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[2a00:1450:4864:20::62d]) by gmr-mx.google.com with ESMTPS id 4fb4d7f45d1cf-6475103ad91si197880a12.8.2025.11.29.09.03.28 for (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sat, 29 Nov 2025 09:03:28 -0800 (PST) Received-SPF: pass (google.com: domain of earonesty@gmail.com designates 2a00:1450:4864:20::62d as permitted sender) client-ip=2a00:1450:4864:20::62d; Received: by mail-ej1-x62d.google.com with SMTP id a640c23a62f3a-b7355f6ef12so561211366b.3 for ; Sat, 29 Nov 2025 09:03:28 -0800 (PST) X-Gm-Gg: ASbGncu886x4C9O398Ns7yrYkchxbqwlLcFzBD23j0LgpOxrNDVzC15QeYsoNEGMGrL 74ANmeVdRctJEvEm39ZKImYPLrzkUHEI68s69nm16pr7kCaO8nlSY9g+enUGDRcxWQ8/IRcK3j/ 2v4SbVSVVDaP6smh3BwpSy2N3TJbxr7Gj48l/tLHGL2KPgIvqZ52DtuON2cL9ReaHc2Y0bZ/dsf jp7TbXAeWRtUIDe4wvrfIajvOcqoFXd2StbexjwEAGlpteRhxlZyOq9yddleyaYFvPoIVB9Tymz UQIQa2Te+OPRVMrwby3Ft1aIkSFQDQ== X-Received: by 2002:a17:907:9288:b0:b76:23df:c997 with SMTP id a640c23a62f3a-b76718977d5mr3671467966b.54.1764435807358; Sat, 29 Nov 2025 09:03:27 -0800 (PST) MIME-Version: 1.0 References: <1d1c5d9c-9b36-4e4b-930c-d23b2f562052n@googlegroups.com> In-Reply-To: <1d1c5d9c-9b36-4e4b-930c-d23b2f562052n@googlegroups.com> From: Erik Aronesty Date: Sat, 29 Nov 2025 09:03:15 -0800 X-Gm-Features: AWmQ_blVIeQnnjc-6dwq8ZjXJdBrVAFO1G8AgxxoZpeynoAfBgI-h9JwOFuDxp4 Message-ID: Subject: Re: [bitcoindev] A safe way to remove objectionable content from the blockchain To: "waxwing/ AdamISZ" Cc: Bitcoin Development Mailing List Content-Type: multipart/alternative; boundary="00000000000086d4710644beb9b9" X-Original-Sender: erik@q32.com X-Original-Authentication-Results: gmr-mx.google.com; dkim=pass header.i=@q32-com.20230601.gappssmtp.com header.s=20230601 header.b=ufTvZpii; spf=pass (google.com: domain of earonesty@gmail.com designates 2a00:1450:4864:20::62d as permitted sender) smtp.mailfrom=earonesty@gmail.com; dara=pass header.i=@googlegroups.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: -0.7 (/) --00000000000086d4710644beb9b9 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable there is no fundamental change to the cryptography. The beacon proofs are only used for "proof of not spam". The proven Bitcoin key is the same secp256k1 key and spending is unchanged. uxto proofs are not terribly unreasonable given the cost of UTXOs On Sat, Nov 29, 2025, 8:15=E2=80=AFAM waxwing/ AdamISZ = wrote: > Hi Erik, > > > You can stop arbitrary data encoding in public keys by requiring every > key to be the **unique hash-to-curve output** of a publicly verifiable BL= S > root signature, rather than a user-chosen point on secp256k1. > > Indeed, absolutely correct (afaik!), I had recently been discussing this = a > bit with Lloyd Fournier on nostr. I think at a theoretical level this is = a > very important observation, but at a practical level not so much. It's al= so > worth noting that something like RSA FDH or hash based signatures, since > they're deterministic (think "no nonce" and no technical ZK property) cou= ld > technically do the same thing, but BLS is far and away better than those. > > Theoretical not practical: I think there's no way such a thing would > happen on bitcoin (IMO! could be wrong!) because it's an absolutely huge > change to the crypto without improving quantum resistance (performance > issues are I guess an open question, considering batching properties vs r= aw > performance of a single pairing being bad). And the other reason: no poin= t > going this far without attempting to patch *every* hole that allows data > that is not trivial. You could argue these holes are trivial: amount data= , > locktimes (both nLockTime and nSequence), in/out sequencing not being > deterministic, and grinding curve points. The obviously much more relevan= t > and non-trivial issue is Script, generally, and sort of peripheral to > script stuff like control block in taproot etc. Since you'd have to > "address" (that is to say, gut) Bitcoin's scripting before these other > things like deterministic signatures become relevant, it does seem all ve= ry > theoretical, if interesting. > > I guess this would have been better in the "On (in)ability to embed data > in Schnorr" thread but w/e it's all kind of connected I guess! > > Cheers, > AdamISZ/waxwing > > On Saturday, November 29, 2025 at 12:43:56=E2=80=AFPM UTC-3 Erik Aronesty= wrote: > >> You can stop arbitrary data encoding in public keys by requiring every >> key to be the **unique hash-to-curve output** of a publicly verifiable B= LS >> root signature, rather than a user-chosen point on secp256k1. >> >> Because a BLS signature is checkable via a pairing equation, verifiers >> can confirm that each public key was deterministically forced by the roo= t >> certificate and not selected to embed arbitrary bits. Under this >> construction, public keys become outputs of a constrained randomness bea= con >> rather than an open steganographic channel. >> >> In practice, the system fixes a BLS12-381 public key `PK_root` and a >> one-time BLS signature `=CF=83 =3D Sign_root(S)`. Any allowed secp256k1 = key is >> then defined as `P_i =3D HashToCurve_secp256k1(=CF=83 || i)`, where `i` = is an >> arbitrary index and the hash-to-curve map is a standard indifferentiable >> encoding (e.g., IETF RFC 9380). Verifiers check the pairing equation `e(= =CF=83, >> g) =3D e(H(S), PK_root)` once, and thereafter reject any public key whos= e >> curve point does not equal the canonical hash-to-curve output for some >> disclosed index `i`. Because the signer never chooses curve points=E2=80= =94and >> because hash-to-curve eliminates degrees of freedom=E2=80=94no entropy r= emains to >> smuggle bits into the key, satisfying the same non-malleability criteria >> used in anti-steganographic constructions. >> >> This =E2=80=9Cforced randomness=E2=80=9D model parallels techniques in t= he literature on >> steganographic resistance and extractable commitments, particularly >> Hopper=E2=80=93Langford=E2=80=93von Ahn=E2=80=99s work on *provably secu= re steganography* and >> Bellare=E2=80=93Ristenpart=E2=80=93Tessaro=E2=80=99s analyses of *channe= l indistinguishability* in >> public-key spaces. >> >> The underlying idea is identical: eliminate sender choice over >> high-entropy objects so the objects cannot become covert storage. >> >> >> On Sat, Nov 29, 2025, 5:57=E2=80=AFAM waxwing/ AdamISZ wrote: >> >>> Hi Peter, list, >>> >>> Interesting! >>> >>> One thought that springs to mind: attempts to ameliorate IBD with ZKP >>> should not forget one thing: what we actually want here is succinctness= , >>> and not so much ZK. Think SNARK instead of ZkSNARK. >>> Which is important; without the requirement for an actual ZK property >>> for the protocol, you can have it have attached witness that is not sec= ret. >>> >>> Then a counter-thought strikes, that any version of these protocols tha= t >>> requires more data/bandwidth probably loses out to versions that have l= ess >>> data/bandwidth. Hmm. >>> >>> It seems to demonstrate, to me, that some kind of "data carrying" is >>> required in the "state" (cf the "history"). Ironically recent discussio= n >>> (see 'On (in)ability to embed data into Schnorr' but yeah a googolplex = of >>> "discussions" on the internet about filtering and spam...) has just >>> re-emphasized that the utxo set can inevitably carry data (I guess that= 's >>> obvious). >>> >>> I do think, long term that ZKP over history is correct, and that (see >>> typical rollup design) data carrying in state can do the job that you a= re >>> (correctly) insisting, must be done. >>> (And the corollary: "harmful data on the blockchain" is a wrong mental >>> model and should be abandoned, irrespective of architecture.) >>> >>> Aside from your *main* concept here, I think the idea that HTLCs requir= e >>> *proof* of publication is wrong. What they require is publication. A >>> wronged channel party needs to read the preimage, not have proof that i= t >>> can be read. Take as contrast the opentimestamps model, where having pr= oof >>> that something was published, is the main functionality offered/require= d. I >>> suppose there is another way to say it: the channel counterparty needs >>> "proof of future publication" in contract setup. That's fair enough but >>> it's a very different thing than getting a proof that something *was* >>> published. >>> >>> Cheers, >>> AdamISZ/waxwing >>> >>> On Saturday, November 29, 2025 at 8:32:21=E2=80=AFAM UTC-3 Peter Todd w= rote: >>> >>>> On Thu, Nov 20, 2025 at 04:21:33PM -0500, Ethan Heilman wrote: >>>> > I'm not convinced your hash function approach fully does what you >>>> want it >>>> > to, although it does seem doable with some additional constraints. >>>> > >>>> > There is a solution that does everything you want it and more, ZKPs. >>>> > >>>> > ZKP (Zero