Changeset - 90fb179128d4
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Laman - 7 years ago 2017-10-01 15:02:16

core tests and related fixes
4 files changed with 117 insertions and 9 deletions:
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src/cli.py
Show inline comments
 
@@ -4,49 +4,49 @@ from shamira import generate, reconstruc
 

	
 

	
 
def run():
 
	parser=ArgumentParser()
 
	subparsers=parser.add_subparsers()
 

	
 
	buildSplitParser(subparsers.add_parser("split"))
 
	buildJoinParser(subparsers.add_parser("join"))
 

	
 
	parser.set_defaults(func=lambda: parser.error("missing command"))
 

	
 
	args=parser.parse_args()
 
	args.func(args)
 

	
 

	
 
def buildSplitParser(parser):
 
	parser.add_argument("-k",type=int,required=True,help="number of shares necessary for recovering the secret")
 
	parser.add_argument("-n",type=int,required=True,help="number of generated shares")
 

	
 
	encoding=parser.add_mutually_exclusive_group()
 
	encoding.add_argument("--hex",action="store_true",help="encode shares' bytes as a hexadecimal string")
 
	encoding.add_argument("--b32",action="store_true",help="encode shares' bytes as a base32 string")
 
	encoding.add_argument("--b64",action="store_true",help="encode shares' bytes as a base64 string")
 

	
 
	parser.add_argument("secret",help="secret to be parser")
 
	parser.add_argument("secret",help="secret to be parsed")
 
	parser.set_defaults(func=_generate)
 
	
 

	
 
def buildJoinParser(parser):
 
	encoding=parser.add_mutually_exclusive_group()
 
	encoding.add_argument("--hex",action="store_true",help="decode shares' bytes from a hexadecimal string")
 
	encoding.add_argument("--b32",action="store_true",help="decode shares' bytes from a base32 string")
 
	encoding.add_argument("--b64",action="store_true",help="decode shares' bytes from a base64 string")
 

	
 
	parser.add_argument("-r","--raw",action="store_true",help="return secret as raw bytes")
 
	parser.add_argument("share",nargs="+",help="shares to be joined")
 
	parser.set_defaults(func=_reconstruct)
 

	
 

	
 
def _generate(args):
 
	encoding=getEncoding(args) or "b32"
 

	
 
	shares=generate(args.secret,args.k,args.n,encoding)
 
	for s in shares:
 
		print(s)
 

	
 

	
 
def _reconstruct(args):
 
	encoding=getEncoding(args)
src/gf256.py
Show inline comments
 
@@ -5,48 +5,49 @@ def _gfmul(a,b):
 
	"""Basic multiplication. Russian peasant algorithm."""
 
	res=0
 
	while a and b:
 
		if b&1: res^=a
 
		if a&0x80: a=0xff&(a<<1)^0x1b
 
		else: a<<=1
 
		b>>=1
 
	return res
 

	
 

	
 
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=_gfmul(acc, g)
 
L[1]=0
 
inv=[E[255-L[i]] if i!=0 else None for i in range(256)] # multiplicative inverse
 

	
 

	
 
def gfmul(a, b):
 
	"""Fast multiplication. Basic multiplication is expensive. a*b==g**(log(a)+log(b))"""
 
	assert 0<=a<=255, 0<=b<=255
 
	if a==0 or b==0: return 0
 
	t=L[a]+L[b]
 
	if t>255: t-=255
 
	return E[t]
 

	
 

	
 
def evaluate(coefs,x):
 
	"""Evaluate polynomial's value at x.
 

	
 
	:param coefs: [a0, a1, ...]."""
 
	res=0
 
	xK=1
 
	for a in coefs:
 
		res^=gfmul(a,xK)
 
		xK=gfmul(xK,x)
 
	return res
 

	
 

	
 
def getConstantCoef(*points):
 
	"""Compute constant polynomial coefficient given the points.
 

	
 
	See https://en.wikipedia.org/wiki/Shamir's_Secret_Sharing#Computationally_Efficient_Approach"""
 
	k=len(points)
 
	res=0
src/shamira.py
Show inline comments
 
import os
 
import re
 
import base64
 
import binascii
 

	
 
import gf256
 

	
 

	
 
def _shareByte(secretB,k,n):
 
	assert n<255
 
	assert k<=n<255
 
	coefs=[int(secretB)]+[int(b) for b in os.urandom(k-1)]
 
	points=[gf256.evaluate(coefs,i) for i in range(1,n+1)]
 
	return points
 

	
 

	
 
def generateRaw(secret,k,n):
 
	"""Splits secret into shares.
 

