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If we assume that AES is a pseudorandom permutation (which is a standard model for block ciphers), then AES can replace the HMAC in your construction. Be aware, this only works because you have a fixed message length, i.e. the protocol must not accept nonces $> 128$bit. Besides, I guess you are aware of this but you have a shared secret key among all ...

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The short answer is that there's no link between your physical signature and any cryptographic signature. Indeed, from the high-level description of how DocuSign works and their security manifesto there's no reason to believe that any cryptography goes into the signature process itself. Note that “signature” is an overloaded word. In this post, I will refer ...

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Nimbus or Thinbus are two popular SRP implementations in Java and Javascript compute the proof of password as you describe H(A|B|S) where you can supply your own hash functions such as SHA1 or SHA256 or stronger. The actual protocol design document states H(H(N) xor H(g), H(I), s, A, B, K) where K=H(S) so that expands to H(H(N) xor H(g)|H(I)|s|A|B|H(S)). ...

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Now I would like to use a single-block AES128 for the HMAC calculation in this scheme [...] HMAC requires a hash function with a variable input size, so you cannot just use AES in it. If you want to use some other MAC instead of HMAC, you can use AES. AES ECB is a secure MAC for single block messages, so that would work. Given this answer to a ...

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