Communication Model
The communication model in the bare UC framework is very basic. The message of a sending party are handed to the adversary who can replace these messages with a messages of his own choice that is delivered to the receiving party. This is also the Dolev-Yao threat model. (Based on the computational model all parties are modeled as interactive turing machines)
All communication models that add additional properties such as confidentiality, authenticity, synchronization, or anonymity are modeled using their own ideal functionality. An ideal communication functionality takes a message as input and produce a message as output. The (more limited) powers for the adversary are modeled through the (limited) capacity of the adversary to interact with this ideal functionality.
Ideal authenticated channel: For an optimal ideal authenticated channel, the ideal functionality takes a message from a party with identity as input, and outputs the same message together with the identity to the recipient and the adversary. To model the power of the adversary to delay asynchronous communication the functionality may first send a message to the adversary and would only deliver the message once it receives the command to do so as a reply.
Ideal secure channel: In an ideal secure channel, the ideal functionality only outputs the identity of the sender to both the recipient and the adversary, while the message is only revealed to the recipient. This models the requirement that a secure channel is both authenticated and private. To model some leakage about the information that is being transferred, may reveal information about the message to the adversary, e.g. the length of the message. Asynchronous communication is modeled through the same delay mechanism as for .
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