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To: woltx <woltx@protonmail.com>
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Cc: Bitcoin Protocol Discussion <bitcoin-dev@lists.linuxfoundation.org>
Subject: Re: [bitcoin-dev] joinstr: coinjoin implementation using nostr
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Hi woltx,

> I've been reviewing joinstr, and if I understand the code correctly, the =
cryptographic scheme mentioned as an alternative to blind signatures isn't =
implemented yet, is it? Currently, it seems that anyone can submit unrelate=
d inputs and outputs.

Thanks for reviewing joinstr. Yes, its not implemented right now as it requ=
ires a NIP and at least one relay using it.

> Instead of clients sending descriptors to the relay and then verifying th=
em using `scantxoutset`, it can send `txid:out` with a message signed with =
the address, verify using `verifymessage` and then use `gettxout` to retrie=
ve the value. That way, only the owner can send the UTXO.

`scantxoutset` is only used to get UTXO details (txid, vout and amount) as =
I thought its easier for users to just share a descriptor for coinjoin.=20

If a user sends `txid:out` with a message signed with the address, this wou=
ld be publicly available to everyone connected to same relay and links an i=
nput with output. Responding with a secret shared by relay for the round co=
nfirms user owns one of the input but does not reveal exact input.


/dev/fd0


Sent with Proton Mail secure email.

------- Original Message -------
On Friday, September 9th, 2022 at 9:05 PM, woltx <woltx@protonmail.com> wro=
te:


