Fundamentals of Information Encryption - Multilevel Security for Relational Databases - page 80

A B C D

- -

S[2r+2] S[2r+3]

-

-

S[2i] S[2i+1]

>>>

>>>

<<< f <<< f

lg w lg w

- S[0] - S[1]

A B C D

Figure 4.8 Decryption with RC6 w/r/b .

Output: Four w -bit plaintext values are stored in registers A, B,
C, and D.
Procedure:

C = C − S [2r + 3];

A = A − S [2r + 2];

for i = r downto 1 do

{(A, B, C, D) = (D, A, B, C);

u = (D × (2D + 1)) <<< lg w;

t = (B × (2B + 1)) <<< lg w;

C = ((C − S[2i + 1]) >>> t) ⊕ u;

A = ((A − S[2i]) >>> u) ⊕ t;}

End

D = D − S [1];

B = B − S [0];