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Substitution Ciphers. Reference Matt Bishop, Computer Security , Addison Wesley, 2003. Substitution Ciphers (p.2). Substitution Cipher Changes characters in the plaintext to produce the ciphertext. Examples Caesar Cipher Vigenere Cipher One Time Pad. Substitution Ciphers (p.3).

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substitution ciphers
Substitution Ciphers
  • Reference
    • Matt Bishop, Computer Security, Addison Wesley, 2003.
substitution ciphers p 2
Substitution Ciphers (p.2)
  • Substitution Cipher
    • Changes characters in the plaintext to produce the ciphertext.
  • Examples
    • Caesar Cipher
    • Vigenere Cipher
    • One Time Pad
substitution ciphers p 3
Substitution Ciphers (p.3)
  • Caesar Cipher
    • Consider the plaintext to be the letters A,B,C,...,Z.
    • Now shift the sequence, say, by 3 to get D,E,F,...Z,A,B,C.
    • Then the cipher text becomes D for A, E for B, and so on.
    • If each letter is represented by integers 0,1,...,25, we can describe this process as C=(M + K) mod 26, where the key is K=3.
substitution ciphers p 4
Substitution Ciphers (p.4)
  • Vigenère Cipher
    • The Vigenère cipher chooses a sequence of keys, represented by a string.
    • Key letters are applied to successive plaintext.
    • When the end of the key sequence is reached, the key starts over again.
    • The length of the key is called the period of the cipher.
substitution ciphers p 5
Substitution Ciphers (p.5)
  • One-Time Pad
    • A variant of the Vigenère cipher.
    • The key is chosen at random.
    • The length of the key is at least as long as that of the message, and so it does not repeat.
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