5.3. Case study: the Wide-Mouthed-Frog protocol

In this section we consider the example of the Wide-Mouthed-Frog protocol:

Here the server shares keys ServerKey(a) and ServerKey(b) with a and b, respectively; the protocol aims to establish a session key kab between a and b, and to authenticate a to b. The agent a invents a session key and sends it to s along with a timestamp ts1; s then forwards the key to b along with a new timestamp ts2.

Timestamps are used so that agents receive evidence that the messages they receive were created recently. We note in passing that for this mechanism to work it is necessary for the different agents’ clocks ...

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