On 6/13/07, Siddhesh Poyarekar siddhesh.poyarekar@gmail.com wrote:
On 6/13/07, Dinesh Joshi dinesh.a.joshi@gmail.com wrote:
Get your facts straight before you reply. a message encrypted with a 128 bit key DES is no more secure than a 64 bit key DES. Actually the length of the key is only 56 bit in the latter case.
Please cite a source for this. I'd like to know how DES is done with a 128 bit key.
The Data Encryption Standard (DES) implies the use of a 56 bit key. Change the key length and you'll have to change multiple parameters of the algorithm.
@Siddhesh: You're right. The two basic steps - substitution and permutation - are designed carefully for 64 bit blocks. Increasing it for higher number of bits will be non-trivial in that guaranteeing its security is difficult.
@Dinesh: By definition, a brute-force attack is just cycling through all the possible keys. Therefore, in general, greater the bits in the key, the more combinations that require to be tested and hence harder the brute-force attack. This is independent of DES or 3-DES or any other key-based encryption algorithm.
Parijat