diff --git a/src/shamira/gf256.py b/src/shamira/gf256.py
--- a/src/shamira/gf256.py
+++ b/src/shamira/gf256.py
@@ -29,7 +29,6 @@ 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
@@ -39,6 +38,19 @@ def gfmul(a, b):
 	return E[t]
 
 
+def gfpow(x, k):
+	"""Compute x**k."""
+	i = 1
+	res = 1
+	while i <= k:
+		if k&i:
+			res = gfmul(res, x)
+		x = gfmul(x, x)
+		i <<= 1
+
+	return res
+
+
 def evaluate(coefs, x):
 	"""Evaluate polynomial's value at x.