	
 
	:param secret: (bytes)
 
	:param k: number of shares necessary for secret recovery. 1 <= k <= n
 
	:param n: (int) number of shares generated. 1 <= n < 255
 
	:return: [(i, (bytes) share), ...]"""
 
	shares=[_shareByte(b,k,n) for b in secret]
 
	return [(i+1, bytes([s[i] for s in shares])) for i in range(n)]
 

	
 

	
 
def reconstructRaw(*shares):
 
	"""Tries to recover the secret from its shares.
 

	
 
	:param shares: ((i, (bytes) share), ...)
 
	:return: (bytes) reconstructed secret. Too few shares returns garbage."""
 
	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(*bs))
 
		points=[(x,s[i]) for (x,s) in shares]
 
		res[i]=(gf256.getConstantCoef(*points))
 
	return bytes(res)
 

	
 

	
 
def generate(secret,k,n,encoding="b32"):
 
	"""Wraps generateRaw().
 

	
 
	:param secret: (str or bytes)
 
	:param k: number of shares necessary for secret recovery
 
	:param n: number of shares generated
 
	:param encoding: {hex, b32, b64} desired output encoding. Hexadecimal, Base32 or Base64.
 
	:return: [(str) share, ...]"""
 
	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):
 
	"""Wraps reconstructRaw.
 

	
 
	:param shares: ((str) share, ...)
 
	:param encoding: {hex, b32, b64, ""} encoding of share strings. If not provided or empty, the function tries to guess it.
 
	:param raw: (bool) whether to return bytes (True) or str (False)
 
	:return: (str or bytes) reconstructed secret. Too few shares returns garbage."""
 
	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
 
	(i,bs)=share
 
	return "{0}.{1}".format(i,f(bs).decode("utf-8"))
 

	
 

	
 
def decode(share,encoding="b32"):
 
	try:
 
	(i,_,shareStr)=share.partition(".")
 
	if not shareStr:
 
		raise ValueError("bad share format")
 
	i=int(i)
 
		if not 1<=i<=255:
 
			raise ValueError()
 
	if encoding=="hex": f=base64.b16decode
 
	elif encoding=="b32": f=base64.b32decode
 
	else: f=base64.b64decode
 
	shareBytes=f(shareStr)
 
	return (i,shareBytes)
 
	except (ValueError,binascii.Error):
 
		raise ValueError('bad share format: share="{0}", encoding="{1}"'.format(share,encoding))
 

	
 

	
 
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")
 
		(re.compile(r"\d+\.([0-9A-F]{2})+"), "hex"),
 
		(re.compile(r"\d+\.([A-Z2-7]{8})*([A-Z2-7]{8}|[A-Z2-7]{2}={6}|[A-Z2-7]{4}={4}|[A-Z2-7]{5}={3}|[A-Z2-7]{7}={1})"), "b32"),
 
		(re.compile(r"\d+\.([A-Za-z0-9+/]{4})*([A-Za-z0-9+/]{4}|[A-Za-z0-9+/]{2}={2}|[A-Za-z0-9+/]{3}={1})"), "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__":
 
	import cli
 
	cli.run()
src/tests/test_shamira.py
Show inline comments
 
new file 100644
 
import os
 
import random
 
import unittest
 
from unittest import TestCase
 

	
 
from shamira import _shareByte
 
from shamira import *
 

	
 

	
 
class TestShamira(TestCase):
 
	_urandom=os.urandom
 

	
 
	@classmethod
 
	def setUpClass(cls):
 
		random.seed(17)
 
		os.urandom=lambda n: bytes(random.randint(0,255) for i in range(n))
 

	
 
	@classmethod
 
	def tearDownClass(cls):
 
		os.urandom=cls._urandom
 

	
 
	def test_shareByte(self):
 
		with self.assertRaises(AssertionError): # too few shares
 
			_shareByte(b"a",5,4)
 
		with self.assertRaises(AssertionError): # too many shares
 
			_shareByte(b"a",5,255)
 
		with self.assertRaises(ValueError): # not castable to int
 
			_shareByte("x",2,3)
 