> Hi /dev/fd0,
>=20
> I've been reviewing joinstr, and if I understand the code correctly, the =
cryptographic scheme mentioned as an alternative to blind signatures isn't =
implemented yet, is it? Currently, it seems that anyone can submit unrelate=
d inputs and outputs.
>=20
> Perhaps PR #24058 (https://github.com/bitcoin/bitcoin/pull/24058) (basic =
support BIP-322) can improve this scheme as it implements proof of ownershi=
p.
>=20
> Instead of clients sending descriptors to the relay and then verifying th=
em using `scantxoutset`, it can send `txid:out` with a message signed with =
the address, verify using `verifymessage` and then use `gettxout` to retrie=
ve the value. That way, only the owner can send the UTXO.
>=20
> I've done some tests connected to a node with BIP322 enabled:
>=20
> # to send
> input_txt: str =3D json.dumps(input)
> result =3D core.signmessage(wallet, input['address'], input_txt)
> input['signature'] =3D result['result']
> nostr_interface.publish_input(input)
>=20
> # to receive
> def validate_input(input: dict[str, int, str, str]) -> bool:
>=20
> # ...
> result =3D core.verifymessage(address=3Dinput['address'], message=3Djson.=
dumps(message), signature=3Dinput['signature'])
> return result['error'] =3D=3D None and result['result'] =3D=3D True
>=20
>=20
>=20
>=20
>=20
> ------- Original Message -------
> On Saturday, August 20th, 2022 at 1:52 PM, alicexbt via bitcoin-dev bitco=
in-dev@lists.linuxfoundation.org wrote:
>=20
>=20
>=20
> > Hi Max,
> >=20
> > There a few DoS vectors that need to be fixed. Its just a proof of conc=
ept that I wanted to share with everyone to get feedback which could be imp=
roved over time. There is also a warning at the bottom of README to not use=
 this on mainnet as it might have bugs.
> >=20
> > I will continue the development with coinjoin transactions on signet fo=
r a few weeks until there is a stable release with no bugs.
> >=20
> > I have a few ideas in mind for various relay types that might be used c=
oncurrently to prevent numerous problems. Custom relays are supported by No=
str. Examples include paying a fee to register for a round, subscribing wit=
h a time limit, or using invite-only relays. I will run a free and open nos=
tr relay for this project and try to fix the Dos issues before a mainnet ve=
rsion is released for python script(for nerds) and android app (for all use=
rs).
> >=20
> > Related links:
> >=20
> > https://github.com/fiatjaf/relayer
> > https://github.com/fiatjaf/expensive-relay
> > https://github.com/fiatjaf/relayer/tree/master/whitelisted
> >=20
> > /dev/fd0
> >=20
> > Sent with Proton Mail secure email.
> >=20
> > ------- Original Message -------
> > On Saturday, August 20th, 2022 at 10:04 AM, Max Hillebrand max@towardsl=
iberty.com wrote:
> >=20
> > > Great to see an implementation of the idea.
> > >=20
> > > Maybe I misunderstand, but isn't there a vulnerability of denial of s=
ervice here?
> > >=20
> > > A user who registers one input will receive the round secret identifi=
er, and this is all the information required for output registration. Howev=
er, that malicious user can now register multiple outputs, providing the sa=
me secret, and nobody can link the malicious outputs to any specific input.=
 Therefor there cannot be a blame round where the malicious input is remove=
d, and thus there can be a ongoing free denial of service attack without at=
tribution or defense.
> > >=20
> > > Skol
> > > Max
> > >=20
> > > On August 20, 2022 10:20:00 AM GMT+02:00, alicexbt via bitcoin-dev bi=
tcoin-dev@lists.linuxfoundation.org wrote:
> > >=20
> > > > Hi Bitcoin Developers,
> > > >=20
> > > > I have written a python script as proof of concept for the coinjoin=
 implementation using nostr. I used a lot of Python scripts created by othe=
rs in school, so it feels nice to offer something that could be useful to o=
thers.
> > > >=20
> > > > The implementation uses Bitcoin Core wallet and RPCs: `listunspent`=
, `getnewaddress`, `scantxoutset`, `createpsbt`, `combinepsbt`, `finalizeps=
bt` and `sendrawtransaction`. It requires python-nostr library because nost=
r is used for coordination between peers. Nostr is a decentralized network =
based on cryptographic keypairs. It is not peer-to-peer however simple and =
scalable.
> > > >=20
> > > > Every step is published as an event using a nostr relay and 5 peers=
 coordinate to create, sign and broadcast a coinjoin transaction. I need to=
 write a NIP that would be an alternative to blind signatures. Relay will s=
hare a random secret with clients for one round which should be present in =
output registration request although never gets published. If someone tries=
 to register an output without registering any inputs, request would not ha=
