> You were of course in fact pubkey-prefixing here (with the hash-160 of P) Yes, I also thought about that. But then, it means after around 2^80 operations, you could have a potential RIPEMD-160 collision in the future. Which also means, that 160-bit hashes may be later unsafe anyway. And if you pick 256-bit ones, then putting x-value pubkey gives the same size. Also, I wonder if collisions in P2SH will be used as a "wrapped Taproot". Because then, instead of building some MAST, it could be possible to simply prepare a collision, and use older addresses in that way. Then, Alice can for example use " OP_CHECKSIG", and Bob can use " OP_CHECKLOCKTIMEVERIFY OP_DROP OP_CHECKSIG". If applying HASH160 to both scripts will give the same 160-bit value, then each party could use a different Script, to spend coins from the same P2SH address. wt., 17 mar 2026 o 20:01 waxwing/ AdamISZ napisał(a): > Hi sashabeton, > > Apologies - I didn't read your proposal carefully. You were of course in > fact pubkey-prefixing here (with the hash-160 of P), so my entire saga > about pubkey prefixing is not actually relevant! > > (maybe someone found it interesting tho' , lol). > > Cheers, > AdamISZ/waxwing > > On Tuesday, March 17, 2026 at 3:00:50 PM UTC-3 waxwing/ AdamISZ wrote: > >> Hi sashabeton, >> >> > Honestly, this idea might have had better timing a few years ago. >> >> No I don't think so; it was discussed at the time (specifically, pubkey >> recovery). I remember bringing it up in the taproot review sessions on IRC. >> I'm sure others, including the taproot designers, discussed this issue well >> before I thought about it :) >> >> Perhaps this clarifies it for other mailing list readers: >> >> BIP340 Schnorr signatures are the form of Schnorr signature which has >> what is commonly termed "pubkey prefixing"; the challenge hash is e = H(R, >> P, m) with P the public key. This makes a pubkey recovery algorithm of the >> type that we have in our legacy ECDSA signatures, impossible. It's a point >> of not-only-historical interest that the original Schnorr signature design >> was H(R, m) not H(R, P, m) and that even around the time when ECDSA was >> being designed to avoid the Schnorr patent, and later, it was a point of >> considerable contention amongst various system designers, whether pubkey >> prefixing was needed or not. >> >> Pubkey prefixing makes all of the security reductions much more >> meaningful, since it can make the concept of "resistant to forgery" much >> more wide-ranging and powerful (in short, imagine the idea that you can >> make up a schnorr signature for some arbitrary key that wasn't used before >> .. this is sorta kinda true for non-pubkey-prefixed Schnorr). And that has >> big implications for perhaps the biggest application of Schnorr in Bitcoin, >> which is aggregation; aggregation in a bitcoin context means *aggregating >> arbitrary, new, ephemeral keys*, not keys previously recorded in some >> certificate registry or whatever. You're not going to get sensible versions >> of MuSig without pubkey prefixing, because you couldn't stop adversaries >> making up malicious keys that they don't have to commit to. >> >> Without that kind of aggregation scheme (and see e.g. DahLIAS and CISA, >> if you don't actually care about multisig for whatever reason; it could end >> up being very important for Bitcoin scaling anyway), Schnorr is a lot less >> of an upgrade to our signing algorithm (though to be fair, still not >> nothing, it's on sounder theoretical foundations). >> >> Cheers, >> AdamISZ/waxwing >> >> On Tuesday, March 17, 2026 at 6:32:12 AM UTC-3 sashabeton wrote: >> >>> Hi everyone, >>> >>> After reading all the feedback, I think it's time to accept that this >>> proposal has no realistic path forward. >>> >>> For it to make sense, the new address type would need to be