# HG changeset patch
# User Laman
# Date 2017-09-23 13:00:15
# Node ID 9ccd379021d5601d3e28c5c0f71654821eb7b039
# Parent  db65075fe7e050c401b75890228e4c8ee793754d

input/output wrappers

diff --git a/src/gf256.py b/src/gf256.py
--- a/src/gf256.py
+++ b/src/gf256.py
@@ -1,4 +1,8 @@
+"""Arithmetic operations on Galois Field 2**8."""
+
+
 def _ffmul(a, b):
+	"""Basic multiplication."""
 	r=0
 	while a!=0:
 		if (a&1)!=0: r^=b
@@ -9,19 +13,20 @@ def _ffmul(a, b):
 	return r
 
 
-g=3
-E=[None]*256
-L=[None]*256
+g=3 # generator
+E=[None]*256 # exponentials
+L=[None]*256 # logarithms
 acc=1
 for i in range(256):
 	E[i]=acc
 	L[acc]=i
 	acc=_ffmul(acc, g)
 L[1]=0
-inv=[E[255-L[i]] if i!=0 else None for i in range(256)]
+inv=[E[255-L[i]] if i!=0 else None for i in range(256)] # multiplicative inverse
 
 
 def ffmul(a, b):
+	"""Fast multiplication. Basic multiplication is expensive. a*b==g**(log(a)+log(b))"""
 	if a==0 or b==0: return 0
 	t=L[a]+L[b]
 	if t>255: t-=255
@@ -29,6 +34,9 @@ def ffmul(a, b):
 
 
 def evaluate(coefs,x):
+	"""Evaluate polynomial's value at x.
+
+	:param coefs: [a0, a1, ...]."""
 	res=0
 	xK=1
 	for a in coefs:
@@ -37,7 +45,9 @@ def evaluate(coefs,x):
 	return res
 
 
-def getConstantCoef(k,*points):
+def getConstantCoef(*points):
+	"""Compute constant polynomial coefficient given the points."""
+	k=len(points)
 	res=0
 	for i in range(k):
 		(x,y)=points[i]
diff --git a/src/shamira.py b/src/shamira.py
--- a/src/shamira.py
+++ b/src/shamira.py
@@ -1,4 +1,7 @@
 import os
+import sys
+import re
+import base64
 
 import gf256
 
@@ -10,16 +13,70 @@ def shareByte(secretB,k,n):
 	return points
 
 
-def generate(secret,k,n):
+def generateRaw(secret,k,n):
 	shares=[shareByte(b,k,n) for b in secret]
-	return [(i+1, [s[i] for s in shares]) for i in range(n)]
+	return [(i+1, bytes([s[i] for s in shares])) for i in range(n)]
 
 
-def reconstruct(*shares):
-	k=len(shares)
+def reconstructRaw(*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))
+		res[i]=(gf256.getConstantCoef(*bs))
 	return bytes(res)
+
+
+def generate(secret,k,n,encoding="b32"):
+	if isinstance(secret,str):
+		secret=secret.encode("utf-8")
+	shares=generateRaw(secret,k,n)
+	return [encode(s,encoding) for s in shares]
+
+
+def reconstruct(*shares,encoding="",raw=False):
+	if not encoding:
+		encoding=detectEncoding(shares)
+
+	bs=reconstructRaw(decode(s,encoding) for s in shares)
+	return bs if raw else bs.decode(encoding="utf-8")
+
+
+def encode(share,encoding="b32"):
+	if encoding=="hex": f=base64.b16encode
+	elif encoding=="b32": f=base64.b32encode
+	else: f=base64.b64encode
+	return ["{0}.{1}".format(i,f(bs).decode("utf8")) for (i,bs) in share]
+
+
+def decode(share,encoding="b32"):
+	(i,_,shareStr)=share.partition(".")
+	if not shareStr:
+		raise ValueError("bad share format")
+	i=int(i)
+	if encoding=="hex": f=base64.b16decode
+	elif encoding=="b32": f=base64.b32decode
+	else: f=base64.b32decode
+	shareBytes=f(shareStr)
+	return (i,shareBytes)
+
+
+def detectEncoding(shares):
+	classes=[
+		(re.compile(r"\d+\.[0-9a-f]+=*"), "hex"),
+		(re.compile(r"\d+\.[A-Z2-7]+=*"), "b32"),
+		(re.compile(r"\d+\.[A-Za-z0-9+/]+=*"), "b64")
+	]
+	for (regexp, res) in classes:
+		if all(regexp.fullmatch(share) for share in shares):
+			return res
+	raise ValueError("no expected encoding detected")
+
+
+if __name__=="__main__":
+	secret=sys.argv[1].encode("utf8")
+	k=int(sys.argv[2])
+	n=int(sys.argv[3])
+	output=sys.argv[4] if len(sys.argv)>4 else "raw"
+	for share in generate(secret,k,n,output):
+		print(share)