Lecture01 - time required to break exceeds lifetime of the...

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I. Symmetric Cipher Model A. Terms: Plaintext, Encryption Algorithm, Secret key, ciphertext, and decryption algorithm (in the symmetric model, this is the encryption algorithm run in reverse.) Should be secure even if the algorithm is known. Symmetric vs. Asymmetric B. Characterization of Crypto systems 1. Type of operation used in transforming the plaintext into ciphertext 2. The number of keys used. 3. The way in which the plaintext is processed. C. Cryptanalysis 1. Try to reduce the number of possible keys you have to try using information about the algorithm. 2. Try all keys. 3. Types of attacks: Ciphertext only, Known plaintext, Chosen plaintext, Chosen ciphertext. Unconditional security: There isn't enough information to break it. (One-time pad) We will aim for: cost of breaking exceeds cost of information,

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Unformatted text preview: time required to break exceeds lifetime of the information D. Caeser Cipher 1. C = E(p,k) = (p+k) mod 26 E. Affine Cipher 1. C = E(p, a, b) = (ap+b) mod 26 No detail about what a's and b's are permissible today. F. Substitution Cipher Substitute any one letter for another! Frequency Analysis can be used to break it. 1. Look for most frequent letters 2. Look for common digrams and trigrams, and other repeated sections of ciphertext. G. Playfair 5x5 grid Fill in key word and double I/J. 1. Repeated plaintext letters in a pair filled with an X or another filler. 2. Same row -> each letter to the right in the row. 3. Same column -> each letter below 4. letter in the SAME row, and the column of the other letter....
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Lecture01 - time required to break exceeds lifetime of the...

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