[crypto] anti-kerckhoffs

[crypto] anti Kerckhoffs

Tag

SAS construction, Hidden S-box, DOI 10.1007/3-540-44987-6_24(Structural Cryptanalysis of SASAS)

Difficulty

Hard

Scenario

Field is GF(17) and plaintext size is $20$. Calculation has three layers:

1. SboxLayer1 - $S_1(x) = a_1x^2 + b_1x + c_1$ for some hidden $a_1,b_1,c_1$.
2. LinearLayer - Multiplying with hidden matrix $M$.
3. SboxLayer2 - $S_1(x) = a_2x^2 + b_2x + c_2$ for some hidden $a_2,b_2,c_2$.

TARGET is given and the goal is finding input I such that calc(I) = TARGET. A user can query at most 77777 times. When the user provides the input x, server does not replies the actual value of the output. It only replies whether each element in the output matches each element in the TARGET.