Shamira Changeset - 3907396d80a5

Changeset - 3907396d80a5

Parent rev.

Child rev.

[Not reviewed]

default

0 1 0

Laman - 7 years ago 2017-09-23 13:22:27

documentation

1 file changed with 25 insertions and 2 deletions:

src/shamira.py

0 comments (0 inline, 0 general)

src/shamira.py

➞

Show inline comments

 import os
 import sys
 import re
 import base64
 import gf256
-def shareByte(secretB,k,n):
+def _shareByte(secretB,k,n):
 	assert 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):
 	shares=[shareByte(b,k,n) for b in secret]
 	"""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))
 	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
 	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)

0 comments (0 inline, 0 general)