L04-Ciphers-Substitution

L04-Ciphers-Substitution - Classical Cryptography 1 Ciphers...

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1 Classical Cryptography Classical Cryptography
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2 Ciphers Ciphers Transforming intelligible text into unintelligible text – Simple ciphers –B lock
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3 Techniques Techniques • Substitution – permutations on texts •T r a n s p o s i t i o n – permutations on places
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4 Symmetric Symmetric - - key Encryption and Decryption key Encryption and Decryption • Symmetric Key algorithms use a secret key for Encryption and Decryption. – transformations are simple and fast enough for practical use and implementation. – “Keyspace” large enough to protect against exhaustive search. Key (k) Ciphertext (C) Encrypt E k (P) Plaintext (P) Key (k) Plaintext (P) Decrypt D k (P) Ciphertext (C)
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5 Substitution Methods Substitution Methods – Mono-Alphabetic Ciphers • Caesar/shift – Poly-Graphic Ciphers • Playfair Cipher (keyed-table lookup) • Hill Cipher (matrix-multiplication operation) – Poly-Alphabetic Ciphers • Vigenere Cipher
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6 Simple Substitution Simple Substitution
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L04-Ciphers-Substitution - Classical Cryptography 1 Ciphers...

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