Knowledge Proofs) can prove that some data X hashes to som= e >>>> hash >>>> > output Y while keeping the actual value X secret. Thus, everyone can >>>> be >>>> > convinced that H(X) =3D Y even if X is deleted and no one knows what >>>> the >>>> > value X was. >>>> > >>>> > Even more exciting, ZKPs can prove the correctness and validity of >>>> the >>>> > entire Bitcoin blockchain. Thus storing old transactions is >>>> > no longer needed to convince others that the chain is correct. This >>>> would >>>> > remove any harmful data. Zerosync in 2017 compressed Bitcoin's >>>> blockchain >>>> > into a 800 KB proof [0] which is constant size regardless of the >>>> number of >>>> > transactions or bytes compressed. This approach does not require any >>>> > changes to Bitcoin and you could implement a Bitcoin full node today >>>> that >>>> > supports this. >>>> > >>>> > We have a solution to solve the problem of harmful data on the >>>> blockchain >>>> > since 2017. It just requires time, money and motivated people to wor= k >>>> on it. >>>> >>>> Rather than being a solution, the technology behind Zerosync is a >>>> potential >>>> threat to Bitcoin. The problem is that Bitcoin fundamentally requires >>>> proof-of-publication to be decentralized and censorship resistant; a >>>> related >>>> problem is that HTLCs (and thus Lightning) fundamentally requires >>>> proof-of-publication to work at all. >>>> >>>> For Bitcoin mining to remain decentralized, blocks need to be widely >>>> propagated >>>> in a form suitable for creating new blocks. ZKP/Zerosync makes it >>>> possible to >>>> prove that a block hash and all prior blocks follow the protocol rules >>>> and were >>>> thus valid. However, valid block hashes alone are insufficient to mine >>>> on top >>>> of because they do not contain the UTXO set data necessary to mine a >>>> new block. >>>> >>>> Why do miners have an incentive to distribute the blocks they find? >>>> Ultimately >>>> because doing so is necessary for the coins they mined to be valuable. >>>> But if >>>> full nodes can be convinced of the validity of coins without full bloc= k >>>> contents --- thus allowing those coins to be sold --- that weakens the >>>> incentives to distribute block data in a form that allows other miners >>>> to mine. >>>> >>>> >>>> With regard to HTLCs/Lightning, HTLCs rely on a proof-of-publication t= o >>>> be >>>> secure: for the HTLC to be redeemed, the redeemer *must* publish the >>>> pre-image >>>> in the Bitcoin chain, allowing the other party relying on the HTLC to >>>> recover >>>> the pre-image. Again, ZKP/Zerosync weakens this security, as the >>>> validity of >>>> the transaction spending the HTLC can be proven without actually makin= g >>>> the >>>> pre-image available. >>>> >>>> >>>> Rather than presenting ZKP/Zerosync as a solution to the "harmful data= " >>>> problem, we should in fact be researching ways to defeat ZKP/Zerosync >>>> entirely. >>>> We need a consensus protocol where the only way to fully validate a >>>> block is to >>>> actually have the entire block contents. >>>> >>>> As for "harmful data", that is a challenge to be solved >>>> legally/politically. >>>> >>>> -- >>>> https://petertodd.org 'peter'[:-1]@petertodd.org >>>> >>> -- >>> >> You received this message because you are subscribed to the Google Group= s >>> "Bitcoin Development Mailing List" group. >>> To unsubscribe from this group and stop receiving emails from it, send >>> an email to bitcoindev+...@googlegroups.com. >>> >> To view this discussion visit >>> https://groups.google.com/d/msgid/bitcoindev/f5cf7fb8-61ce-437b-b26b-24= 1d47b3fcb5n%40googlegroups.com >>> >>> . >>> >> -- > 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 > email to bitcoindev+unsubscribe@googlegroups.com. > To view this discussion visit > https://groups.google.com/d/msgid/bitcoindev/1d1c5d9c-9b36-4e4b-930c-d23b= 2f562052n%40googlegroups.com > > . > --=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/= CAJowKg%2BNuZcowZhKvTH9Dij-8eiM0pueX8Ym8RbqUHOfE5Nbjg%40mail.gmail.com. --00000000000086d4710644beb9b9 Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable
there is no fundamental change to the cryptography.=C2=A0= The beacon proofs are only used for "proof of not spam".=C2=A0 T= he proven Bitcoin key is the same secp256k1 key and spending is unchanged.= =C2=A0 uxto proofs are not terribly unreasonable given the cost of UTXOs=C2= =A0

