From: "Martin Habovštiak" <martin.habovstiak@gmail.com>
To: sashabeton <sashabeton2007@gmail.com>
Cc: Bitcoin Development Mailing List <bitcoindev@googlegroups.com>
Subject: Re: [bitcoindev] [BIP proposal] Pay to Schnorr Key Hash (P2SKH)
Date: Mon, 16 Mar 2026 17:25:36 +0100 [thread overview]
Message-ID: <CALkkCJaZ8150yWFLGe6NUuBrNE_N5AnekaqrG=NcnWy1zWUQHQ@mail.gmail.com> (raw)
In-Reply-To: <ee240078-88c6-4961-8412-489a77012038n@googlegroups.com>
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It doesn't matter because it competes with Taproot and that is the problem.
People should be migrating from old schemes to Taproot to maximize anonset
of Taproot, not to $a_new_key_only_scheme or Taproot.
Forcing users to use Taproot even if they don't need scripting is a
desirable feature and intentional design from the beginning. 12B is
justified cost for better privacy.
Dňa po 16. 3. 2026, 17:12 sashabeton <sashabeton2007@gmail.com> napísal(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 <sashabe...@gmail.com> 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 <hash160(P.x)> 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.
>>>>>
>>>>> --
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>>>>> https://groups.google.com/d/msgid/bitcoindev/3dcadd5d-702a-4e6c-ad6c-2ddfe68ec73en%40googlegroups.com
>>>>> <https://groups.google.com/d/msgid/bitcoindev/3dcadd5d-702a-4e6c-ad6c-2ddfe68ec73en%40googlegroups.com?utm_medium=email&utm_source=footer>
>>>>> .
>>>>>
>>>> --
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next prev parent reply other threads:[~2026-03-23 9:54 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-03-16 8:51 sashabeton
2026-03-16 11:12 ` Martin Habovštiak
2026-03-16 11:43 ` Alex
2026-03-16 14:36 ` sashabeton
2026-03-16 15:57 ` Martin Habovštiak
2026-03-16 15:43 ` Alex
2026-03-16 16:00 ` sashabeton
2026-03-16 16:25 ` Martin Habovštiak [this message]
2026-03-24 6:02 ` aaron.recompile
2026-03-16 19:29 ` Alex
2026-03-17 7:23 ` Saint Wenhao
2026-03-17 7:40 ` sashabeton
2026-03-17 18:00 ` waxwing/ AdamISZ
2026-03-17 18:30 ` waxwing/ AdamISZ
2026-03-18 5:24 ` Saint Wenhao
2026-03-18 15:50 ` "wrapped Taproot" from RIPEMD-160 collisions, Was: " Ethan Heilman
2026-03-16 11:38 ` Saint Wenhao
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