	
 
		vals=_shareByte(ord(b"a"),2,3)
 
		points=list(zip(range(1,256), vals))
 
		self.assertEqual(gf256.getConstantCoef(*points), ord(b"a"))
 
		self.assertEqual(gf256.getConstantCoef(*points[:2]), ord(b"a"))
 
		self.assertNotEqual(gf256.getConstantCoef(*points[:1]), ord(b"a")) # underdetermined => random
 

	
 
	def testGenerateReconstructRaw(self):
 
		for (k,n) in [(2,3), (254,254)]:
 
			shares=generateRaw(b"abcd",k,n)
 
			random.shuffle(shares)
 
			self.assertEqual(reconstructRaw(*shares[:k]), b"abcd")
 
			self.assertNotEqual(reconstructRaw(*shares[:k-1]), b"abcd")
 

	
 
	def testGenerateReconstruct(self):
 
		for encoding in ["hex","b32","b64"]:
 
			for secret in [b"abcd","abcde","ěščřžý"]:
 
				for (k,n) in [(2,3), (254,254)]:
 
					raw=isinstance(secret,bytes)
 
					with self.subTest(enc=encoding,r=raw,sec=secret,k=k,n=n):
 
						shares=generate(secret,k,n,encoding)
 
						random.shuffle(shares)
 
						self.assertEqual(reconstruct(*shares[:k],encoding=encoding,raw=raw), secret)
 
						self.assertEqual(reconstruct(*shares[:k],raw=raw), secret)
 
						s=secret if raw else secret.encode("utf-8")
 
						self.assertNotEqual(reconstruct(*shares[:k-1],encoding=encoding,raw=True), s)
 
		shares=generate(b"\xfeaa",2,3)
 
		with self.assertRaises(UnicodeDecodeError):
 
			reconstruct(*shares)
 

	
 
	def testEncode(self):
 
		share=(2,b"\x00\x01\x02")
 
		for (encoding,encodedStr) in [("hex",'000102'),("b32",'AAAQE==='),("b64",'AAEC')]:
 
			with self.subTest(enc=encoding):
 
				self.assertEqual(encode(share,encoding), "2."+encodedStr)
 

	
 
	def testDecode(self):
 
		with self.assertRaises(ValueError):
 
			decode("AAA")
 
			decode("1.")
 
			decode(".AAA")
 
			decode("1AAA")
 
			decode("1.0001020f","hex")
 
			decode("1.000102030","hex")
 
			decode("1.AAAQEAY")
 
			decode("1.AAAQEAy=")
 
			decode("1.AAECAw=","b64")
 
			decode("1.AAECA?==","b64")
 
			decode("256.00010203","hex")
 
		self.assertEqual(decode("1.00010203","hex"), (1,b"\x00\x01\x02\x03"))
 
		self.assertEqual(decode("2.AAAQEAY=","b32"), (2,b"\x00\x01\x02\x03"))
 
		self.assertEqual(decode("3.AAECAw==","b64"), (3,b"\x00\x01\x02\x03"))
 

	
 

	
 
	def testDetectEncoding(self):
 
		for shares in [
 
			["1.00010f"], # bad case
 
			["1.000102030"], # bad char count
 
			["1.AAAQEAY"], # no padding
 
			["1.AAAQe==="], # bad case
 
			["1.AAECA?=="], # bad char
 
			["1.AAECAw="], # bad padding
 
			["1.000102","2.AAAQEAY="], # mixed encoding
 
			["1.000102","2.AAECAw=="],
 
			["1.AAECAw==","2.AAAQE==="],
 
			[".00010203"], # no index
 
			["00010203"] # no index
 
		]:
 
			with self.subTest(shares=shares):
 
				with self.assertRaises(ValueError):
 
					detectEncoding(shares)
 
		self.assertEqual(detectEncoding(["10.00010203"]), "hex")
 
		self.assertEqual(detectEncoding(["2.AAAQEAY="]), "b32")
 
		self.assertEqual(detectEncoding(["3.AAECAw=="]), "b64")
 
		self.assertEqual(detectEncoding(["3.AAECAwQF","1.00010203"]), "b64")
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