Tripcode
Tripcodes are a unique and simple way to verify your identity while still maintaining anonymity. They are most often used in 2ch-style message boards or Futaba Channel-style imageboards.
A tripcode is an input to a cryptographic hash function on the message board server, usually entered in the same field as the name.
Using the common 2ch format, name#tripcode becomes name !3GqYIJ3Obs.
Secure tripcodes
The 2ch tripcode algorithm has the flaw that, because it has no secret key, tripcodes can be reversed with a brute-force search. Some boards (such as Kareha and Shiichan) implement a secure tripcode. Secure tripcodes change on every board, but are much more resistant to preimage attacks.