As a break or decipher (colloquially often called " crack ") is in the cryptanalysis , ie in the branch of science of cryptology , which deals with the deciphering of secret writing is concerned, the activity of a cryptanalyst or code breaker ( English Codebreaker called), a ciphertext without knowledge the key to wrest the message, so it into plain text reconvert. After a secret message has been successfully broken, it can be "read" in jargon , a ciphertext is "solved", a broken procedure is "uncovered" and can be "read along".
Often and imprecisely, the term "decrypt" is used synonymously with "breaking". However, it makes sense to refer to only the authorized activity of the legitimate recipient of the message who is in possession of the key as decryption and not the breaking of the ciphertext (without the key).
Besides cryptanalytic methods, ie the direct " attack " on the ciphertext, by example, frequency analysis , pattern matching or calculating the coincidence index , it is possible to break in by the to the text in the simplest case encryption used secret password guessing is.
Famous examples of the breaking of encryption methods are the deciphering of the German key machine Enigma and the cryptanalysis of the Lorenz machine by British code breakers in Bletchley Park, England, during World War II .
A cryptosystem can be described as "unbreakable", "indecipherable" or "unbreakable" if it cannot be broken in theory or at least in practice. This is certainly only known for the so-called one-time pad (one-time key procedure). For other methods, such as AES or RSA , which are currently considered unbreakable, this assessment could change sooner or later due to fundamentally better mathematical methods or significantly faster computers. For the Vigenère cipher , which at the time was called Le Chiffre indéchiffrable (German: "The undecipherable encryption") and which was considered unbreakable for more than two hundred years, or for the Enigma, which was considered unbreakable by the German military , as we know today, this is certainly not the case.
- High Command of the Wehrmacht: General key rules for the Wehrmacht . Berlin 1944, p. 5 f. cdvandt.org (PDF; 0.9 MB) accessed August 26, 2010
- Claude Shannon : Communication Theory of Secrecy Systems . In: Bell System Technical Journal , Vol. 28, 1949 (October), p. 662.netlab.cs.ucla.edu (PDF; 0.6 MB) Retrieved: July 17, 2008.
- Jörn Müller-Quade : Hieroglyphs, Enigma, RSA - A history of cryptography . Faculty of Computer Science at the University of Karlsruhe, p. 36, ira.uka.de (PDF; 2.1 MB) accessed: May 17, 2009.