Cryptography Overview
38 RSA BSAFE Crypto-C Developer’s Guide
Trip le 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.
Figure 3-2 Triple 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;
DES
encryption
DES
decryption
DES
encryption
8 byte
message
block
8 byte
message
block
First 8 bytes
of the key
Middle 8 bytes
of the key
Last 8 bytes
of the key
24 byte Triple DES key (including parity bits)