Let’s discuss Beatboxer
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Given that the S-Box is linear, the cipher in the challenge is an affine function because the S-Box is the non-linear part
Given that the S-Box is linear, the cipher in the challenge is an affine function because the S-Box is the non-linear part.
So, AES(x) = A*x + B
, where A is a 16x16 matrix and B is a 16x1 vector. We can find A and B by solving the system of equations. Note that the plus sign represents the XOR operation because the field is GF(2). A depends on the S-Box and B depends on the key.
The challenge provides only one attempt to encrypt a plaintext of our choice.
We can use the fact that AES(0) = 0 to find B and then it’s easy to compute A locally.
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