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The Crypt_des module

DES, created by the NSA, is a 64 bit block cipher, so the following applies:

module Cryptsystem : Cryptsystem_64.T;;
module Cryptmodes : Cryptmodes_64.T with
 type key = Cryptsystem.key;;

Key management functions:

Although only 56 bits count a DES key is written with 64 bits. The extra bits are used for parity checking.

val check_parity : string -> unit

Checks that the parity of the key given as string is ok. The string must have a length of 8 characters.

val set_parity : string -> string

Sets the parity bits in the given key and returns a new string.

- DES has been heavily studied and seems to have a rather good design - DES has only 56 bit keys (this means DES should be considered a weak algorithm today, but the variant 3DES is still secure) - DES has been designed to be implemented in hardware, and software implementations are relatively slow - DES is an ANSI and (indirectly) an ISO standard. - There are very few weak keys.


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