Confusion & Diffusion

• Confusion: obscure relationship between ciphertext and plaintext. E.g. substitution

• These confusions are used in RC6:

• B=B+S[0] D=D+S[1]

• A=A+S[2r+2] C=C+S[2r+3]

• Diffusion: spreading the redundancy of the plaintext over the ciphertext. E.g. transposition(permutation)

• These diffusions are used in RC6:

• t=(B ? (2B + 1 )) <<< lg w

• u=(D ? (2D + 1)) <<< lg w

• A=((A ? t) <<< u ) + S[2i]

• C=((C ? u) <<< t) + S[2i+1]

• (A,B,C,D)=(B,C,D,A)

• the quadratic function provides fast avalanche of change between rounds.

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