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. Owing to the noisy nature of the channel, it may be overly restrictive to attempt to detect all deviations. In our formulation, we only require detecting deviations which impede the decoding of the non-deviating user's message. 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：我们引入了在通信系统中确定拜占庭用户（内部敌手）身份的问题。考虑一个两用户离散无记忆多址接入信道，其中任一用户可能偏离预设行为。由于信道的噪声特性，试图检测所有偏差可能过于严苛。在我们的表述中，仅要求检测那些阻碍非偏离用户消息解码的偏差。当无用户偏离时，需要正确解码。当某一用户偏离时，解码器必须要么输出一对消息，其中非偏离用户的消息正确，要么识别出偏离用户。用户与接收机之间不共享任何随机性。研究结果包括：对可实现通信的信道集合的表征，以及对容量区域的内界与外界。我们还表明，只要速率区域具有非空内部，容量区域便与采用随机编码（每个用户与接收机共享独立随机性）时的容量区域相同。此外，我们给出了该随机编码容量区域的一个外界。