Computer Security and Cryptography

11.5 KNAPSACK ENCIPHERMENT AND DECIPHERMENT OF ASCII-PLAINTEXT

Knapsack encipherment derives a μ-bit ciphertext integer B⁽ⁱ⁾ from each plaintext (0,1}-vector Then Internet standard [Linn, 1989] specifies the translation from ASCII text for Merkle–Hellman encipherment. I use a similar coding translation scheme illustrated in Example 11.11, which follows.

11.5.1 Knapsack Encipherment of ASCII-Plaintext

Plaintext: x⁽⁰⁾ x⁽¹⁾ … x^(N−1) (ASCII characters)

Kuapsack Public Parameter. a = (a₀, a₁, …, a_n−1)

Ciphertext. y = (y⁽⁰⁾, y⁽¹⁾, …, y^{(M − 1)})

-vectors.

E1. Each of the N ASCII plaintext characters x⁽ⁱ⁾ in first coded into the 7-bit binary representation of its ordinal position in the ASCII character set

E2. The vectors {x⁽ⁱ⁾} are concatenated to form the binary plaintext

E3. The binary plaintext z is divided into equal length blocks of n bits, padding z on the right by 0's if necessary. By this process blocks of n bits are obtained

E4. For each bit-vector (z⁽ⁱ⁾), the integer is computed; ...