Signatures are when you want to produce a proof verifiable by third party without having to entrust these third parties with anything.Īpplication: a CA (like Verisign or Thawte or whatever) issues a certificate to a SSL server. ![]() With signatures, you can make the verification key public, while keeping the generation key private. With a MAC, any entity who can verify a MAC value necessarily has the power to generate MAC values of its own. Thus, signatures dissociate the generation and verification powers. With a signature, the verification key K 2 is mathematically linked with K 1 but not identical, and it is unfeasible to recompute K 1 from K 2 or to generate valid signatures when you only know K 2. With a MAC, keys K 1 and K 2 are identical (or can be trivially recomputed from each other). ![]() ![]() Verification: given the message m, a key K 2 and the MAC value or signature s, verify that they correspond to each other (the MAC value or signature is valid for the message m, using verification key K 2).Generation: given the message m and a key K 1, compute the MAC value or signature s.In both MAC and digital signature schemes, you have two algorithms:
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