1
$\begingroup$

I have a CBC-MAC scheme using AES as the block cipher (T=H_K1(M)), which gives me a tag and a stream cipher using another key and a nonce, which gives me a cryptotext (C=E_K2(N,M)). So my question is based on a known-plaintext attack to create a valid (ciphertext, nonce, tag)-tuple. I already figured out how I can create a new message to get the same tag with a given pair (M,T):

M1 = M xor T => T = H_K1(M) = H_K1(M||M1)

Then I already figured out that I can get the keystream of a given (message, nonce, ciphertext, tag)-tuple:

KS = M xor C

But now I don't get it, how I can create another valid (nonce, ciphertext, tag)-tuple with these information.

Thanks for any ideas in advance.

Improve this question
$\endgroup$

0

Reset to default

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct.