aes::gf Namespace Reference

Helper utilities for working within a Galois Field 2**8. More...

Functions
uint8_t	mult (uint8_t a, uint8_t b)
	Multiply two bytes in GA(256)
uint8_t	inverse (uint8_t a)
	Find the Multiplicative Inverse of a byte in GF(2**8)

Detailed Description

Helper utilities for working within a Galois Field 2**8.

Function Documentation

inverse()

uint8_t aes::gf::inverse

(

uint8_t

a

)

Find the Multiplicative Inverse of a byte in GF(2**8)

Parameters

a	The value to find the inverse of.

Remarks

There are much more efficient ways to do this (Primarily just forgoing any explicit algorithm and just using a precomputed table), But for the sake of simplicity (And since there's only 256 values to check), We can just brute force it by checking against every value.

mult()

uint8_t aes::gf::mult	(	uint8_t	a,
		uint8_t	b )

Multiply two bytes in GA(256)

Parameters

a	The first byte.
b	The second byte.

Note

From https://gist.github.com/meagtan/dc1adff8d84bb895891d8fd027ec9d8c

Remarks

Most implementations would avoid this, and simply compute a 256x256 lookup table containing all values, like how SubBytes works.