# Tag Info

6

You should think of Rijndael's S-box as a function that maps bytes to bytes, where a byte (octet) is considered to be a member of a finite field of size $2^8$ (with xor as addition). It's not seen as a 16x16 octet array, really. The substitution is then just done byte-wise: every octet in the 4x4 block is replaced by its function value under the S-box ...

4

Well, for one thing, you are not using a "One Time Pad". A "One Time Pad" means, by definition, that someone generates a pad of numbers using true randomness (and not algorithmicly), and that no potential adversary has any information on what that pad may contain. Then, that pad is given to both the sender and the receiver, and then the sender uses it to ...

3

Item 2 has been answered satisfactorily, so this will focus on point 1: the s-box. The size of the s-box is not a 16x16 array unless it is viewed as such. The s-box is actually an 8-bit non linear transformation of the input, and is only viewed as a 16x16 array if you arrange it as a table of such dimensions. This array would then be a 1 to 1 representation ...

3

standard AES disclaimer: Given the questions you've asked, you should not implement AES yourself in a real-world system because there are lots of security considerations when implementing ciphers. Think of the S-box as a function from byte $\to$ byte. So, to look up the image of $x$ under the s-box transformation, you simply use $S_\text{box}(x)$, which ...

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