From: Dragi Bucukovski <dragi.b@icloud.com>
Content-Type: text/plain;
	charset=utf-8
Content-Transfer-Encoding: quoted-printable
Mime-Version: 1.0 (1.0)
Date: Mon, 9 Sep 2019 14:47:17 +1000
Message-Id: <05D1AEA5-5374-4183-AE19-8E071C13AEA8@icloud.com>
References: <CAPv7TjaE1wF-25R=LaOES33A78ovDAp9-waiC7n5YLJnMmNs9A@mail.gmail.com>
	<uVQNn9hhpqlQuS-RzrUkpClVtegMRUoyIL6ITaYfNkjd_XYyu9Fh9vdAeLguzOyOrNx5FtuHk7yyZAdivqCVR2PKzF_PsoWJlsSY9oJTF7s=@protonmail.com>
In-Reply-To: <uVQNn9hhpqlQuS-RzrUkpClVtegMRUoyIL6ITaYfNkjd_XYyu9Fh9vdAeLguzOyOrNx5FtuHk7yyZAdivqCVR2PKzF_PsoWJlsSY9oJTF7s=@protonmail.com>
To: ZmnSCPxj <ZmnSCPxj@protonmail.com>,
	Bitcoin Protocol Discussion <bitcoin-dev@lists.linuxfoundation.org>
Subject: Re: [bitcoin-dev] PoW fraud proofs without a soft fork
Precedence: list

How much do I have in my account can you please tell me=20

Sent from my iPhone

> On 9 Sep 2019, at 2:14 pm, ZmnSCPxj via bitcoin-dev <bitcoin-dev@lists.lin=
uxfoundation.org> wrote:
>=20
> Good morning Ruben,
>=20
>=20
>>    One might intuitively feel that the lack of a commitment is unsafe,
>>    but there seems to be no impact on security (only bandwidth). The only=

>>    way you can be fooled is if all peers lie to you (Sybil), causing you
>>    to follow a malicious minority chain. But even full nodes (or the
>>    committed version of PoW fraud proofs) can be fooled in this way if
>>    they are denied access to the valid most PoW chain. If there are
>>    additional security concerns I overlooked, I=E2=80=99d love to hear th=
em.
>=20
>=20
> I think it would be better to more precisely say that:
>=20
> 1.  In event of a sybil attack, a fullnode will stall and think the blockc=
hain has no more miners.
> 2.  In event of a sybil attack, an SPV, even using this style, will follow=
 the false blockchain.
>=20
> This has some differences when considering automated systems.
>=20
> Onchain automated payment processing systems, which use a fullnode, will r=
efuse to acknowledge any incoming payments.
> This will lead to noisy complaints from clients of the automated payment p=
rocessor, but this is a good thing since it warns the automated payment proc=
essor of the possibility of this attack occurring on them.
> The use of a timeout wherein if the fullnode is unable to see a new block f=
or, say, 6 hours, could be done, to warn higher-layer management systems to p=
ay attention.
> While it is sometimes the case that the real network will be unable to fin=
d a new block for hours at a time, this warning can be used to confirm if su=
ch an event is occurring, rather than a sybil attack targeting that fullnode=
.
>=20
> On the other hand, such a payment processing system, which uses an SPV wit=
h PoW fraud proofs, will be able to at least see incoming payments, and cont=
inue to release product in exchange for payment.
> Yet this is precisely a point of attack, where the automated payment proce=
ssing system is sybilled and then false payments are given to the payment pr=
ocessor on the attack chain, which are double-spent on the global consensus c=
hain.
> And the automated system may very well not be able to notice this.
>=20
> Regards,
> ZmnSCPxj
> _______________________________________________
> bitcoin-dev mailing list
> bitcoin-dev@lists.linuxfoundation.org
> https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev