The difference between Rijndael and AES lies primarily in their key and block sizes.

• Rijndael is a symmetric block cipher designed by Joan Daemen and Vincent Rijmen.
• It supports key and block sizes that can vary independently in multiple combinations.
• Rijndael allows for block sizes of 128, 160, 192, 224, or 256 bits, and key sizes of 128, 160, 192, 224, or 256 bits.
• This flexibility allows Rijndael to be used in various applications and provides a wider range of security options.
• AES (Advanced Encryption Standard) is a specific implementation of the Rijndael cipher that was selected as the standard symmetric encryption algorithm by the U.S. National Institute of Standards and Technology (NIST) in 2001. AES defines fixed key and block sizes, specifically:
• Key sizes: AES supports three fixed key sizes: 128 bits, 192 bits, and 256 bits.
• Block size: AES has a fixed block size of 128 bits.
• So, while Rijndael offers a broader range of key and block sizes, AES is a specific variant of Rijndael that defines standardized key and block sizes.
• Another notable difference is the number of rounds used in encryption.
• Rijndael's number of rounds is dependent on the block and key sizes chosen, whereas AES always uses a fixed number of rounds based on the block size. For AES, the number of rounds is 10 for a 128-bit block size, 12 for a 192-bit block size, and 14 for a 256-bit block size.

In summary, Rijndael is a more generalized block cipher algorithm that allows for a wide range of key and block sizes, while AES is a specific variant of Rijndael with fixed key and block sizes and a standardized number of rounds. AES is widely adopted and recognized as the industry standard for symmetric encryption.