Blind signature support in pyelliptic #1509

PeterSurda · 2019-08-26T15:50:55Z

add blind signature functionality to pyelliptic as described in Blind signatures as an alternate proof a message is not spam #1409
add tests for blind signatures
PEP8 fixes for pyelliptic
some minor refactoring is necessary for further integration, this is just a
minimal implementation to pass a test

PeterSurda · 2019-08-26T16:06:18Z

I'll fix the pylint complaints.

g1itch

Honestly, I don't understand what exactly is going on here, but your test case may be better.

g1itch · 2019-08-27T09:09:52Z

src/tests/test_blindsig.py

@@ -0,0 +1,27 @@
+#!/usr/bin/env python


Shebang is not needed here.

g1itch · 2019-08-27T09:15:09Z

src/tests/test_blindsig.py

+import os
+import unittest
+
+from src.pyelliptic.eccblind import ECCBlind


from pybitmessage.pyelliptic.eccblind import ECCBlind

This breaks the test.

It depends on how you run it.

Travis CI should be OK, because I used such imports before: https://github.com/Bitmessage/PyBitmessage/blob/v0.6/src/tests/test_config.py#L8

g1itch · 2019-08-27T09:16:07Z

src/tests/test_blindsig.py

+        blind_sig.create_signing_request(msg)
+        blind_sig.blind_sign()
+        blind_sig.unblind()
+        assert blind_sig.verify()


self.assertTrue(blind_sig.verify())

g1itch · 2019-08-27T09:19:42Z

src/tests/test_blindsig.py

+    @staticmethod
+    def test_blind_sig():
+        """
+        Perform a test of full sequence using a random certifier's key and a


If you write docstring in one line it will be shown in the test results. e.g.

def test_blind_sig(self): """Test full sequence using a random certifier key and a random msg"""

PeterSurda · 2019-08-27T10:16:51Z

@g1itch I'll make the changes you requested.

The low level math I also don't understand, but it looks like it does what the paper says. On a high level, the paper mentions 5 steps (in Section 4), these are roughly mapped to 6 high level methods in the ECCBlind class, with some reshuffling because some are executed by the signer and some by the requester. It needs to be refactored, because the signer and requester need to communicate and pass data, so there will be one object at the signer's side and one at the requester's side, but here I just reuse a single object. Also in __init__, it now generates a new pubkey, wereas for actual deployment the pubkey will be loaded from the disk (like a CA for traditional PKI). There still are open questions about how to serialise the data. This all will be solved in the subsequent PRs.

g1itch · 2019-08-27T10:33:19Z

I also expected to find the blinded message and its signature and check the signature's validity.

PeterSurda · 2019-08-27T11:02:47Z

@g1itch The message is only blinded internally and such blinded message is only available to the requester, it's not made public. Similarly with the blinded signature, that's calculated by the signer and then transmitted to the requester and unblinded by him.

What you see publicly is the message (in the case of PyBitmessage's wire protocol, this will be the object data), the signature (which has two components, s and F), and pubkey of the signer (Q). There is also r, but that's derived from F. F is a point on a finite field and r is its x coordinate modulo n, although it looks to me like the current code skips the modulo n, the way I understand the code is that n is selected from the elliptic curve used, so x can't higher than that. But I don't really understand ECC so I may be wrong.

Then during the verification, you take the signature, the signer's pubkey and the message, and if verification succeeds, it means the singer signed the message, just like with traditional PKI, except here the signer doesn't know which of the requests he signed correspond to which message..

g1itch · 2019-08-27T11:20:29Z

src/pyelliptic/eccblind.py

+        """
+        Generate an ECC keypair
+        """
+        d = ECCBlind.ec_get_random(group, ctx)


d = self.ec_get_random(group, ctx) ?

pylint/flake8 complained.

