Module ARC2

RC2 symmetric cipher

RC2 (Rivest's Cipher version 2) is a symmetric block cipher designed by Ron Rivest in 1987. The cipher started as a proprietary design, that was reverse engineered and anonymously posted on Usenet in 1996. For this reason, the algorithm was first called Alleged RC2 (ARC2), since the company that owned RC2 (RSA Data Inc.) did not confirm whether the details leaked into public domain were really correct.

The company eventually published its full specification in RFC2268.

RC2 has a fixed data block size of 8 bytes. Length of its keys can vary from 8 to 128 bits. One particular property of RC2 is that the actual cryptographic strength of the key (effective key length) can be reduced via a parameter.

Even though RC2 is not cryptographically broken, it has not been analyzed as thoroughly as AES, which is also faster than RC2.

New designs should not use RC2.

As an example, encryption can be done as follows:

>>> from Crypto.Cipher import ARC2
>>> from Crypto import Random
>>>
>>> key = b'Sixteen byte key'
>>> iv = Random.new().read(ARC2.block_size)
>>> cipher = ARC2.new(key, ARC2.MODE_CFB, iv)
>>> msg = iv + cipher.encrypt(b'Attack at dawn')