RSA Laboratories

3.6.2 What is RC2?

RC2 is a variable key-size block cipher designed by Ronald Rivest for RSA Data Security (now RSA Security). "RC" stands for "Ron's Code" or "Rivest's Cipher." It is faster than DES and is designed as a "drop-in" replacement for DES (see Section 3.2). It can be made more secure or less secure than DES against exhaustive key search by using appropriate key sizes. It has a block size of 64 bits and is about two to three times faster than DES in software. An additional string (40 to 88 bits long) called a salt can be used to thwart attackers who try to precompute a large look-up table of possible encryptions. The salt is appended to the encryption key, and this lengthened key is used to encrypt the message. The salt is then sent, unencrypted, with the message. RC2 and RC4 have been widely used by developers who want to export their products; more stringent conditions have been applied to DES exports.

An agreement between the Software Publishers Association (SPA) and the United States government has been given RC2 and RC4 (see Question 3.6.3) special status by means of which the export approval process has been simpler and quicker than the usual cryptographic export process. Due to dramatically relaxed restrictions on export regulations as of January 2000, the greater part of this agreement will probably no longer be needed.

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