# HG changeset patch
# User Laman
# Date 2017-09-17 22:36:32
# Node ID db65075fe7e050c401b75890228e4c8ee793754d
# Parent  438dcebc9c63518767709e1e64b6ab43c36c70ff

reconstructing the secret

diff --git a/src/gf256.py b/src/gf256.py
--- a/src/gf256.py
+++ b/src/gf256.py
@@ -35,3 +35,16 @@ def evaluate(coefs,x):
 		res^=ffmul(a,xK)
 		xK=ffmul(xK,x)
 	return res
+
+
+def getConstantCoef(k,*points):
+	res=0
+	for i in range(k):
+		(x,y)=points[i]
+		prod=1
+		for j in range(k):
+			if i==j: continue
+			(xj,yj)=points[j]
+			prod=ffmul(prod, (ffmul(xj,inv[xj^x])))
+		res^=ffmul(y,prod)
+	return res
diff --git a/src/shamira.py b/src/shamira.py
--- a/src/shamira.py
+++ b/src/shamira.py
@@ -15,4 +15,11 @@ def generate(secret,k,n):
 	return [(i+1, [s[i] for s in shares]) for i in range(n)]
 
 
-print(generate(b"key",2,3))
+def reconstruct(*shares):
+	k=len(shares)
+	secretLen=len(shares[0][1])
+	res=[None]*secretLen
+	for i in range(secretLen):
+		bs=[(x,s[i]) for (x,s) in shares]
+		res[i]=(gf256.getConstantCoef(k,*bs))
+	return bytes(res)