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Thu, 21 May 2026 03:00:24 -0700 (PDT) X-Received: by 2002:a05:6808:66d3:b0:482:ce3b:12e5 with SMTP id 5614622812f47-4852ec73151mr669871b6e.14.1779357624765; Thu, 21 May 2026 03:00:24 -0700 (PDT) Received: by 2002:a05:690c:6202:b0:7ba:f1b3:9504 with SMTP id 00721157ae682-7c6993cf1f6ms7b3; Thu, 21 May 2026 02:56:12 -0700 (PDT) X-Received: by 2002:a05:690c:25c9:b0:7ba:f690:70be with SMTP id 00721157ae682-7d209bd2e39mr21622577b3.7.1779357372059; Thu, 21 May 2026 02:56:12 -0700 (PDT) Date: Thu, 21 May 2026 02:56:11 -0700 (PDT) From: "Nuh.dev" To: Bitcoin Development Mailing List Message-Id: <8e069e17-c819-4c30-b4d7-917b9561813bn@googlegroups.com> In-Reply-To: References: <0aadce7a-b08b-4fd2-8bae-37df1cfc54afn@googlegroups.com> <4516f3ab-0715-4dd9-825c-eed4eac3065a@thinlink.com> Subject: Re: [bitcoindev] Re: Fly Client Proposal MIME-Version: 1.0 Content-Type: multipart/mixed; boundary="----=_Part_107234_2140859033.1779357371380" X-Original-Sender: Ar.Nazeh@gmail.com Precedence: list Mailing-list: list bitcoindev@googlegroups.com; contact bitcoindev+owners@googlegroups.com List-ID: X-Google-Group-Id: 786775582512 List-Post: , List-Help: , List-Archive: , List-Unsubscribe: , X-Spam-Score: -0.5 (/) ------=_Part_107234_2140859033.1779357371380 Content-Type: multipart/alternative; boundary="----=_Part_107235_126896584.1779357371380" ------=_Part_107235_126896584.1779357371380 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable To make a counter argument to mine, and assuming Bitcoin soft forks are not= =20 impossible, FlyClient has an advantage that is impossible to replicate with= =20 ZK proofs; they are simple enough that one can reason about and implement= =20 from scratch similar to implementing an SPV, whereas formally proving ZK=20 Starks end to end is very unlikely to happen any time soon, and reviewing= =20 all of its complexity is impossible for any single mortal. The same argument applies for validating Sidechains by the way, you can use= =20 a ZK proof, but I am increasingly thinking that a FlyClient verifier native= =20 in Bitcoin as an opcode, is orders of magnitude safer and easier to=20 implement. So I encourage you and everyone to not give up on FlyClient in Bitcoin yet. On Tuesday, 19 May 2026 at 00:07:54 UTC+3 Zac Mitton wrote: > Ok, Let's keep this thread about Flyclient on Bitcoin. The challenges=20 > related to actually getting a soft-fork into bitcoin are best discussed= =20 > elsewhere. > > If anyone has information related to progress on this,=20 > or implementation ideas please help by posting here or DMing me. I will t= ry=20 > to aggregate. > > On Mon, May 4, 2026 at 12:26=E2=80=AFPM Tom Harding = wrote: > >> Zac,=20 >> >> That's probably because the question, and my post, are off-topic. They= =20 >> are not about FlyClient, which is not interesting to me because bitcoin'= s=20 >> header chain is tiny. >> >> Instead they touch on two techniques which would improve on most=20 >> historical implementations of SPV clients by adding protocol support for= =20 >> them. >> >> Sorry for the distraction. >> >> Tom >> >> >> On 5/3/26 12:26, Zac Mitton wrote: >> >> Tom I can=E2=80=99t seem to grok the question or your explanation of it.= Could=20 >> you spell it out for us in detail? >> >> >> Thanks, Zac >> >> On Sun, May 3, 2026 at 12:58=E2=80=AFPM Tom Harding = wrote: >> >>> In the linked presentation by Benedict B=C3=BCnz, it's worth listening = to the=20 >>> first audience question/answer. Questioner is spot on that an SPV clie= nt=20 >>> polling the network to gain probabilistic confidence of unspentness cou= ld=20 >>> easily subsume the task of gaining input inclusion proofs from the netw= ork,=20 >>> with no forking change necessary. >>> >>> On Wednesday, April 29, 2026 at 2:03:36=E2=80=AFPM UTC-7 Zac Mitton wro= te: >>> >>>> Hi, Ive been looking into FlyClient first described here=20 >>>> . I don't see= any=20 >>>> BIPs, or previous discussion in this forum about it either.=20 >>>> >>>> On bitcoin It could allow a light-client to verify the entire work of= =20 >>>> the heaviest chain with a single ~100KB proof. >>>> >>>> It can theoretically be done as a soft-fork by injecting a single hash= =20 >>>> into the coinbase tx (similar to how segwit is committed to).=20 >>>> >>>> What do you guy's think? >>>> >>> >>> --=20 You received this message because you are subscribed to the Google Groups "= Bitcoin Development Mailing List" group. To unsubscribe from this group and stop receiving emails from it, send an e= mail to bitcoindev+unsubscribe@googlegroups.com. To view this discussion visit https://groups.google.com/d/msgid/bitcoindev/= 8e069e17-c819-4c30-b4d7-917b9561813bn%40googlegroups.com. ------=_Part_107235_126896584.1779357371380 Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable To make a counter argument to mine, and assuming Bitcoin soft forks are not= impossible, FlyClient has an advantage that is impossible to replicate wit= h ZK proofs; they are simple enough that one can reason about and implement= from scratch similar to implementing an SPV, whereas formally proving ZK S= tarks end to end is very unlikely to happen any time soon, and reviewing al= l of its complexity is impossible for any single mortal.

