For some particular security protocol, suppose that Trudy can construct messages that appear to any observer (including Alice and/or Bob) to be valid messages between Alice and Bob. Then the protocol...

For some particular security protocol, suppose that Trudy can construct messages that appear to any observer (including Alice and/or Bob) to be valid messages between Alice and Bob. Then the protocol is said to provide plausible deniability. The idea here is that Alice and Bob can (plausibly) argue that any conversation they had using the protocol never actually occurred—it could have been faked by Trudy. Consider the following protocol, where K = II(R_A, R_B, S).