Simplify the following text for a Grade 6 native English-speaking person.
Original: Rijndael , supports block sizes of 128 , 192 , and 256 bits , although the extra block sizes were not adopted by the AES standard .
Simplified: The winner of the AES contest , Rijndael , supports key sizes of 128 , 192 , and 256 bits , but the block size is always 128 bits . The extra key sizes were not adopted by the AES standard .