3 ms·
GF(2^n) Galois Field numbers are actually somewhat inefficient at multiplication. At least, in the 90s when AES was invented (today we have pmull and carryless-
by dragontamer 3y ago
GF(2^n) Galois Field numbers are actually somewhat inefficient at multiplication. At least, in the 90s when AES was invented (today we have pmull and carryless-multiplication that speeds things up, but its still overall slow compared to normal multiplication).
Because of this, modern ciphers prefer Add-Xor-Rotate ciphers instead of Galois Field operations. As it turns out, Add-Xor-Rotate groups are provably invertible too, and are far, far more efficient to run than Galois Field operations.
- adrian_b 3y agoFast Galois Field operations are significantly cheaper to implement in hardware. The only reason why they may be slower in software is because the Intel and AMD CPUs already had fast integer operations, but neither Intel nor AMD have bothered to also provide a fast implementation of carry-less multiplication on most of their CPU models (though on most recent models the speed is adequate for polynomial authentication done concurrently with AES encryption).