Shamira Changeset - b52e197db5a8

Changeset - b52e197db5a8

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Laman - 7 years ago 2017-10-01 18:45:34

better exception handling

5 files changed with 36 insertions and 21 deletions:

src/cli.py

src/condensed.py

src/shamira.py

src/tests/test_condensed.py

src/tests/test_shamira.py

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src/cli.py

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 # GNU GPLv3, see LICENSE
 from argparse import ArgumentParser
 from shamira import generate, reconstruct
+from shamira import generate, reconstruct, SException
 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 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"
 	try:
 		shares=generate(args.secret,args.k,args.n,encoding)
 		for s in shares:
 			print(s)
 	except ValueError as e:
 		print("operation failed: ",e)
 	except SException as e:
 		print(e)
 def _reconstruct(args):
 	encoding=getEncoding(args)
 	try:
 		print(reconstruct(*args.share,encoding=encoding,raw=args.raw))
 	except ValueError as e:
 		print("operation failed: ",e)
 	except SException as e:
 		print(e)
 def getEncoding(args):
 	if args.hex: return "hex"
 	elif args.b32: return "b32"
 	elif args.b64: return "b64"
 	else: return ""

src/condensed.py

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@@ @@ -7,110 +7,115 @@ @@
 """Arithmetic operations on Galois Field 2**8. See https://en.wikipedia.org/wiki/Finite_field_arithmetic"""
 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 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
 	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=gfmul(prod, (gfmul(xj,inv[xj^x])))
 		res^=gfmul(y,prod)
 	return res
 ###
 import base64
 import binascii
 class SException(Exception): pass
 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):
 		points=[(x,s[i]) for (x,s) in shares]
 		res[i]=(getConstantCoef(*points))
 	return bytes(res)
 def reconstruct(*shares):
 	"""Wraps reconstructRaw.
 	:param shares: ((str) share, ...)
 	:return: (str) reconstructed secret. Too few shares returns garbage."""
 	bs=reconstructRaw(*(decode(s) for s in shares))
 	try:
 	return bs.decode(encoding="utf-8")
 	except UnicodeDecodeError:
 		raise SException('Failed to decode bytes to utf-8. Either you supplied invalid shares, or you missed the "raw" flag. Offending value: "{0}"'.format(bs))
 def decode(share):
 	try:
 		(i,_,shareStr)=share.partition(".")
 		i=int(i)
 		if not 1<=i<=255:
-			raise ValueError()
+			raise SException("Malformed share: Failed 1<=k<=255, k={0}".format(i))
 		shareBytes=base64.b32decode(shareStr)
 		return (i,shareBytes)
 	except (ValueError,binascii.Error):
-		raise ValueError('bad share format: share="{0}"'.format(share))
+		raise SException('Malformed share: share="{0}"'.format(share))
 ###
 from argparse import ArgumentParser
 def run():
 	parser=ArgumentParser()
 	subparsers=parser.add_subparsers()
 	joiner=subparsers.add_parser("join")
 	joiner.add_argument("share",nargs="+",help="shares to be joined")
 	joiner.set_defaults(func=_reconstruct)
 	parser.set_defaults(func=lambda: parser.error("missing command"))
 	args=parser.parse_args()
 	args.func(args)
 def _reconstruct(args):
 	try: print(reconstruct(*args.share))
-	except ValueError as e: print("operation failed: ",e)
+	except SException as e: print(e)
 if __name__=="__main__":
 	run()

src/shamira.py

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 # GNU GPLv3, see LICENSE
 import os
 import re
 import base64
 import binascii
 import gf256
 class SException(Exception): pass
 class InvalidParams(SException): pass
 class DetectionException(SException): pass
 class DecodingException(SException): pass
 class MalformedShare(SException): pass
 def _shareByte(secretB,k,n):
 	if not k<=n<255:
-		raise ValueError("failing k<=n<255, k={0}, n={1}".format(k,n))
+		raise InvalidParams("Failed k<=n<255, k={0}, n={1}".format(k,n))
 	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):
 		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))
 	try:
 	return bs if raw else bs.decode(encoding="utf-8")
 	except UnicodeDecodeError:
 		raise DecodingException('Failed to decode bytes to utf-8. Either you supplied invalid shares, or you missed the "raw" flag. Offending value: {0}'.format(bs))
 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(".")
 		i=int(i)
 		if not 1<=i<=255:
-			raise ValueError()
+			raise MalformedShare("Malformed share: Failed 1<=k<=255, k={0}".format(i))
 		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))
+		raise MalformedShare('Malformed share: share="{0}", encoding="{1}"'.format(share,encoding))
 def detectEncoding(shares):
 	classes=[
 		(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")
+	raise DetectionException("No expected encoding detected")
 if __name__=="__main__":
 	import cli
 	cli.run()

src/tests/test_condensed.py

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@@ @@ -25,64 +25,64 @@ class TestCondensed(TestCase): @@
 		for a in range(256):
 			for b in range(256):
 				self.assertEqual(_gfmul(a,b), gfmul(a,b))
 	def testGetConstantCoef(self):
 		self.assertEqual(getConstantCoef((1,1),(2,2),(3,3)), 0)
 		random.seed(17)
 		randomMatches=0
 		for i in range(10):
 			k=random.randint(2,255)
 			# exact
 			res=self.checkCoefsMatch(k,k)
 			self.assertEqual(res[0], res[1])
 			# overdetermined
 			res=self.checkCoefsMatch(k,256)
 			self.assertEqual(res[0], res[1])
 			# underdetermined => random
 			res=self.checkCoefsMatch(k,k-1)
 			if res[0]==res[1]:
 				randomMatches+=1
 		self.assertLess(randomMatches, 2) # with a chance (255/256)**10=0.96 there should be no match
 	def checkCoefsMatch(self,k,m):
 		coefs=[random.randint(0,255) for i in range(k)]
 		points=[(j, evaluate(coefs,j)) for j in range(1,256)]
 		random.shuffle(points)
 		return (getConstantCoef(*points[:m]), coefs[0])
 	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 secret in ["abcde","ěščřžý"]:
 			for (k,n) in [(2,3), (254,254)]:
 				with self.subTest(sec=secret,k=k,n=n):
 					shares=generate(secret,k,n)
 					random.shuffle(shares)
 					self.assertEqual(reconstruct(*shares[:k]), secret)
 					try:
 						self.assertNotEqual(reconstruct(*shares[:k-1]), secret)
-					except UnicodeDecodeError:
+					except SException:
 						pass
 		shares=generate(b"\xfeaa",2,3)
-		with self.assertRaises(UnicodeDecodeError):
+		with self.assertRaises(SException):
 			reconstruct(*shares)
 	def testDecode(self):
-		with self.assertRaises(ValueError):
+		with self.assertRaises(SException):
 			decode("AAA")
 			decode("1.")
 			decode(".AAA")
 			decode("1AAA")
 			decode("1.AAAQEAY")
 			decode("1.AAAQEAy=")
 			decode("256.AAAQEAY=")
 		self.assertEqual(decode("2.AAAQEAY="), (2,b"\x00\x01\x02\x03"))

src/tests/test_shamira.py

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 # GNU GPLv3, see LICENSE
 import random
 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(ValueError): # too few shares
+		with self.assertRaises(InvalidParams): # too few shares
 			_shareByte(b"a",5,4)
-		with self.assertRaises(ValueError): # too many shares
+		with self.assertRaises(InvalidParams): # 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):
+		with self.assertRaises(DecodingException):
 			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):
+		with self.assertRaises(MalformedShare):
 			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):
+				with self.assertRaises(DetectionException):
 					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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