Lign 17 midterm study guide.pdf

No matter what n is applying the cipher 26 times will

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the alphabet, it will eventually always recover the plaintext. - No matter what N is, applying the cipher 26 times will always recover the plaintext again. Kerckoff’s Principle- Monoalphabetic substitution cipher with key phrase. Security depends only on keeping the key secret - Key phrase= secret code - A b c d e f g h i j k l m n o p q r s t u v w x y z = S e c r t o d f g h i j k l m n p q uvw x y z a b - Can be broken using frequency analysis

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6. Ways to make frequency analysis more difficult: --irregular spelling I.e. lts mt nxt two megl hll--->lets meet next to mgill hall --addition of ‘nulls’: symbols in cipher text that corresponds to nothing in plain text. --addition of “dowbleths”: letter doublers Code : symbols stand for whole word Nomenclator : combo of cipher plus code Key: A=Z, E=3, F=U, H=B, I=1, L=N, T=D 9=the If all the ===== 1u 6zn4c 9 7. Monoalphabetic substitution cipher with homophones- Multiple numbers assigned to one letter based on the letter’s frequency. 8. Types of mappings- One-to-one : (e.g. MSCs, caesar shift) - Each symbol in the plain alphabet maps to a single symbol in the cipher alphabet. - Each symbol in the cipher alphabet maps to a single symbol in the plain alphabet.
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• Winter '08
• Kehler
• Cryptography, Substitution cipher, Rail Fence Cipher

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