Changeset - 3907396d80a5
[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:
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]
0 comments (0 inline, 0 general)