RSA Security 5.2.2 manual 2Triple DES Encryption as Implemented in Crypto-C

Cryptography Overview

Triple DES

Triple DES executes DES three times, which triples the number of bits in an encryption key. A number of different methods achieve this function. The technique that Crypto-C uses is depicted in Figure 3-2 on page 38.

This technique is known as EDE, or “Encrypt-Decrypt-Encrypt.” The decryption process in the middle stage of Triple DES encryption provides compatibility with DES. If the three keys are the same, the Triple DES operation is equivalent to a single DES encryption. That way, an application that has only DES capabilities can still communicate with applications that use Triple DES. If the three keys are different, the decryption in the middle will scramble the message further; it will not decrypt the first stage. Triple DES decryption is the inverse operation of the previous sequence, that is, DES decryption followed by DES encryption and then another DES decryption.

8byte

message

block

24 byte Triple DES key (including parity bits)

First 8 bytes	Middle 8 bytes	Last 8 bytes
of the key	of the key	of the key
			8 byte
			message
DES	DES	DES	block
encryption	decryption	encryption

Figure 3-2Triple DES Encryption as Implemented in Crypto-C

DESX

DESX is an RSA Security proprietary extension of the DES encryption algorithm that increases the effective number of key bits from 56 to 120 bits. Crypto-C includes DESX for backward compatibility with BSAFE 1.x versions, or as a faster alternative to Triple DES.

RC2

The RC2 cipher was developed by Ronald Rivest as an alternative to DES encryption;

3 8 R S A B S A F E C r y p t o - C D e v e l o p e r ’s G u i d e