diff --git a/src/shamira/gf256.py b/src/shamira/gf256.py
--- a/src/shamira/gf256.py
+++ b/src/shamira/gf256.py
@@ -29,6 +29,7 @@ L[1] = 0
 INV = [E[255-L[i]] if i!=0 else None for i in range(256)]  # multiplicative inverse
 
 
+@cache
 def gfmul(a, b):
 	"""Fast multiplication. Basic multiplication is expensive. a*b==g**(log(a)+log(b))"""
 	assert 0<=a<=255, 0<=b<=255
@@ -38,6 +39,7 @@ def gfmul(a, b):
 	return E[t]
 
 
+@cache
 def gfpow(x, k):
 	"""Compute x**k."""
 	i = 1