Given rsa signature scheme with emsa-pss padding shown sect

10.8. Given is an RSA signature scheme with EMSA-PSS padding as shown in Sect. 10.2.3. Describe the verification process step-by-step that has to be performed by the receiver of a signature that was EMSA-PSS encoded.

Answer:

Se=Pad Hash(M) (modN)

Definitions’ is the signature; M is the message; e and N are the public exponent and modulus from the public key; mod N means that equality is checked modulo NN; Pad is the padding function and Hash is the hashing function. Note I say ''effectively'' because sometimes the padding method is non deterministic; that makes this check slightly differ ent1 but not in way that matter s for this discussion. Now, if we were trying to forge a signature for a message M’ (with only the public key), we could certainly compute

(xe)d=x (modN)

Hand Written Solution

10. e(xi ⊕Hi−1,Hi−1)⊕Hi−1

11. e(xi ⊕Hi−1,xi)⊕Hi−1