On Sat, Nov 29, 2025, 8:15=E2=80=AFAM waxwing/ Ada= mISZ <ekaggata@gmail.com> w= rote:
Hi Erik,

<= /div>
> You can stop arbitrary data encoding in public keys by requi= ring every=20 key to be the **unique hash-to-curve output** of a publicly verifiable=20 BLS root signature, rather than a user-chosen point on secp256k1.=C2=A0

Indeed, absolutely correct (afaik!), I had recently b= een discussing this a bit with Lloyd Fournier on nostr. I think at a theore= tical level this is a very important observation, but at a practical level = not so much. It's also worth noting that something like RSA FDH or hash= based signatures, since they're deterministic (think "no nonce&qu= ot; and no technical ZK property) could technically do the same thing, but = BLS is far and away better than those.

Theoretical= not practical: I think there's no way such a thing would happen on bit= coin (IMO! could be wrong!) because it's an absolutely huge change to t= he crypto without improving quantum resistance (performance issues are I gu= ess an open question, considering batching properties vs raw performance of= a single pairing being bad). And the other reason: no point going this far= without attempting to patch *every* hole that allows data that is not triv= ial. You could argue these holes are trivial: amount data, locktimes (both = nLockTime and nSequence), in/out sequencing not being deterministic, and gr= inding curve points. The obviously much more relevant and non-trivial issue= is Script, generally, and sort of peripheral to script stuff like control = block in taproot etc. Since you'd have to "address" (that is = to say, gut) Bitcoin's scripting before these other things like determi= nistic signatures become relevant, it does seem all very theoretical, if in= teresting.

I guess this would have been better in = the "On (in)ability to embed data in Schnorr" thread but w/e it&#= 39;s all kind of connected I guess!

Cheers,
<= div>AdamISZ/waxwing

On Saturday, November 29, 2025 at 12:43:56=E2=80=AFPM U= TC-3 Erik Aronesty wrote:
You can stop arbitrary data encoding in public keys = by requiring every key to be the **unique hash-to-curve output** of a publi= cly verifiable BLS root signature, rather than a user-chosen point on secp2= 56k1.=C2=A0

Because a BLS sign= ature is checkable via a pairing equation, verifiers can confirm that each = public key was deterministically forced by the root certificate and not sel= ected to embed arbitrary bits. Under this construction, public keys become = outputs of a constrained randomness beacon rather than an open steganograph= ic channel.

In practice,= the system fixes a BLS12-381 public key `PK_root` and a one-time BLS signa= ture `=CF=83 =3D Sign_root(S)`. Any allowed secp256k1 key is then defined a= s `P_i =3D HashToCurve_secp256k1(=CF=83 || i)`, where `i` is an arbitrary i= ndex and the hash-to-curve map is a standard indifferentiable encoding (e.g= ., IETF RFC 9380). Verifiers check the pairing equation `e(=CF=83, g) =3D e= (H(S), PK_root)` once, and thereafter reject any public key whose curve poi= nt does not equal the canonical hash-to-curve output for some disclosed ind= ex `i`. Because the signer never chooses curve points=E2=80=94and because h= ash-to-curve eliminates degrees of freedom=E2=80=94no entropy remains to sm= uggle bits into the key, satisfying the same non-malleability criteria used= in anti-steganographic constructions.

This =E2=80=9Cforced randomness=E2=80=9D model parallels tec= hniques in the literature on steganographic resistance and extractable comm= itments, particularly Hopper=E2=80=93Langford=E2=80=93von Ahn=E2=80=99s wor= k on *provably secure steganography* and Bellare=E2=80=93Ristenpart=E2=80= =93Tessaro=E2=80=99s analyses of *channel indistinguishability* in public-k= ey spaces.=C2=A0

The und= erlying idea is identical: eliminate sender choice over high-entropy object= s so the objects cannot become covert storage.

<= /div>

=
On Sat, Nov 29, 2025, 5:57=E2=80=AFAM= waxwing/ AdamISZ <ekag...@gmail.com&= gt; wrote:
Hi Peter, list,

Interesting!

