We introduce the problem of determining the identity of a byzantine user (internal adversary) in a communication system. We consider a two-user discrete memoryless multiple access channel where either user may deviate from the prescribed behaviour. Since small deviations may be indistinguishable from the effects of channel noise, it might be overly restrictive to attempt to detect all deviations. When neither user deviates, correct decoding is required. When one user deviates, the decoder must either output a pair of messages of which the message of the non-deviating user is correct or identify the deviating user. The users and the receiver do not share any randomness. The results include a characterization of the set of channels where communication is feasible, and an inner and outer bound on the capacity region. We also show that whenever the rate region has non-empty interior, the capacity region is same as the capacity region under randomized encoding, where each user shares independent randomness with the receiver. We also give an outer bound for this randomized coding capacity region.

翻译：本文提出了在通信系统中确定拜占庭用户（内部敌手）身份的问题。我们考虑一个双用户离散无记忆多址信道，其中任一用户都可能偏离预设行为。由于微小的偏离可能与信道噪声效应难以区分，试图检测所有偏离可能过于严格。当两个用户均未偏离时，要求实现正确解码。当某一用户偏离时，解码器必须输出一对消息，其中未偏离用户的消息需正确无误，或者识别出偏离用户。用户与接收端不共享任何随机性。研究结果包括：刻画了可实现通信的信道集合，给出了容量域的内外边界。我们还证明，只要速率域具有非空内部，其容量域就与随机化编码下的容量域相同（此时每个用户与接收端共享独立随机性）。同时给出了该随机化编码容量域的外边界。