Spell key

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As message key in is cryptology one for each "saying" to be selected individually cryptographic keys called. (In jargon, “Spruch” means encrypted secret messages such as documents , telegrams or radio messages .) In English it is called a message key or simply an indicator , with a slightly different meaning also called a session key .

It is in contrast to the “ day key ”, ie the partial key that is to be used constantly and uniformly for a certain period of time, usually for one day .

background

Basically, it is important that several (different) plain texts are not encrypted with identical keys. This would be a fundamental error , in cryptology as " plain text plaintext compromise " ( English Depth ) announced the unauthorized deciphering So, the " break would greatly facilitate" of Proverbs. In this regard, the cryptographically most secure solution would be to use completely different, i.e. individual, keys, similar to a one-time password or even the one-time key method ( English One Time Pad ). However, these have the serious disadvantage that the key generation as well as the administration, distribution and use of the “one-time keys” is extremely complex and is mostly not considered to be practical.

Usually, a compromise is therefore used between, on the one hand, the most uniform and thus easily distributable keys and, on the other hand, a procedure to design these in a certain way "individual" so that they are - at least partially - different. The proverb key is used for this, also known as the initialization vector (IV) for modern methods .

The saying key usually consists of a series of characters, in the simplest case a few digits or letters, with the help of which the key algorithm is "initialized", ie brought to a defined starting position. It is possible to transmit the spell key clearly (i.e. unencrypted). Since the rest of the key is secret, this does not pose a security risk. An unauthorized person can usually not use the information. In contrast, the authorized recipient naturally has the complete key documents. It is also possible to encrypt the spell key and only then transfer it. This is known as “spell key encryption”.

Examples

Individual motto keys were used in many manual and machine key procedures , especially in rotor cipher machines . Prominent examples from the Second World War are the “ Secret Writer T52 ” from Siemens & Halske , the key add-on SZ 40 and SZ 42 from Lorenz , and the Enigma with its key duplication .

The T-310/50 cipher machine used in the GDR in the 1970s and 1980s also used individual slogan keys . Here the machine itself was able to generate this with the help of a physical random number generator .

literature

Individual evidence

  1. ↑ Friedrich L. Bauer: Deciphered secrets. Methods and maxims of cryptology. 3rd, revised and expanded edition. Springer, Berlin a. a. 2000, p. 160.
  2. ^ Michael Miller: Symmetrical encryption methods. BG Teubner Stuttgart 2003, ISBN 978-3-519-02399-9 , p. 58.
  3. ↑ Tony Sale: The Bletchley Park 1944 Cryptographic Dictionary . Publication, Bletchley Park, 2001, p. 45, accessed December 14, 2018. codesandciphers.org.uk (PDF; 0.4 MB)
  4. ↑ Friedrich L. Bauer: Deciphered secrets. Methods and maxims of cryptology. 3rd, revised and expanded edition. Springer, Berlin a. a. 2000, p. 231.
  5. ↑ Bengt Beckman: Arne Beurling and Hitler's secret writer. Swedish deciphering successes in WWII. Springer, Berlin et al. 2005, ISBN 3-540-23720-8 , p. 84.
  6. ↑ Friedrich L. Bauer: Deciphered secrets. Methods and maxims of cryptology. 3rd, revised and expanded edition. Springer, Berlin a. a. 2000, p. 412.