1
$\begingroup$

I was wondering if changing modes or primitives could affect security. For example, let's say you have encrypted data with AES-128 with CBC mode and you want to change it to AES-128 GCM, or to ASCON. What I mean by that is that you decrypt the messages then encrypt them again with the new scheme. Does that affect security in any way?

From what I've read, sometimes it affects security: if you go from CFB to CTR, then CFB_0 = Ek(IV)+P0, and when nonce||ctr = IV, then CTR_ctr = Ek(IV)+Pctr. This means that CFB_0+CTR_ctr = P0+Pctr, which gives information about the plaintexts.

Are there some other examples of modes that shouldn't be swapped? And what if we change the primitive?

$\endgroup$

1 Answer 1

1
$\begingroup$

Are there some other examples of modes that shouldn't be swapped?

Yes: https://crypto.stackexchange.com/a/105961/36960 In short, reusing one key for different purpose is generally harmful to the security assumptions and logics.

And what if we change the primitive?

I'll answer this part assuming it means changing the blockcipher or the permutation.

Different primitives generally imply domain-separation, therefore, barring logic bugs, this should be safe.

$\endgroup$

Your Answer

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

Not the answer you're looking for? Browse other questions tagged or ask your own question.