This list is drawn mostly from the book Applied Cryptography by Bruce Schneier. Alice and Bob are archetypes in cryptography; Eve is also common. Names further down the alphabet are less common.

    Alice and Bob. Generally, Alice wants to send a message to Bob. These names were used by Ron Rivest in the 1978 Communications of the ACM article presenting the RSA cryptosystem,[3] and in A Method for Obtaining Digital Signatures and Public-Key Cryptosystems published April 4, 1977, revised September 1, 1977, as technical Memo LCS/TM82.
    Carol, Carlos or Charlie, as a third participant in communications.
    Chuck, as a third participant usually of malicious intent.[4]
    Craig, the password cracker (usually encountered in situations with stored hashed/salted passwords).
    Dan or Dave, a fourth participant.
    Erin, a fifth participant. (It's rare to see Erin; E is usually reserved for Eve.)
    Eve, an eavesdropper, is usually a passive attacker. While she can listen in on messages between Alice and Bob, she cannot modify them. In quantum cryptography, Eve may also represent the environment.
    Faythe, a trusted advisor, courier or intermediary (repository of key service, courier of shared secrets. May be a machine role or human role; used infrequently. Faith or Faithful).
    Frank, a sixth participant (and so on alphabetically).
    Mallet[5][6][7][8] or Mallory,[9] a malicious attacker (less commonly called Trudy, an intruder.); unlike the passive Eve, this one is the active man-in-the-middle attacker who can modify messages, substitute their own messages, replay old messages, and so on. The difficulty of securing a system against Mallet/Mallory is much greater than against Eve.
    Oscar, an opponent, similar to Mallet/Mallory but not necessarily malicious. Could be white-hat but still wants to crack, modify, substitute, or replay messages.
    Peggy, a prover, and Victor,[9] a verifier, often must interact in some way to show that the intended transaction has actually taken place. They are often found in zero-knowledge proofs. Alternate names for the prover and the verifier are Pat and Vanna[10] after Pat Sajak and Vanna White, the hosts of Wheel of Fortune.
    Sybil, an attacker who marshals a large number of pseudonymous identities, e.g. to subvert a reputation system. See Sybil attack.
    Trent, a trusted arbitrator, is some kind of neutral third party, whose exact role varies with the protocol under discussion.
    Walter, a warden, may be needed to guard Alice and Bob in some respect, depending on the protocol being discussed.
    Wendy, a whistleblower, is an insider with privileged access who may be in a position to divulge the information.

Although an interactive proof system is not quite a cryptographic protocol, it is sufficiently related to mention the cast of characters its literature features:

    Arthur and Merlin: In interactive proof systems, the prover has unbounded computational ability and is hence associated with Merlin, the powerful wizard. He claims the truth of a statement, and Arthur, the wise king, questions him to verify the claim. These two characters also give the name for two complexity classes, namely MA and AM.
    A similar pair of characters is Paul and Carole. The characters were introduced in the solution of the Twenty Questions problem,[11] where "Paul", who asked questions, stood for Paul Erdős and "Carole", who answered them, was an anagram of "oracle". They were further used in certain combinatorial games in the roles of Pusher and Chooser respectively, and have since been used in various roles.[12]

https://en.wikipedia.org/wiki/Alice_and_Bob