RSA / DSS (keylenghts)

Pete Chown
Thu, 21 Sep 2000 17:53:38 +0100

Ralf Senderek wrote:

> if you double the size of a DSS-key not one additional secret key value
> is added because the amount of possible secret keys is limited by the
> size of the hash-function (160 bits), Only the mathematical operation
> will use a longer key (as modulus) and consequently takes more time.
This is true, but hopefully it makes cryptanalysis more difficult. By the time you get to a 1024-bit modulus, it will take roughly the same amount of time to solve either of the two possible discrete logarithm problems. With a 512-bit modulus, it is (counterintuitively) much easier to attack the 512-bit discrete logarithm problem rather than the 160-bit one, because they have different characteristics. (I am sure you already knew that though.) There is no reason why you couldn't have a DSA key longer than 1024 bits (that I am aware of). However, to get any benefit from this you would need to make the other modulus longer than 160 bits. This would mean using a hash function other than SHA-1, for example Tiger/192. -- Pete -- Archive is at - Unsubscribe by sending mail with a subject of "unsubscribe" to