Can CFB mode of block cipher be used as a commutative encryption?
Is it possible to use CFB mode of AES block cipher to create commutative encryption?
With CTR it is possible but not secure.
Cryptography Stack Exchange is a question and answer site for software developers, mathematicians and others interested in cryptography. It only takes a minute to sign up.Sign up to join this community
No, because CFB isn't commutative.
You can see this by looking at the decryption of double-CFB encrypted ciphertext. Even assuming a constant IV (so single-use keys), if you decrypt in the wrong order it cannot work, since the ciphertext is used as input into the block cipher and will differ from what was used with that key when encrypting.
The exception, of course, is single block messages, where CFB effectively reduces to CTR and has similar commutativity and (in)security, with the latter depending on how it is used.