Wide Mouth Frog

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The Wide Mouth Frog protocol is a computer network authentication protocol designed for use on insecure networks (the Internet for example). It allows individuals communicating over a network to prove their identity to each other while also preventing eavesdropping or replay attacks, and provides for detection of modification and the prevention of unauthorized reading. This can be proven using BAN logic.

The protocol can be specified as follows in security protocol notation, where Alice is authenticating herself to Bob using a server S:

A ightarrow S: A,{T_A, K_{AB}, B}_{K_{AS}}

S ightarrow B: {T_S, K_{AB}, A}_{K_{BS}}

Note that to prevent active attacks, some form of authenticated encryption (or message authentication) must be used.

The protocol has several problems:

* a global clock is required.
* the server has access to all keys.
* the value of the shared key between A and B is completely determined by A.
* can replay messages within period when timestamp is valid.
* A is not assured that B exists.
* The protocol is stateful. This is usually undesired because it requires more functionality and capability from the server. For example, "S" must be able to deal with situations in which "B" is unavailable.

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