Pseudonymity

Pseudonymity, a word derived from pseudonym, meaning 'false name', is a state of disguised identity. The pseudonym identifies a holder, that is, one or more human beings who possess but do not disclose their true names (that is, legal identities). Most pseudonym holders use pseudonyms because they wish to remain anonymous, but anonymity is difficult to achieve, and is often fraught with legal issues. True anonymity requires unlinkability, such that an attacker's examination of the pseudonym holder's message provides no new information about the holder's true name.

Although the term is most frequently used today with regard to identity and the Internet, the concept of pseudonymity has a long history. In ancient literature it was common to write in the name of a famous person, not for concealment or with any intention of deceit; in the New Testament, the second letter of Peter is probably such. A more modern example is all of The Federalist Papers, which were signed by Publius, a pseudonym representing the trio of James Madison, Alexander Hamilton, and John Jay. The papers were written partially in response to several Anti-Federalist Papers, also written under pseudonyms. As a result of this pseudonymity, historians know that the papers were written by Madison, Hamilton, and Jay, but have not been able to discern with complete accuracy which of the three authored a few of the papers.

Pseudonymity has become an important phenomenon on the Internet and other computer networks. In computer networks, pseudonyms possess varying degrees of anonymity, ranging from highly linkable public pseudonyms (the link between the pseudonym and a human being is publicly known or easy to discover), potentially linkable non-public pseudonyms (the link is known to system operators but is not publicly disclosed), and unlinkable pseudonyms (the link is not known to system operators and cannot be determined). For example, true anonymous remailer enables Internet users to establish unlinkable pseudonyms; those that employ non-public pseudonyms (such as the now-defunct Penet remailer) are called pseudonymous remailers.

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