Computer Security and Cryptography

9.20 A CLASS OF BLOCK CIPHERS

A “Cryptographic Device” designed by my former colleague Dr. Roy L. Adler is described in IBM [1974] and in U.S. Patent #4.255,811 “Key Control Block Cipher System”, issued to Adler on March 10, 1981. This algorithm provides the cryptographic feature in a key-card entry system to be described in Chapter 18.

128-bit plaintext blocks are enciphered to 128-bit ciphertext blocks under, the control of a 128-bit key:

Like LUCIFER and DES, encipherment is the result of r rounds; the (3 × 128) + 7 bits of key used in a round are derived from the user-supplied 128-bit key in a manner to be described shortly.

First, a 128-bit key a₀ = (a_0,0, a_0,1, …, a_0,127) derived by the key processor from the user-supplied key is added modulo 2¹²⁸ to the 128-bit plaintext block x = (x₀, x₁, …, x₁₂₇):

Using the key supplied by the processing device, the steps in the ith round are:

Ri-1 Modulo 2¹²⁸-addition of 128-bit key bi = (b_i,0, b_i,1, …, b_i,127)

Ri-2 128-to-128 wire-crossing θ = (θ₀, θ₁, …, θ₁₂₇)

Ri-3 7- or 8-bit shift-left-circular ρ_i determined by key β_i = (β_i,0, β_i,1, …, ...