ve the number initially shared with inputs so request would get rejected or=
 published as unverified. Relay would not be able to link inputs and output=
s as the number is same for all inputs in a round and they get registered a=
t different times with new keys and IP address. Clients can use multiple re=
lays at the same time to avoid trusting one relay. This would result in dif=
ferent shared secret number but same process. If a relay tries to cheat, us=
ers will not sign the transaction and avoid using it in future.
> > > >=20
> > > > Usage:
> > > >=20
> > > > 1)Run `python coinjoin.py` and enter descriptor for one of the inpu=
ts.
> > > > 2)Script will check inputs for this round in every 30 seconds and r=
egister a new adddress for output once 5 inputs are registered.
> > > > 3)Similar check happens every 30 seconds for outputs. Last peer sho=
uld create a PSBT.
> > > > 4)Unsigned PSBT will be printed and signed by wallet with `walletpr=
ocesspsbt` RPC.
> > > > 5)Script will check signed PSBTs and last peer to sign should final=
ize coinjoin transaction once 5 signed PSBTs are received.
> > > > 6)Coinjoin transaction will be broadcasted and txid will printed.
> > > >=20
> > > > Example:
> > > >=20
> > > > ```
> > > > List of utxos in wallet:
> > > >=20
> > > > wpkh([53830dca/84'/1'/0'/0/0]02449be5fb74725255eeeb50eba930fa87705f=
21e99d13cd710cf2c1f21153c808)#x2hyyeg5
> > > >=20
> > > > Enter descriptor for the input registration: wpkh([53830dca/84'/1'/=
0'/0/0]02449be5fb74725255eeeb50eba930fa87705f21e99d13cd710cf2c1f21153c808)#=
x2hyyeg5
> > > >=20
> > > > event id: bcbbe62d75d99fed73f1e50ac58a38d1840b658951893e63c0322b378=
d7d56f0
> > > >=20
> > > > tb1qhxrp4zl54ul0twtyz0gury5399q7z0kvqqrl6m registered for output
> > > >=20
> > > > event id: 9449c9065bef356d21507a98f88b028b17fc1c49eb195c8d4420604fc=
aaef041
> > > >=20
> > > > Unsigned PSBT: cHNidP8BAP1yAQIAAAAFtMaoJYcXvOG5L3Yaz3YyS7gIt4h5/zzO=
rRRS3hrVvwoAAAAAAP////+o83geaSm4L76KToIUl5MiZqLAUbIDJLq6DWrjP/3b8AEAAAAA///=
//zEF3CXIvVHpIa7No1s1yg+KtyOfXTRSyWnOdXMfzcDwAQAAAAD/////wMa4XAgnU+39Ien+KG=
9rYtv8bLMNYakmZyY/QFfwLRcAAAAAAP/////5M42ID6uLmQTb2tnFHnN7UMpnDD25uN8ZX7A+G=
NSM3QEAAAAA/////wV4xwEAAAAAABYAFLmGGov0rz71uWQT0cGSkSlB4T7MeMcBAAAAAAAWABSc=
0/FM6Hdbdxh10IJkYOklVFWqjnjHAQAAAAAAFgAUPSZKe/w6PT6qIF+WhL4wHaFymjd4xwEAAAA=
AABYAFMx0rxYlpPWB3NFry4Ctk2eVi/UNeMcBAAAAAAAWABSzc4xK0VTfvjK0MHXrAUFLYgYnOg=
AAAAAAAAAAAAAAAAAAAA=3D=3D
> > > >=20
> > > > event id: 976744b38fa9343fb79e1b5215512ead6ee08e5890d79a201fc5b872f=
6de4eba
> > > >=20
> > > > Signed PSBT: cHNidP8BAP1yAQIAAAAFtMaoJYcXvOG5L3Yaz3YyS7gIt4h5/zzOrR=
RS3hrVvwoAAAAAAP////+o83geaSm4L76KToIUl5MiZqLAUbIDJLq6DWrjP/3b8AEAAAAA/////=
zEF3CXIvVHpIa7No1s1yg+KtyOfXTRSyWnOdXMfzcDwAQAAAAD/////wMa4XAgnU+39Ien+KG9r=
Ytv8bLMNYakmZyY/QFfwLRcAAAAAAP/////5M42ID6uLmQTb2tnFHnN7UMpnDD25uN8ZX7A+GNS=
M3QEAAAAA/////wV4xwEAAAAAABYAFLmGGov0rz71uWQT0cGSkSlB4T7MeMcBAAAAAAAWABSc0/=
FM6Hdbdxh10IJkYOklVFWqjnjHAQAAAAAAFgAUPSZKe/w6PT6qIF+WhL4wHaFymjd4xwEAAAAAA=
BYAFMx0rxYlpPWB3NFry4Ctk2eVi/UNeMcBAAAAAAAWABSzc4xK0VTfvjK0MHXrAUFLYgYnOgAA=
AAAAAQBxAgAAAAG+qpMXZCy6tBuUlgo8JD0GVXKp60FkhwDeg2sF1fkFkwMAAAAA/f///wLo9wE=
AAAAAABYAFFfLA5xarC/w/SxeMDQ5tuXrYJLUWwMAAAAAAAAWABRfPf//hwMjHB4OKj87cU19XO=
Sh7yOWAQABAR/o9wEAAAAAABYAFFfLA5xarC/w/SxeMDQ5tuXrYJLUAQhrAkcwRAIgOIhLoC534=
8U8YkEr4GU1K4yWskIOEXgW4Wsk/W2cR7ICIEJXqtOuDJ5CkwrSuwJLWtzab4dslbN3KuL/pyoo=
MnOCASECRJvl+3RyUlXu61DrqTD6h3BfIemdE81xDPLB8hFTyAgAAAAAACICA77Cnd6o3kr0yc+=
91eabpOn5igs/MUMbudNYSS6oyMWMGFODDcpUAACAAQAAgAAAAIAAAAAAFAAAAAAAAAAA
> > > >=20
> > > > event id: 5846b6e6902f3c5a43496d7d9785ed62444aa74963f03c33d637d8b09=
ee7a139
> > > >=20
> > > > Coinjoin tx: 75e490b10b15a6a0422f25ff66ad98ef70390c8fecaac02712705d=
ce8cc3564b
> > > >=20
> > > > event id: 9b5d4bf279b59e2b6e539e683fba83da72dce2b640360aa95db1b1400=
be93190
> > > > ```
> > > >=20
> > > > There are lot of things that could be improved and a few suggestion=
s are in the gist that described the idea. I would love read to any opinion=
s about this experiment and will start working on creating an Android app f=
or joinstr next week.
> > > >=20
> > > > Credits:
> > > >=20
> > > > - fiatjaf (Nostr)
> > > > - Andrew Chow (PSBT)
> > > > - Jeff Thibault (python-nostr)
> > > > - Existing coinjoin implmentations
> > > >=20
> > > > /dev/fd0
> > > >=20
> > > > Sent with Proton Mail secure email.
> > > >=20
> > > > bitcoin-dev mailing list
> > > > bitcoin-dev@lists.linuxfoundation.org
> > > > https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev
> >=20
> > _______________________________________________
> > bitcoin-dev mailing list
> > bitcoin-dev@lists.linuxfoundation.org
> > https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev