2
$\begingroup$

Message authentication is ensured by using HMAC, which can be thought of as a symmetric-key construction.

Source authentication in multicast communications can be guaranteed using TESLA, which is again based on symmetric-key principles (although it basically works because of asymmetries in time).

However, neither HMAC nor TESLA ensure non-repudiation.

Is this a structural limitation of symmetric-key cryptography? Or is there some construct that ensures non-repudiation without using public/private keys?

$\endgroup$
1
$\begingroup$

Is this a structural limitation of symmetric-key cryptography? Or is there some construct that ensures non-repudiation without using public/private keys?

Non-repudiation implies that nobody other than the private key holder* could have produced the signature, which rules out symmetric constructions such as HMAC.

With a symmetric MAC (from a construction like HMAC), anyone who has the ability to verify a MAC also has the ability to construct one, so such constructions cannot be used to provide non-repudiation.

So in that sense yes, it is a limitation of symmetric-key cryptography.

While Hash-based signatures do exist, those are still an asymmetric cryptosystem with public/private keys, despite the fact that they use traditional hash functions.

Note

It is arguable whether or not signatures provide non-repudiation, which is a legal concept. It is arguable that cryptography itself is limited in the capacity to provide non-repudiation.

$\endgroup$
  • $\begingroup$ Signatures provide non-repudiation assuming 1) it is difficult to forge a signature without the algorithm used to create it (i.e. the person's brain), 2) it is easy to verify a signature visually without any secret information, and 3) it is modify a document once the signature has been added to it without being detected. It's a lot easier to trust the integer factorization problem than it is that no one is experienced at signature forgery. $\endgroup$ – forest Jun 22 '18 at 2:12

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

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