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core: add OpSecp256k1Commitment
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apoelstra committed May 17, 2017
1 parent 21937db commit 5a21625
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Showing 3 changed files with 32 additions and 1 deletion.
3 changes: 3 additions & 0 deletions opentimestamps/core/op.py
Original file line number Diff line number Diff line change
Expand Up @@ -347,3 +347,6 @@ def _do_op_call(self, msg):
r = sha3.keccak_256(bytes(msg)).digest()
assert len(r) == self.DIGEST_LENGTH
return r

from opentimestamps.core.secp256k1 import OpSecp256k1Commitment

21 changes: 21 additions & 0 deletions opentimestamps/core/secp256k1.py
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Expand Up @@ -9,6 +9,27 @@
# modified, propagated, or distributed except according to the terms contained
# in the LICENSE file.

import hashlib

from opentimestamps.core.op import BinaryOp, MsgValueError

@BinaryOp._register_op
class OpSecp256k1Commitment(BinaryOp):
"""Execute the map commit -> [P + sha256(P||commit)G]_x for a given secp256k1 point P"""
TAG = b'\x09'
TAG_NAME = 'secp256k1commitment'

def _do_op_call(self, msg):
hasher = hashlib.sha256()
pt = Point.decode(self[0])
hasher.update(pt.encode())
hasher.update(msg)
tweak = int.from_bytes(hasher.digest(), 'big')
tweak_pt = SECP256K1_GEN.scalar_mul(tweak)
final_pt = pt.add(tweak_pt)
return final_pt.x.to_bytes(32, 'big')


## What follows is a lot of inefficient but explicit secp256k1 math
class Point(object):
inf = True
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9 changes: 8 additions & 1 deletion opentimestamps/tests/core/test_secp256k1.py
Original file line number Diff line number Diff line change
Expand Up @@ -9,6 +9,7 @@
# modified, propagated, or distributed except according to the terms contained
# in the LICENSE file.

import hashlib
import binascii
import unittest

Expand All @@ -20,7 +21,7 @@ def test_point_rt(self):
gen = SECP256K1_GEN
encode = gen.encode()
self.assertEqual(encode, binascii.unhexlify("0279be667ef9dcbbac55a06295ce870b07029bfcdb2dce28d959f2815b16f81798"))
gen2 = Point().decode(encode)
gen2 = Point.decode(encode)
self.assertEqual(gen, gen2)

def test_pinv(self):
Expand Down Expand Up @@ -99,3 +100,9 @@ def test_scalar_mul(self):
self.assertEqual(p2.scalar_mul(-1), np2)
self.assertEqual(p1.scalar_mul(3), p3)

def test_op_signtocontract(self):
pt_encode = binascii.unhexlify("0308aec434612f56df3f02c4e678260424415882ebd3efc16d52e3f9c1e39afdb0")
msg = hashlib.sha256("This is andytoshi on 2017-05-16 21:30 UTC".encode()).digest()
result = binascii.unhexlify("d386ef692770fcecad43362cf541858662e4ebe31d3ad04d196f94168897947a")
self.assertEqual(OpSecp256k1Commitment(pt_encode)(msg), result)

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