adopted by >>> the entire ecosystem almost instantly — which is simply not going to happen. >>> >>> Honestly, this idea might have had better timing a few years ago. Today, >>> the landscape has moved on, and I don't think pushing this further would be >>> a good use of anyone's time. >>> >>> I want to thank everyone who took the time to read, review, and respond. >>> >>> On Tuesday, 17 March 2026 at 08:32:06 UTC+1 Saint Wenhao wrote: >>> >>>> > The goal is giving users who are already happy with the P2WPKH model >>>> (no script spending, simple single-key payments) the witness efficiency of >>>> Schnorr >>>> >>>> If you have a DER signature, then it can take from 9 to 73 bytes. In >>>> Schnorr signatures, it is set to 64 or 65 bytes. >>>> >>>> In practice, you can have 71 bytes without grinding, which means, that >>>> by using a CPU to grind r-value and s-value, to shrink it by 4 bytes each, >>>> you will get 63 bytes in a DER signature. And that won't reveal your >>>> private key to anyone else. It would require around 2^33 operations, so it >>>> is doable on CPUs. >>>> >>>> Which means, that if you want to have smaller signatures, and you are >>>> willing to put some Proof of Work into that, then you will get better >>>> results by just staying with P2WPKH. And, as leading zeroes are not pushed >>>> in DER signatures, because of BIP-66, and as computing power is getting >>>> better and better, your signatures could be smaller in the future, while in >>>> Schnorr signatures, you won't have any way to go below 64 bytes. >>>> >>>> pon., 16 mar 2026 o 17:12 sashabeton napisał(a): >>>> >>>>> To clarify the design intent: P2SKH is not a stripped-down Taproot — >>>>> it is P2WPKH upgraded to Schnorr. The starting point is P2WPKH (compact >>>>> 20-byte hash commitment, no script path, single-key payments), and the only >>>>> change is replacing ECDSA with the same Schnorr signature scheme Taproot's >>>>> key-path uses. That's it. >>>>> >>>>> The goal is giving users who are already happy with the P2WPKH model >>>>> (no script spending, simple single-key payments) the witness efficiency of >>>>> Schnorr without forcing them onto a 34-byte output type designed for a >>>>> richer feature set they don't need. >>>>> >>>>> P2SKH is not quantum-resistant — I fully acknowledge this. Like >>>>> P2WPKH, it relies on secp256k1 and will need to be migrated once >>>>> post-quantum schemes are deployed in Bitcoin. But until that happens, it >>>>> serves the same users as P2WPKH today, just more efficiently. When the time >>>>> comes, users migrate — the same way P2PKH and P2WPKH users will have to. >>>>> >>>>> On Monday, 16 March 2026 at 16:45:32 UTC+1 Alex wrote: >>>>> >>>>>> > In that use case P2TR key-path spending offers no scriptability >>>>>> either — this is not a new trade-off, it is the same one Taproot already >>>>>> made. >>>>>> >>>>>> This is not true. Taproot has 2 modes; its key-spend path is 12 bytes >>>>>> more bloated than your solution, yes. but Taproot can "dynamically" chose >>>>>> whether to use the key-spend path or the script-spend path. Your solution >>>>>> fully removes the script spend path, so you're not really optimizing an >>>>>> equally capable solution, you're optimizing for only 1 part of it. >>>>>> >>>>>> Removing scriptability for 12 bytes could possibly be warranted in >>>>>> some specific cases (I'm sure there are cases), but it's not a fair >>>>>> comparison against Taproot or BIP360. And since we will need quantum >>>>>> upgrade at some point, this upgrade is kind of (in my personal >>>>>> interpretation) doubling down to the part that will eventually break. >>>>>> >>>>>> Do you have any plan on how one could quantum secure the funds in >>>>>> P2SKH? >>>>>> måndag 16 mars 2026 kl. 12:57:52 UTC+1 skrev Alex: >>>>>> >>>>>>> You are saving 12 bytes by removing all the scriptability, OP-code >>>>>>> upgradeability and basically locking yourself to a non-quantum-secure key >>>>>>> spend path that is only quantum secure if never spent? Or did I >>>>>>> missunderstand? >>>>>>> >>>>>>> måndag 16 mars 2026 kl. 12:25:57 UTC+1 skrev Martin Habovštiak: >>>>>>> >>>>>>>> Taproot specifically did not do this for good reasons that are well >>>>>>>> documented. I recommend you to read documentation first before attempting >>>>>>>> to make changes. >>>>>>>> >>>>>>>> Dňa po 16. 