Malicious user

A malicious user is a legitimate user of one-to-one E2EE, but his adversary tries to break one of the subsequently defined security goals of the other E2EE session by maliciously manipulating the protocol. A malicious user is much weaker than an E2EE adversary, because any user is potentially a malicious user.

A malicious user can collude with an E2EE adversary, or the E2EE adversary him/herself can be a malicious user.