AES with a longer key instead of key expansion?

Asked Jun 12 '20 at 16:42

Active Jun 12 '20 at 16:54

Viewed 38 times

What are the disadvantages of using AES-256 with 240-byte key (which scrypt/bcrypt/argon2/pbkdf2 can easily output) instead of an expanded 256-bit key?

The only disadvantage I can think of is "no more hardware acceleration". This is not important for a fair comparison, are there other disadvantages?

EDIT: This is about replacing round keys.

edited Jun 12 '20 at 16:54

asked Jun 12 '20 at 16:42

MCCCS

4

You cannot use a 240 byte key with AES. Key sizes are fixed to 128, 192, and 256 bits (16, 24, 32 bytes respectively). If you use a key derivation function, its output must either be the desired length or it must be truncated. – Marc Jun 12 '20 at 16:48
@Marc I mean separating an 240-byte key to arrays of 16-bytes and using a different array of 16-bytes in every round instead of KeyExpansion output of an 256 bit key. – MCCCS Jun 12 '20 at 16:52
4

Gotcha. You want to replace the AES key schedule with an existing KDF. Performance aside, this might mitigate some of the attacks due to the weak key schedule but I don't think those are so impressive to begin with. – Marc Jun 12 '20 at 17:09
3

AES key schedule. Does it use a KDF to generate the round keys? – kelalaka Jun 12 '20 at 17:15
@Marc @ kelalaka thanks my question is now answered. – MCCCS Jun 13 '20 at 09:22

AES with a longer key instead of key expansion?

0 Answers0