ROT13

ROT13 (English rotate by 13 places to in German as " rotate by 13 places ") is a Caesar cipher (also called shift cipher ), with the simple way texts can be encrypted. This is done by replacing letters - in ROT13 in particular, each letter of the Latin alphabet is replaced by the or behind it in the alphabet by 13 places before letters.

The name comes from the ROT13 Usenet in the early 1980s. ROT13 is not intended for secure encryption, it is, in contrast, even often cited as an example of a weak, insecure encryption. Rather, ROT13 is used to make text unreadable, so obscure, so that an act of the reader is required to read the original text. ROT13 can therefore be compared with solutions of puzzles in magazines that are printed upside down so that they can be read by mistake immediately.

ROT13 itself uses only the 26 letters of the Latin alphabet, but there are more complex methods, also note the numbers and special characters.

Name History and use of the Internet

The name ROT13 for the relatively trivial algorithm guesses originally joined According to the newsgroup net.jokes. There were attempts to preserve the readers from potentially offensive jokes in particular, but a single category was rejected because there is no special place for this rather rejected posts should be created. Thus the simple process ROT13 was used to directly protect readers from these types of jokes. It also punch lines of the jokes were encrypted so that they could not be read inadvertently too early.

The method has since been used in various areas for the protection of the readership, so that the reader does not accidentally read something they do not want to read; apart from the aforementioned experiment, a voluntary youth protection, for example, to protect against spoilers (about content description of a film). Some e -mail programs, text editors and many newsreaders offer a ROT13 function.

Algorithm

ROT13 has over other ciphers ( ROT, so compared to a shift by n ≠ 13 characters of the alphabet ) has the advantage that the encryption and decryption runs identical, so mathematically there is an involution. If an already once ciphertext re-encrypted, so it is therefore decrypted. Widespread therefore is the joke of "double ROT13 encrypted " content (sometimes called ROT -26 ).

Due to the simplicity of the algorithm is encrypted texts may be tuned manually - decrypt relatively easily and quickly as well as by simple programs - for example, using a table. On UNIX systems, by default, there is a command line program called tr ( for eng. Literate trans ), which can be used for encryption and decryption.

Tr A-Za -z N -ZA -Mn- za- m A method for automatic decryption has been incorporated into numerous newsreader. Because ROT13 letters of the alphabet only replaced again with letters, caused this method to newsreaders no mistake as other simple ciphers, where the letters were replaced by special characters, which could not manage the software.

For encryption and decryption, the following table can be used:

It the above letter is replaced respectively by the below it - both for encryption and for decryption.

Example

An example is the partial encryption of a joke, so that the beginning of wit and Pointe remain separate:

What makes a Ostfriese with a knife in his hand on the dike? Re jvyy va Frr fgrpura! By using ROT13 on the second line of the punch line is disclosed:

What makes a Ostfriese with a knife in his hand on the dike? He wants to set sail! ROT13 Encryption Technique

ROT13 is a special case of the historical encryption method, which used the Roman general Gaius Julius Caesar more than 2000 years ago and is known as the Caesar cipher. ROT13 is a solid Caesar shift by 13 letters (equivalent to the M key ) and is therefore not suitable as a secure encryption. This method can be very quickly unmasked and broken with the simplest cryptanalytic methods such as the investigation of the letters or the frequency analysis for common letter combinations.

The sole purpose of ROT13 is therefore the that the recipient of a message must make the conscious decision to read the encrypted section. As a manifestly unsafe ROT13 encryption method is that designation to buzzword for insecure encryption was.

ROT13 variations

Since it is also useful in some cases, that numbers can not be recognized at first glance, also a procedure called ROT18 has been developed which includes the digits from 0 to 9 inclusive with the capital letter in lowercase but is identical with ROT13. ROT18 is, however, not supported by any standard e - mail program or newsreader. Alternatively, there is the method ROT5, the specially treated the numbers and they continue to push to five digits. The even less common ROT47 algorithm again applies the ROT13 method known to all ASCII characters between 33 ("!" ) And 126 ("~ ").