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Introduction. Conventional encryption, also referred to symmetric encryption, secret key, or single key encryption. An encryption scheme has five ingredients: Plaintext: this is the original message Encryption Algorithm: performs various transformation and substitution on the plaintext.

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Presentation Transcript
introduction
Introduction
  • Conventional encryption, also referred to symmetric encryption, secret key, or single key encryption.
  • An encryption scheme has five ingredients:
    • Plaintext: this is the original message
    • Encryption Algorithm: performs various transformation and substitution on the plaintext
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  • Secret Key: The exact substitution and transformations performs by the algorithm depends on the Key
  • Cipher Text: this is the scrambled message produced as output.
  • Decryption Algorithm: this is the encryption algorithm run in reverse
essential elements of a conventional encryption
Essential Elements of a Conventional Encryption
  • Source for a message which produces a message in plaintext.

M elements could be a 26 capital letters or nowadays the binary alphabet {0,1}

  • A key of the form:

is generated at the source and is delivered to the

destination by the mean of secure channel.

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  • The cipher text generated by this equation:
  • The intended receiver, in possession of the key is able to invert the transformation by this equation:
cryptography
Cryptography

Generally classified along three independent Dimensions:

  • The type of operations used for transforming plain text to cipher text (substitution, and transposition {permutation, and matrix})
  • The number of keys used
    • Symmetric (single key)
    • Public key or asymmetric (two keys)
  • The way in which the plaintext is processed
    • Block (cipher one block at a time)
    • Stream (cipher the input continuously)
cryptanalysis
Cryptanalysis
  • The process of attempting to discover the plain text or key is known as cryptanalysis.
  • Brute–Force approach: knowing the algorithm and cipher text and trying all possible keys.
  • Chosen Plaintext: if the opponent knows the placement of certain key words in the header of file
average time required for key exchange
Average Time Required for Key Exchange
  • An encryption scheme is computationally secure if :
    • The cost of breaking the cipher text exceeds the value of the encrypted information.
    • The time required to break the cipher exceeds the life time of the information.
classical encryption techniques
Classical Encryption Techniques

One useful classification is:

  • Substitution Technique: the letters of plaintext are replaced by other letters or by numbers, examples are (Caesar cipher and Mono-alphabetic ciphers, Hill cipher and Polyalphabetic cipher).
  • Transposition techniques: performing some permutation on the plaintext letters such as Rail Fence algorithm and rotor machines.

(go to the net and find information about them)

caesar cipher technique
Caesar Cipher Technique
  • Each letter of the alphabet is replaced by the letter stands three places further down the alphabet:
  • Note that the alphabet is wrapped around, so that the letter following Z is A
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  • Then have Caesar cipher as:
    • C = E(p) = (p + k) mod (26)
    • p = D(C) = (C – k) mod (26)
  • The important characteristics of this technique:
    • The encryption and decryption algorithms are known.
    • There are only 25 key to try which is far from security.
    • The language of the plaintext is known
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