Which of the following is NOT a property of the Rijndael block cipher algorithm?

The correct answer is C. Maximum key size is 512 bits. The Rijndael algorithm (which became AES) supports key sizes of 128, 192, or 256 bits - all multiples of 32 bits - and block sizes in the same range up to 256 bits. A 512-bit key size is NOT supported; the maximum key size is 256 bits. The other statements are true: key sizes…

Submitted by wei.xz· Apr 18, 2026Cryptography

Question

Options

AThe key sizes must be a multiple of 32 bits
BMaximum block size is 256 bits
CMaximum key size is 512 bits
DThe key size does not have to match the block size

How the community answered

(22 responses)

A
5% (1)
C
91% (20)
D
5% (1)

Explanation

The Rijndael algorithm (which became AES) supports key sizes of 128, 192, or 256 bits - all multiples of 32 bits - and block sizes in the same range up to 256 bits. A 512-bit key size is NOT supported; the maximum key size is 256 bits. The other statements are true: key sizes must be multiples of 32 bits, the maximum block size is 256 bits, and the key size does not need to match the block size. When standardized as AES, NIST fixed the block size to 128 bits but retained the three key size options.

Topics

#Rijndael#AES#Block Ciphers#Key Sizes

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