Chaocipher

Chaocipher is the name for a symmetric encryption method, which was developed in 1918 by John Francis Byrne. Byrne held the algorithm does not break. Until his death, Byrne tried unsuccessfully to convince government authorities of his trial because he did not have the intention to make available to the public details of the algorithm. In 2010, his family donated the posthumous papers of the inventor at the National Cryptologic Museum in Ft. Meade, USA, whereby the algorithm was first made ​​public.

Operation

In its original form, Byrne had his procedure planned as a mechanical device, but never built it. ( A version made ​​of wood and cardboard was made by his son. )

The device consists of two adjacent slices, on the circumference are each the 26 letters of the alphabet in varying sequence. The disks are rotatably mounted and connected to each other, that the other disc rotates in opposite directions upon rotation of a wheel in a direction (clockwise or counterclockwise).

The principle of Chaocipher is that both alphabets are permuted after each encryption or decryption of a letter. Since this permutation depends on the previously encrypted or decrypted letters, it is in this process is a self-synchronizing stream cipher.

Overview

Although the use of Chaocipher was intended as a machine, the principle can be traced with each other standing alphabets for plaintext and ciphertext. Here, the upper alphabet for the left wheel is ( the ciphertext GT), and the lower alphabet for the right pane ( the plaintext KT). The following diagram shows a possible initial state for the algorithm, the letters are arranged in two rows / disks is the key dar.

* Links (GT ): HXUCZVAMDSLKPEFJRIGTWOBNYQ Law ( KT): PTLNBQDEOYSFAVZKGJRIHWXUMC --------------------------------------- Position: 11111111112222222               12345678901234567890123456 Note the symbols and *, which denotes Byrne zenith and nadir. You are looking at two alphabets at position 1 and 14

At the beginning of the left and right alphabet are aligned at their respective zenith markers. The encryption of a plaintext letter is then carried out in three steps. ( These steps are repeated until all the letters of the plaintext are encrypted. )

To find the corresponding ciphertext letters, one seeks the letter of the plaintext alphabet in the right. The standing directly above letter of the alphabet left is the corresponding letter in the ciphertext. Encrypts one in this example, the letter A, we obtain the ciphertext letter P ( see arrow).

↓ * Links (GT ): HXUCZVAMDSLKPEFJRIGTWOBNYQ Law ( KT): PTLNBQDEOYSFAVZKGJRIHWXUMC --------------------------------------- Position: 11111111112222222               12345678901234567890123456 Permutation of the ciphertext alphabet

The permutation is done in four steps:

Starting from the initial state shown above, see these steps as follows: First, the alphabet is shifted to the newly found ciphertext letter P is in position 1 ( Zenith ).

* Links (GT ): PEFJRIGTWOBNYQHXUCZVAMDSLK Thereafter, the point is 1 (S) taken at the zenith position.

* Links (GT ): P.FJRIGTWOBNYQHXUCZVAMDSLK In the third step, the letter from Zenith 2 ( F) to nadir ( Q) are shifted one position to the left.

* Links (GT ): PFJRIGTWOBNYQ.HXUCZVAMDSLK Finally, the extracted letter ( E) inserted at position Nadir again.

* Links (GT ): PFJRIGTWOBNYQEHXUCZVAMDSLK Permutation of the plaintext alphabet

The plaintext alphabet is similar permutes the ciphertext alphabet in five steps:

For the example given the right alphabet looks after Step 1 is as follows:

* Law ( KT): AVZKGJRIHWXUMCPTLNBQDEOYSF Now moving to another location is to the left.

* Law ( KT): VZKGJRIHWXUMCPTLNBQDEOYSFA Next, the point at the zenith position 2 ( K) is removed.

* Law ( KT): VZ.GJRIHWXUMCPTLNBQDEOYSFA In the fourth step, the letter from Zenith 3 ( G) to nadir (P) shifted one position to the left.

* Law ( KT): VZGJRIHWXUMCP.TLNBQDEOYSFA Finally, the extracted letter (K) is re-inserted.

* Law ( KT): VZGJRIHWXUMCPKTLNBQDEOYSFA After these two permutations of the next letter of the plaintext to be encrypted. If the next letter is an N, as would the corresponding ciphertext U loud.

* ↓ Links (GT ): PFJRIGTWOBNYQEHXUCZVAMDSLK Law ( KT): VZGJRIHWXUMCPKTLNBQDEOYSFA decode

The procedure for decrypting a ciphertext using Chaocipher is almost identical to that when encrypting. Based on the same initial state of the two alphabets is the difference only in that one instead of the plaintext letter in the alphabet right now looking for the ciphertext letter in the alphabet and so left the attendant plaintext letters. Then takes you to permute the steps above to two alphabets, and can then find the next ciphertext letter and the corresponding plaintext letter.