ISC 2 Credentials SSCP Question # 210 Topic 22 Discussion

The above statement is NOT true and thus the correct answer. The maximum key size on Rijndael is 256 bits.

There are some differences between Rijndael and the official FIPS-197 specification for AES.

Rijndael specification per se is specified with block and key sizes that must be a multiple of 32 bits, both with a minimum of 128 and a maximum of 256 bits. Namely, Rijndael allows for both key and block sizes to be chosen independently from the set of { 128, 160, 192, 224, 256 } bits. (And the key size does not in fact have to match the block size).

However, FIPS-197 specifies that the block size must always be 128 bits in AES, and that the key size may be either 128, 192, or 256 bits. Therefore AES-128, AES-192, and AES-256 are actually:

Key Size (bits) Block Size (bits)

AES-128 128 128

AES-192 192 128

AES-256 256 128

So in short:

Rijndael and AES differ only in the range of supported values for the block length and cipher key length.

For Rijndael, the block length and the key length can be independently specified to any multiple of 32 bits, with a minimum of 128 bits, and a maximum of 256 bits.

AES fixes the block length to 128 bits, and supports key lengths of 128, 192 or 256 bits only.

References used for this question:

http://blogs.msdn.com/b/shawnfa/archive/2006/10/09/the-differences-between-rijndael-and-aes.aspx

and

http://csrc.nist.gov/CryptoToolkit/aes/rijndael/Rijndael.pdf