because of @staticmethod. well, maybe this really should be a static method

g1itch · 2019-08-27T12:35:54Z

I am trying to split signer and requester with no luck ):

    def test_blind_sig(self):
        """Test full sequence using a random certifier key and a random msg"""
        signer_obj = ECCBlind()
        signer_obj.signer_init()
        signer_obj.create_signing_request('dummy')

        requester_obj = ECCBlind()
        requester_obj.R = signer_obj.R
        requester_obj.keypair = (0, signer_obj.keypair[1])

        msg = os.urandom(64)
        requester_obj.create_signing_request(msg)

        signer_obj.m_ = requester_obj.m_
        signer_obj.blind_sign()

        requester_obj.s_ = signer_obj.s_
        requester_obj.unblind()

        signer_obj.m = requester_obj.m
        signer_obj.signature = requester_obj.signature
        signer_obj.F = signer_obj.signature[1]
        self.assertTrue(signer_obj.verify())

PeterSurda · 2019-08-27T13:34:44Z

let me try...

- add blind signature functionality to pyelliptic as described in Bitmessage#1409 - add tests for blind signatures - PEP8 fixes for pyelliptic - some minor refactoring is necessary for further integration, this is just a minimal implementation to pass a test

PeterSurda · 2019-08-27T21:22:01Z

@g1itch here you go.

g1itch · 2019-08-28T09:46:50Z

src/tests/test_blindsig.py

+        requester_obj = ECCBlind(pubkey=signer_obj.pubkey)
+        # only 64 byte messages are planned to be used in Bitmessage
+        msg = os.urandom(64)
+        msg_blinded = requester_obj.create_signing_request(point_r, msg)


Maybe self.assertNotEqual(msg, msg_blinded)?

Well that will always succeed as msg is a string and msg_blinded is an openssl bignum, but I can convert it before comparison, and I can also compare blinded an unblinded signature (those should both be bignums already).

As I said before, there is still no serialisation for the wire protocol, as that has to be designed first, then there will be minor refactoring here.

They will obviously differ. That's just a tests logic (as I understand it) to compare just in case and document it. Maybe that's unnecessary.

Serialization will be probably done in the network package, so it's not related to the blind signature implementation itself. The signatures seems to work well. So are you going to merge this now?

I'll add the tests and then merge.

- primitive serialisation (BN_bn2bin and ctypes) used in intermediary tests

PeterSurda · 2019-08-28T11:25:05Z

@g1itch I added tests to compare signature with blinded signature, and message with blinded message, all in form which serialises data to bytes with OpenSSL.BN_bn2bin and ctypes.cast. I think this format is usable on wire but more tests are needed.

PeterSurda added enhancement New feature developers The issue is relevant mainly for developers rather than users test labels Aug 26, 2019

PeterSurda added this to the Undefined milestone Aug 26, 2019

PeterSurda requested a review from g1itch August 26, 2019 15:50

PeterSurda force-pushed the blindsig1 branch from fe23699 to 70cf14d Compare August 26, 2019 15:58

PeterSurda force-pushed the blindsig1 branch 2 times, most recently from 14e56bf to 1c50db5 Compare August 26, 2019 16:50

g1itch approved these changes Aug 27, 2019

View reviewed changes

PeterSurda force-pushed the blindsig1 branch from 1c50db5 to f2cc835 Compare August 27, 2019 10:33

g1itch reviewed Aug 27, 2019

View reviewed changes

PeterSurda added 3 commits August 27, 2019 23:13

Import path changes as requested

076aeaa

Minor refactoring to separate objects

b934c4e

PeterSurda force-pushed the blindsig1 branch from d0907f3 to b934c4e Compare August 27, 2019 21:21

g1itch reviewed Aug 28, 2019

View reviewed changes

Add intermediary tests

395fbcd

- primitive serialisation (BN_bn2bin and ctypes) used in intermediary tests

PeterSurda merged commit 395fbcd into Bitmessage:v0.6 Aug 28, 2019

Blind signature support in pyelliptic #1509

Blind signature support in pyelliptic #1509

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PeterSurda commented Aug 28, 2019

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