Patent ID: 8681985

Claim:
A masking operation method for a symmetric key encryption system, comprising: generating, for a second Substitution-box (S-box), a masking S-box table; performing a second masking S-box operation on the second S-box by using the generated masking S-box table; and performing a first masking S-box operation on a first S-box by using the generated masking S-box table; wherein the first masking S-box operation is performed using a relation between the first S-box and the second S-box, the relation determined by the following equation s 1 ⁡ [ x ] = ⁢ A 1 ⁡ ( x - 4 ) 2 ⊕ b 1 = ⁢ A 1 ⁡ ( A 2 - 1 ⁡ ( S 2 ⁡ [ x ] ⊕ b 2 ) ) 2 ⊕ b 1 = ⁢ A 1 ⁡ ( B ⁡ ( A 2 - 1 ⁡ ( S 2 ⁡ [ x ] ⊕ b 2 ) ) ) ⊕ b 1 = ⁢ ( A 1 ⁢ BA 2 - 1 ) ⁢ S 2 ⁡ [ x ] ⊕ ( ( A 1 ⁢ BA 2 - 1 ) ⁢ b 2 ⊕ b 1 = ⁢ A 3 ⁢ S 2 ⁡ [ x ] ⊕ b 3 where s 1 [x] is the first S-box, and s 2 [x] is the second S-box.