Tweet13 uses ROT13 to obscure your updates on the Twitter micro-blogging service.
ROT13 ([HTML_REMOVED]rotate by 13 places[HTML_REMOVED]) is a simple substitution cipher used as a means of hiding spoilers, punchlines, puzzle solutions, and offensive materials from the casual glance. ROT13 has been described as the [HTML_REMOVED]Usenet equivalent of a magazine printing the answer to a quiz upside down[HTML_REMOVED]. ROT13 is a variation of the Caesar cipher, developed in ancient Rome.
ROT13 is its own inverse; that is, to undo ROT13, the same algorithm is applied. The algorithm provides no real cryptographic security and should never be used for such.