ROT13

Because there are 26 letters in the Latin alphabet and 26 = 2 × 13, the ROT13 function is its own inverse:[2] In other words, two successive applications of ROT13 restore the original text (in mathematics, this is sometimes called an involution; in cryptography, a reciprocal cipher).

At the time of conception in an era of Ancient Roman technology, the encryption scheme was not represented by a mathematical structure.

Even if secrecy does not fail, any alien party or individual, capable of intercepting the message, could break the code by spending enough time on decoding the text through frequency analysis[2] or finding other patterns.

In the early 80s, ROT13 was supposedly used on Usenet newsgroup servers[3] This in an effort to hide potentially offensive jokes, or to obscure an answer to a puzzle or other spoiler,[4] or to fool less sophisticated spam bots[dubious – discuss].

[6] In 2001, Russian programmer Dimitry Sklyarov demonstrated that an eBook vendor, New Paradigm Research Group (NPRG), used ROT13 to encrypt their documents.

Johann Ernst Elias Bessler, an 18th-century clock maker and constructor of perpetual motion machines, pointed out that ROT13 encodes his surname as Orffyre.

[9] Because of its utter unsuitability for real secrecy, ROT13 has become a catchphrase to refer to any conspicuously weak encryption scheme; a critic might claim that "56-bit DES is little better than ROT13 these days".

through 126 '~', 94 in total, taken in the order of the numerical values of their ASCII codes, are rotated by 47 positions, without special consideration of case.

The use of a larger alphabet produces a more thorough obfuscation than that of ROT13; for example, a telephone number such as +1-415-839-6885 is not obvious at first sight from the scrambled result Z'\c`d\gbh\eggd.

Example: enciphers to The GNU C library, a set of standard routines available for use in computer programming, contains a function—memfrob()[13]—which has a similar purpose to ROT13, although it is intended for use with arbitrary binary data.