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13

This is one of the earliest questions that was asked in modern cryptography. There is a proof that you cannot achieve completely fair contract signing. However, there are some reasonable alternatives. There is one direction called "gradual release" which I personally do not like. A model that I think has a lot of promise is called the "optimistic model". In ...


5

The usual methods of RSA signature with message recovery (that is, embedding a part of the message in the signature, known as the revoverable message) are those in ISO/IEC 9796-2:2010 (partial preview). There are three: Scheme 1; it is an ad-hoc scheme that essentially concatenates the recoverable message, the hash of the whole message, and a little fixed ...


4

OK, so this takes a bit of guessing, but I'm assuming the following: A is the identity of A, which can be used to select the right public key of A; Kxa() is a signing operation (with message recovery) that signs the random Ra and a tag Ts which is used as proof; Kya() is an encryption operation with the public key A, so that the session key Ks is kept ...


3

So is PKCS7 a signature format or a certificate format or both? Neither. PKCS7 is now Cryptographic Message Syntax(CMS). From the RFC 5652: This syntax is used to digitally sign, digest, authenticate, or encrypt arbitrary message content. CMS enables interoperability between different products which can operate on the same document without ...


2

When a contract in digital from is to be signed online by Alice and Bob, an issue concerning the fairness of the signing process crops up as follows: If Alice first signs the document and sends it to Bob, it means she has committed to something (e.g. ready to purchase an article from Bob at a certain price), Bob can however, if he desires, to some extent ...


1

In principle, a signature can always be used in lieu of a MAC. You use a MAC when you want the legitimate recipient of a message to be able to verify its authenticity. With a signature, everyone, including of course the legitimate recipient, can verify the authenticity of a message. The reason we use MACs at all, instead of just using signatures all the ...



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