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The stream cipher described in Definition 2.1.1 can easily be generalized to work in alphabets other than the binary one. For manual encryption, an especially useful one is a stream cipher that operates on letters. 1. Develop a scheme which operates with the letters A, B,..., Z, represented by the numbers 0,1,...,25. What does the key (stream) look like? What are the encryption and decryption functions? 2. Decrypt the following cipher text: bsaspp kkuosp

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temmydbrain

Answer:

Check the explanation

Explanation:

1) supposing the keystream is a stream that is of random bits in Z26, we can describe a stream cipher based on the Latin Alphabet that is as follows (where A ↔ 0, B ↔ 1, C ↔ 2 etc):

[tex]y_{i} =x_{i} +k_{i}[/tex] mod26

[tex]x_{i} =y_{i} -k_{i}[/tex] mod26

2)

[tex]x_{i} =y_{i} -k_{i}[/tex] = ” B ” − ” R ” = 1 − 17 = − 16 ≡ 10 mod 26 = ” K ” etc ·

The Decrypted Text is: ”KASPAR HAUSER”

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