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Unit 3-Symmetric Key Crypto_Part10

# Unit 3-Symmetric Key Crypto_Part10 - Unit 3 20 RC4...

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Unit 3 - 19 RC4, cont. RC4 uses an arrangement of the numbers 0 to 255 (8 bits each) in an array S which changes over time S is a self-modifying lookup table It consists of two processes A Key-based initialization Algorithm to set up the initial permutation of S based on secret key. A pseudo-random generation algorithm to Swaps elements in current lookup table Selects a keystream byte from table Note that: Each step of RC4 produces a byte, while each step of A5/1 produces only a bit

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Unformatted text preview: Unit 3 - 20 RC4 Initialization Let us denote the secret key of length N as key[i] for i = 0, 1, . .. , N −1, so that each key[i] represents one byte, and the lookup table as S[i], where each S[i] is also a byte. A Key-based initialization Algorithm appears as: for i = 0 to 255 S[ i ] = i K[ i ] = key[ i mod N ] next i j = 0 for i = 0 to 255 j = (j + S [ i ] + K [ i ] ) mod 256 swap( S [ i ], S [ j ]) next i i = j = 0...
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