Key room (cryptology)

Key space ( English key space ) is a term used in cryptography and refers to the set of all for encryption methods possible keys . The size of the key space quantifies the number of all keys and is also referred to as the number of keys. A logarithmic measure of the size of the key space is the key length , which is specified in bits .

Size of the key space

A sufficient size of the key space is an important and necessary condition for the security of a cryptographic method. However, it alone does not offer sufficient protection against unauthorized deciphering ( cracking ). With cryptographically weak encryption methods, an attacker may succeed in discovering abbreviations that enable him to find the key without having to try out all possible keys. An example of this is the pattern search as a cryptanalytic attack method on ciphertexts encrypted by monoalphabetic substitution . Although here the key space for a secret alphabet with, for example, 26 characters (corresponding to the 26 capital letters of the usual Latin alphabet ) 26! ( Factorial ) is, which is about 4 x 10 ²⁶ possible keys that succeeds deciphering of such encrypted text with relative ease and without any exhaustive search ( Exhaustion ).

Other meanings

A distinction must be linguistically set of all possible keys and a key area in the picture, the soldiers of the Secret Service radio detection of between explicitly in the text key space OKW when encrypting or decrypting messages using the key machine Enigma shows

• This meaning of the term should not be confused with a key space  (image) (also: encryption space ; rarely: Chiffrierzimmer ) in which messages comparable or decrypted are in cryptology - jargon in general terms "So prorated be".

• There is also key room as a name for a room in which keys are stored, for example on key boards .

• Key space (also: key zone ) is used with a different meaning in geography , spatial planning or military strategy . There one designates a zone or a geographical area to which a key function, for example for industrial or urban development or for spatial defense , is assigned.

literature

• Friedrich L. Bauer : Deciphered Secrets. Methods and maxims of cryptology. 3rd, revised and expanded edition. Springer, Berlin a. a. 2000, ISBN 3-540-67931-6 .

Web links

• Peter Hellekalek: Lecture on cryptology. University of Salzburg , 2014, PDF; 675 kB accessed on November 15, 2018.
• Alfred J. Menezes, Paul C. van Oorschot, and Scott A. Vanstone: Handbook of Applied Cryptography. CRC Press, ISBN 0-8493-8523-7 , PDF; 480 kB accessed on November 15, 2018.

Individual evidence

1. ^ Alfred J. Menezes, Paul C. van Oorschot and Scott A. Vanstone: Handbook of Applied Cryptography . CRC Press, ISBN 0-8493-8523-7 , pp. 224 .
2. ↑ Peter Hellekalek: Lecture cryptology. University of Salzburg, 2014, p. 8 ff.
3. ↑ Friedrich L. Bauer: Deciphered secrets. Methods and maxims of cryptology. 3rd, revised and expanded edition. Springer, Berlin a. a. 2000, p. 184. ISBN 3-540-67931-6 .
4. ↑ Tür und Tor article in Zeit Online from April 3, 1987, accessed on November 15, 2018.