return s, statesToIndices[h]
def findSecondPreimage(m, hashFn, iv, blockLength, hashLength):
blockCount = (len(m) + blockLength - 1) // blockLength
k = blockCount.bit_length()
prefixState, blocks = makeExpandablePrefix(hashFn, iv, blockLength, k)
intermediateStateIter = getIntermediateStates(m, hashFn, iv, blockLength)
bridge, collisionBlockCount = findIntermediateStateCollision(
hashFn, prefixState, blockLength, hashLength, intermediateStateIter, k)
m2 = makeExpandedPrefix(blockLength, blocks, k,
collisionBlockCount) + bridge
m2 += m[len(m2):]
return m2
if __name__ == '__main__':
m = get_random_bytes(100)
h = challenge52.badHash(m, b'')
m2 = findSecondPreimage(m, challenge52.badHash, b'',
challenge52.badHashBlockLength,
challenge52.badHashHashLength)
h2 = challenge52.badHash(m2, b'')
print(m, m2, h, h2)
if len(m2) != len(m):
raise Exception('{0} != {1}'.format(len(m2), len(m)))
if h2 != h:
raise Exception(h2 + b' != ' + h)
i += 1
if not statesToIndices:
raise Exception('unexpected')
s, h = findCollisionInSet(hashFn, iv, blockLength, statesToIndices)
return s, statesToIndices[h]
def findSecondPreimage(m, hashFn, iv, blockLength, hashLength):
blockCount = (len(m) + blockLength - 1) // blockLength
k = blockCount.bit_length()
prefixState, blocks = makeExpandablePrefix(hashFn, iv, blockLength, k)
intermediateStateIter = getIntermediateStates(m, hashFn, iv, blockLength)
bridge, collisionBlockCount = findIntermediateStateCollision(hashFn, prefixState, blockLength, hashLength, intermediateStateIter, k)
m2 = makeExpandedPrefix(blockLength, blocks, k, collisionBlockCount) + bridge
m2 += m[len(m2):]
return m2
if __name__ == '__main__':
m = util.randbytes(100)
h = challenge52.badHash(m, b'')
m2 = findSecondPreimage(m, challenge52.badHash, b'', challenge52.badHashBlockLength, challenge52.badHashHashLength)
h2 = challenge52.badHash(m2, b'')
print(m, m2, h, h2)
if len(m2) != len(m):
raise Exception('{0} != {1}'.format(len(m2), len(m)))
if h2 != h:
raise Exception(h2 + b' != ' + h)
totalBlockLength += k + 1
totalLength = totalBlockLength * blockLength
return hashFn(padFn(b'', totalLength), collisionTree[-1][0][0], pad=False)
def forgePrediction(hashFn, iv, padFn, initialStateMap, collisionTree, messageLength, blockLength, m):
if len(m) > messageLength:
raise Exception('message too big')
paddedMessageLength = messageLength + (-messageLength % blockLength)
m += b'\x00' * (paddedMessageLength - len(m))
h = hashFn(m, iv, pad=False)
glue, h = challenge53.findCollisionInSet(hashFn, h, blockLength, initialStateMap)
m += glue
suffix = getSuffixFromCollisionTree(initialStateMap, collisionTree, h)
m += suffix
return m
if __name__ == '__main__':
k = 5
messageLength = 100
(initialStateMap, collisionTree) = constructCollisionTree(challenge52.badHash, challenge52.badHashBlockLength, challenge52.badHashHashLength, k)
prediction = generatePrediction(challenge52.badHash, challenge52.badHashPadMessage, initialStateMap, collisionTree, messageLength, challenge52.badHashBlockLength)
print('Prediction', prediction)
forgedPrediction = b'Dodgers win the World Series!!'
forgedPredictionMessage = forgePrediction(challenge52.badHash, b'', challenge52.badHashPadMessage, initialStateMap, collisionTree, messageLength, challenge52.badHashBlockLength, forgedPrediction)
h = challenge52.badHash(forgedPredictionMessage, b'')
print('Forged prediction', forgedPredictionMessage, h)
