Score:0

Hybrid Authentications

br flag

Is there a reason why we can't combine private key MAC with digital signature to get a hybrid authentication scheme?

Is it because of the computational assumptions that digital signatures have?

Edit: (Clarification) I don't intend to combine them, it's a problem on a past final that I am doing as practice but I don't know how to explain why we can't combine them.

cn flag
The main issue here is that you do not define *how* you would combine them, nor what the *goal* would be.
Score:1
my flag

Is there a reason why we can't combine private key MAC with digital signature to get a hybrid authentication scheme?

How do you intend to combine them?

If you assume that the signer and the verifier both share the private MAC key, well, yes, we can - however, we still retain the problem of the shared secret MAC key, and so adding the digital signature didn't improve anything, as it did not remove the main drawback of MACs (which is the need to share the MAC key securely).

If you assume that the verifier somehow reconstructs the MAC key as a part of the verification process, well, a forger can also reconstruct the MAC key, and so adding the MAC didn't improve anything (as the forger can easily forge the MAC tag using the key he knows).

paul lacher avatar
br flag
I don't intend to combine them, it's a problem on a past final that I am doing as practice but I didn't know how to explain why we can't combine them.
kelalaka avatar
in flag
isn't non-repudiation an improvement over (mutual) authentication? Of course, if we have the digital signature, why do we need keyed-MAC?
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