One thought that springs to mind: attempts to ameliorate = IBD with ZKP should not forget one thing: what we actually want here is suc= cinctness, and not so much ZK. Think SNARK instead of ZkSNARK.
Wh= ich is important; without the requirement for an actual ZK property for the= protocol, you can have it have attached witness that is not secret.
<= div>
Then a counter-thought strikes, that any version of thes= e protocols that requires more data/bandwidth probably loses out to version= s that have less data/bandwidth. Hmm.

=C2=A0It see= ms to demonstrate, to me, that some kind of "data carrying" is re= quired in the "state" (cf the "history"). Ironically re= cent discussion (see 'On (in)ability to embed data into Schnorr' bu= t yeah a googolplex of "discussions" on the internet about filter= ing and spam...) has just re-emphasized that the utxo set can inevitably ca= rry data (I guess that's obvious).

I do think,= long term that ZKP over history is correct, and that (see typical rollup d= esign) data carrying in state can do the job that you are (correctly) insis= ting, must be done.
(And the corollary: "harmful data on the= blockchain" is a wrong mental model and should be abandoned, irrespec= tive of architecture.)

Aside from your *main* conc= ept here, I think the idea that HTLCs require *proof* of publication is wro= ng. What they require is publication. A wronged channel party needs to read= the preimage, not have proof that it can be read. Take as contrast the ope= ntimestamps model, where having proof that something was published, is the = main functionality offered/required. I suppose there is another way to say = it: the channel counterparty needs "proof of future publication" in contract setup. That's fair= enough but it's a very different thing than getting a proof that something *was*= =20 published.

Cheers,
AdamISZ/waxwing
=

On Saturday, November 29, 2025 at 8:32:21=E2=80=AFAM UTC-3 Peter Todd= wrote:
On Thu, Nov 20= , 2025 at 04:21:33PM -0500, Ethan Heilman wrote:
> I'm not convinced your hash function approach fully does what = you want it
> to, although it does seem doable with some additional constraints.
>=20
> There is a solution that does everything you want it and more, ZKP= s.
>=20
> ZKP (Zero Knowledge Proofs) can prove that some data X hashes to s= ome hash
> output Y while keeping the actual value X secret. Thus, everyone c= an be
> convinced that H(X) =3D Y even if X is deleted and no one knows wh= at the
> value X was.
>=20
> Even more exciting, ZKPs can prove the correctness and validity of= the
> entire Bitcoin blockchain. Thus storing old transactions is
> no longer needed to convince others that the chain is correct. Thi= s would
> remove any harmful data. Zerosync in 2017 compressed Bitcoin's= blockchain
> into a 800 KB proof [0] which is constant size regardless of the n= umber of
> transactions or bytes compressed. This approach does not require a= ny
> changes to Bitcoin and you could implement a Bitcoin full node tod= ay that
> supports this.
>=20
> We have a solution to solve the problem of harmful data on the blo= ckchain
> since 2017. It just requires time, money and motivated people to w= ork on it.

Rather than being a solution, the technology behind Zerosync is a poten= tial
threat to Bitcoin. The problem is that Bitcoin fundamentally requires
proof-of-publication to be decentralized and censorship resistant; a re= lated
problem is that HTLCs (and thus Lightning) fundamentally requires
proof-of-publication to work at all.

For Bitcoin mining to remain decentralized, blocks need to be widely pr= opagated
in a form suitable for creating new blocks. ZKP/Zerosync makes it possi= ble to
prove that a block hash and all prior blocks follow the protocol rules = and were
thus valid. However, valid block hashes alone are insufficient to mine = on top
of because they do not contain the UTXO set data necessary to mine a ne= w block.

Why do miners have an incentive to distribute the blocks they find? Ult= imately
because doing so is necessary for the coins they mined to be valuable. = But if
full nodes can be convinced of the validity of coins without full block
contents --- thus allowing those coins to be sold --- that weakens the
incentives to distribute block data in a form that allows other miners = to mine.


With regard to HTLCs/Lightning, HTLCs rely on a proof-of-publication to= be
secure: for the HTLC to be redeemed, the redeemer *must* publish the pr= e-image
in the Bitcoin chain, allowing the other party relying on the HTLC to r= ecover
the pre-image. Again, ZKP/Zerosync weakens this security, as the validi= ty of
the transaction spending the HTLC can be proven without actually making= the
pre-image available.


Rather than presenting ZKP/Zerosync as a solution to the "harmful = data"
problem, we should in fact be researching ways to defeat ZKP/Zerosync e= ntirely.
We need a consensus protocol where the only way to fully validate a blo= ck is to
actually have the entire block contents.

As for "harmful data", that is a challenge to be solved legal= ly/politically.

--=20
https://petertodd.org 'peter'[:-1]@petertodd.org

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