The sam= e argument applies for validating Sidechains by the way, you can use a ZK p= roof, but I am increasingly thinking that a FlyClient verifier native in Bi= tcoin as an opcode, is orders of magnitude safer and easier to implement.
So I encourage you and everyone to not give up on FlyClient in Bi= tcoin yet.

On Tuesday, 19 May 2026 at 00:07:54 UTC+3 Zac Mitton wrote:
Ok, Let's keep this thread about Flyclient on Bitcoin. The challenges= related to actually getting a soft-fork into bitcoin are best discussed el= sewhere.

If anyone has information related to progress o= n this, or=C2=A0implementation=C2=A0ideas please help by posting here or DM= ing me. I will try to aggregate.

=
On Mon, May 4, 2026 at 12:26=E2=80=AF= PM Tom Harding <to...@thinlin= k.com> wrote:
=20 =20 =20

Zac,=C2=A0

That's probably because the question, and my post, are off-topic.=C2=A0 They are not about FlyClient, which is not interesti= ng to me because bitcoin's header chain is tiny.

Instead they touch on two techniques which would improve on most historical implementations of SPV clients by adding protocol support for them.

Sorry for the distraction.

Tom


On 5/3/26 12:26, Zac Mitton wrote:
=20
Tom I can=E2=80=99t seem to grok the question or yo= ur explanation of it. Could you spell it out for us in detail?


Thanks, Zac

On Sun, May 3, 2026 at 12:58=E2=80=AFPM Tom Harding <to...@thinlink.com> wrote:
In the linked presentation by Benedict B=C3=BCnz, it's= worth listening to the first audience question/answer.=C2=A0 Questioner is spot on that an SPV client polling the network to gain probabilistic confidence of unspentness could easily subsume the task of gaining input inclusion proofs from the network, with no forking change necessary.
On Wednesday, April 29= , 2026 at 2:03:36=E2=80=AFPM UTC-7 Zac Mitton wrote:
Hi, Ive been looking into FlyClient first described here. I don't see any BIPs, or previous discussion in this forum about it either.

On bitcoin It could allow a light-client to verify the entire work of the heaviest chain with a single ~100KB proof.

It can theoretically be done as a soft-fork by injecting a single hash into the coinbase tx (similar to how segwit is committed to).=C2=A0

What do you guy's think?

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