Seriation (cryptology)

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Under Seriation is understood in the cryptology a method to the individual characters of a to be encrypted plaintext in a defined way in their order to rearrange . Seriation is a special case of general transposition .

example

With the manual key method of the double box key used by the German Wehrmacht between 1941 and 1944 during the Second World War , it was common to write the plain text in double lines of 21 letters each before encryption and then to encrypt the pairs of letters ( bigrams ) placed vertically one below the other . This served to strengthen the cryptographic method.

Plain text: 

DIESISTNUREINBEISPIEL TEXTUNDERDIENTHIERINU  NSERERWIKIPEDIAZURILL  USTRATIONDERSERIATION

Text written in lines of 21 characters: 

DIESISTNUREINBEISPIEL
TEXTUNDERDIENTHIERINU

NSERERWIKIPEDIAZURILL
USTRATIONDERSERIATION

Text after seriation: 

DT IE EX ST IU SN TD NE UR RD EI IE NN BT EH II SE PR II EN LU NU SS ET RR EA RT WI IO KN ID PE ER DS IE AR ZI UA RT II LO LN

The plain text converted in this way by seriation was then bigraphically encrypted and sent as ciphertext to the authorized recipient. He wrote the secret message in double lines of 21 letters each, alternating in the top and bottom lines, thus reversing the seriation. Then he used the key he knew , decrypted the ciphertext and received the original plaintext.

Seriation index

The above used in the example line length of 21 is to be regarded as freely selectable parameters, as the seriation Index ( English seriation index ) is designated. Instead of 21, a different value can of course also be selected.

literature

  • Friedrich L. Bauer : Deciphered Secrets. Methods and maxims of cryptology. 3rd, revised and expanded edition. Springer, Berlin et al. 2000, ISBN 3-540-67931-6 .
  • Charles David: A World War II German Army Field Cipher and How We Broke It . Cryptologia , Vol 20 (1), January 1996, pp 55-76.
  • Helen F. Gaines : Cryptanalysis, A Study of Ciphers and Their Solution . Courier Corporation, 1956, ISBN 0-486-20097-3 .

Web links

Individual evidence

  1. ↑ Friedrich L. Bauer: Deciphered secrets. Methods and maxims of cryptology. 3rd, revised and expanded edition. Springer, Berlin et al. 2000, p. 68.
  2. ↑ Helen F. Gaines: Cryptanalysis, A Study of Ciphers and Their Solution . Courier Corporation, 1956, ISBN 0-486-20097-3 , p. 207.