3. 2026, 11:48 sashabeton >>>>>>>> napísal(a): >>>>>>>> >>>>>>>>> Hi everyone, >>>>>>>>> >>>>>>>>> I'd like to propose a new native SegWit output type: Pay to >>>>>>>>> Schnorr Key Hash (P2SKH). >>>>>>>>> >>>>>>>>> == The problem == >>>>>>>>> >>>>>>>>> The two most relevant output types today each solve half the >>>>>>>>> problem: >>>>>>>>> - P2WPKH has a compact 22-byte scriptPubKey, but uses ECDSA and >>>>>>>>> puts the full 33-byte compressed public key in the witness (~108 witness >>>>>>>>> bytes per input). >>>>>>>>> - P2TR uses Schnorr signatures (64-byte witness), but embeds the >>>>>>>>> full 32-byte x-only public key directly in the scriptPubKey, making outputs >>>>>>>>> 12 bytes larger than P2WPKH and exposing the key in every unspent output. >>>>>>>>> >>>>>>>>> Neither type achieves both a compact output and a compact witness >>>>>>>>> simultaneously. >>>>>>>>> >>>>>>>>> == The proposal == >>>>>>>>> >>>>>>>>> P2SKH uses OP_2 as the scriptPubKey (22 bytes, same >>>>>>>>> as P2WPKH). Spending requires a single 64-byte Schnorr signature. >>>>>>>>> Verification works by key recovery: given the signature (R, s) and the >>>>>>>>> challenge e = TaggedHash("P2SKH/challenge", R.x || hash160(P.x) || msg), >>>>>>>>> the verifier recovers P = e^-1 * (s*G - R) and checks that hash160(P.x) >>>>>>>>> matches the program. The sighash reuses the BIP341 transaction digest, so >>>>>>>>> cross-version replay is prevented by the scriptPubKey commitment. >>>>>>>>> >>>>>>>>> The result is the smallest combined footprint of any current >>>>>>>>> single-key output type — a 22-byte output with a 64-byte witness — while >>>>>>>>> keeping the public key off-chain until spending. >>>>>>>>> >>>>>>>>> == Tradeoffs == >>>>>>>>> >>>>>>>>> The key-recovery step costs roughly one extra field inversion and >>>>>>>>> scalar multiplication compared to direct Schnorr verification. This is the >>>>>>>>> price of the 12-byte output size reduction. >>>>>>>>> >>>>>>>>> == Open questions == >>>>>>>>> >>>>>>>>> 1. BIP360 also claims witness version 2. If both proposals >>>>>>>>> advance, one needs to move. Version 3 seems like a natural alternative for >>>>>>>>> P2SKH. >>>>>>>>> 2. Naming — "P2SKH" follows the established pattern but "P2TRKH" >>>>>>>>> has been suggested to emphasise Schnorr/taproot lineage. Opinions welcome. >>>>>>>>> >>>>>>>>> Full draft: >>>>>>>>> https://github.com/sashabeton/bips/blob/3cb9e07984b571e9510370ab7e7218620be580dc/p2skh.md >>>>>>>>> PoC implementation: https://github.com/bitcoin/bitcoin/pull/34826 >>>>>>>>> >>>>>>>>> Thanks in advance for any feedback. >>>>>>>>> >>>>>>>>> -- >>>>>>>>> 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+...@googlegroups.com. >>>>>>>>> To view this discussion visit >>>>>>>>> https://groups.google.com/d/msgid/bitcoindev/3dcadd5d-702a-4e6c-ad6c-2ddfe68ec73en%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+...@googlegroups.com. >>>>> >>>> To view this discussion visit >>>>> https://groups.google.com/d/msgid/bitcoindev/ee240078-88c6-4961-8412-489a77012038n%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/fc83173c-f4b3-4a2e-a662-dd6eecebb7ban%40googlegroups.com > > . > -- You received this message because you are subscribed to the Google Groups "Bitcoin Development Mailing List" group. 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