# Tag Info

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 ...

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Alright, I'll bite. First, let me propose bounding the discussion to just the core of the protocol. In particular, let's not get hung up on: Social engineering attacks How broadly the end-to-end encryption is applied (i.e. are all conversations in the app encrypted?) The backgrounds of the inventors and reasoning for inventing the protocol Metadata ...

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BitTorrent, when encryption is used (optional in most clients), uses the Diffie-Hellman protocol for key exchange and RC4 for confidentiality. It also drops the first 1kb of data from the RC4 output as part of the specification. There is no authentication, not really enforceable anyway due to the nature of peer-to-peer sharing networks. Standard theory ...

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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 ...

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Question1: How can we show/prove that the random element only with a negligible probability can have such structure? If we assume the random oracle model and have $h: \{0,1\}^* \to \{0,1\}^n$ then we can state that $h(.)$ is equivalent to randomly sampling from $\{0,1\}^n$. Thus for a random element $r = r'||r''$ the probability that $r$ has the structure \$...

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Besides Joshua Warner's excellent answer, I do also want to point out that someone has to "roll their own crypto" at some point for there to be any designs and implementations at all. On that front, the Signal protocol was chiefly designed by Moxie Marlinspike, a cryptography and security researcher with a solid track record and credited with multiple ...

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A solution is given by Peter Ryan, Crypto Santa. In The New Codebreakers, vol. 9100 of Lecture Notes in Computer Science, pp. 543-549, Springer, 2016. http://dx.doi.org/10.1007/978-3-662-49301-4_33 An earlier version (with Sjouke Mauw and Sasa Radomirovic) can be found at http://hdl.handle.net/10993/25936 (Open access), Security protocols for Secret Santa.

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