period of time with a small investment (8 hours
> and $20K). No examples.
An example of this would be the cipher used on DVDs, or the mobile phone
one, both of whose names I've forgotten.
Cheers,
Ben.
--
http://www.apache-ssl.org/ben.html
"There is no limit to what a man can do or how far he can go if he
doesn't mind who gets the credit." - Robert Woodruff
