The Rijndael Algorithm: Understanding Variable Block and Key Lengths

What type of block lengths and key lengths does the Rijndael algorithm use?

A) Variable block lengths and variable key lengths

B) Fixed block lengths and fixed key lengths

C) Variable block lengths and fixed key lengths

D) Fixed block lengths and variable key lengths

Answer:

The true statement about the Rijndael algorithm is that it uses variable block lengths and variable key lengths, although only its 128-bit block length variant was adopted as AES.

Explanation: The Rijndael algorithm is best known for being selected as the Advanced Encryption Standard (AES). The statement that is true of the Rijndael algorithm is A) Rijndael uses variable block lengths and variable key lengths. The original Rijndael algorithm was designed to handle a range of block and key lengths, but only the 128-bit block length variant was adopted as the AES.

Depending on the needs, the Rijndael algorithm allows for keys of 128, 192, or 256 bits. Notably, while the AES standard specifies certain fixed parameters, the original Rijndael is more versatile with the sizes it supports. For example, AES fixed the block size at 128 bits while offering the three variable key lengths. However, the full Rijndael algorithm allows both variable blocks (128, 192, 256 bits) and variable keys (128, 192, 256 bits).