O'Reilly logo

Computer Security and Cryptography by Alan G. Konheim

Stay ahead with the world's most comprehensive technology and business learning platform.

With Safari, you learn the way you learn best. Get unlimited access to videos, live online training, learning paths, books, tutorials, and more.

Start Free Trial

No credit card required

7.10 CRIBBING PURPLE: FINDING THE C-STEPPERS

Recovery of the C-steppers is considerably more complicated, because the consonant substitution has the very large period of 253. Rowlett [1998, p. 151] describes the excitement when Genevieve Feinstein (née Grotjan) discovered the characteristic property of the C-stepper alphabets that was crucial in the success of Magic, the United States codename for intelligence derived from the cryptanalysis of PURPLE.

Table 7.52 lists the positions of the three banks of C-steppers for 0 ≤ i < 78.

7.10.1 First Characteristic Property of C-Steppers

If

  • The speed of the C-stepper banks is (S, M, F).
  • The permutations Π (i, i + 1) (i = 0, 1) are factored into the C-stepper substitutions, and
  • The initial positions of the V-stepper and all C-steppers are 0, then

the ciphertext alphabets in positions [0, 23] and [26, 49] are related as follows:

image

Table 7.52 shows

image

image

If x2, x2 CON and

image

implies

image

for 0 ≤ i ≤ 23. That is, when

  • the consonant x1 is enciphered in position ...

With Safari, you learn the way you learn best. Get unlimited access to videos, live online training, learning paths, books, interactive tutorials, and more.

Start Free Trial

No credit card required