Advanced Encryption Standard-Computer Network Security-Lecture Slides, Slides of Computer Security

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Computer Network SecurityLecture 4Advanced Encryption Standard& Cipher Block Chaining

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Advanced Encryption Standard"It seems very simple.""It is very simple. But if you don't know what thekey is it's virtually indecipherable." —Talking to Strange Men, Ruth Rendell

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AES History  After testing and evaluation, shortlist in Aug-99:  MARS (IBM) - complex, fast, high security margin  RC6 (USA) - v. simple, v. fast, low security margin  Rijndael (Belgium) - clean, fast, good security margin  Serpent (Euro) - slow, clean, v. high security margin  Twofish (USA) - complex, v. fast, high security margin  NIST published a final standard (FIPS PUB 197)in Nov. 2001.  NIST selected Rijndael^ as^ the^ proposed

AES

algorithm.  The^ two^ researchers^

from^ Belgium^ were:^ Dr.

Joan Daemen and Dr.Vincent Rijmen.

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AES Requirements  Private key symmetric block cipher  128-bit data, 128/192/256-bit keys  Stronger & faster than Triple-DES  Provides full specification & design details  Both C & Java implementations  NIST have released all submissions &unclassified analyses

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^ Data block of 4 columns of 4 bytes ^ This^ block^ is^ copied

into^ State^ array,^ which

is

modified at each stage of encryption or decryption.  After the final stage, State is copied to an output.  Key is expanded to array of words  Has 9/11/13 rounds in which state undergoes:^ ^ byte substitution (1 S-box used on every byte)^ ^ shift rows (permute bytes between groups/columns)^ ^ mix^ columns^ (substitution

using^ matrix^ multipy^ of

Rijndael Cipher groups)  add round key (XOR state with key material)  view as alternating XOR key & scramble data bytes  With fast XOR & table lookup implementation

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Rijndael Cipher

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Rijndael Cipher

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Rijndael Cipher

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Rijndael Cipher

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Rijndael Cipher

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Rijndael Cipher

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Rijndael Cipher

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Rijndael Cipher

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Rijndael Cipher