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From: Kalle Rosenbaum <kalle@rosenbaum.se>
Date: Fri, 17 Jan 2025 11:38:28 +0100
Message-ID: <CAPswA9xbtbEfj-QmnAXj1m1R+Gap-Bd9vs8ed1ueA5gGtD-pYw@mail.gmail.com>
Subject: Re: [bitcoindev] Who uses or wants to use PSBTv2 (BIP370)
To: Salvatore Ingala <salvatore.ingala@gmail.com>
Cc: Sjors Provoost <sjors@sprovoost.nl>, bitcoindev@googlegroups.com
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I might have linked to a slightly outdated version of ledger's psbtv2. I
haven't been involved lately. The correct one could be
https://github.com/LedgerHQ/app-bitcoin-new/blob/53dfd1727ab55182f9e365747b26b862e48b7b8b/bitcoin_client_js/src/lib/psbtv2.ts.
Is that right, Salvatore?

/Kalle

On Fri, 17 Jan 2025 at 11:03, Salvatore Ingala <salvatore.ingala@gmail.com>
wrote:

> Hi Sjors,
>
> The Ledger Bitcoin app uses PSBTv2 since version 2.0.0 in 2021 [0], quite
> possibly the first adopter - although for somewhat unusual reasons.
>
> Working with embedded devices with just a few kb of RAM, even sending the
> entire PSBT is not generally feasible.
> Therefore, the client instead sends a 'merkleized' commitment to the
> entire PSBT at the beginning of the signing process.
> This enables the device to obtain random access to the PSBT by querying
> the client (who provides the data - and the Merkle proof - on demand).
>
> In PsbtV0, the unsigned transaction is a binary blob, which was a huge
> headache because the device had to parse it while streaming it (and
> therefore, no RAM access to the individual transaction fields is possible).
> PsbtV2 fixed this by having the transaction already 'parsed' into
> individual fields.
>
> The companion client libraries of the Ledger Bitcoin app support both
> versions, and PsbtV0 is converted to PsbtV2 on the fly.
> Broader support would certainly be useful.
>
> Best,
> Salvatore Ingala
>
> [0] https://www.ledger.com/blog/bitcoin-2
>
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> https://groups.google.com/d/msgid/bitcoindev/CAMhCMoGONKFok_SuZkic%2BT%3DyoWZs5eeVxtwJL6Ei%3DyysvA8rrg%40mail.gmail.com
> <https://groups.google.com/d/msgid/bitcoindev/CAMhCMoGONKFok_SuZkic%2BT%3DyoWZs5eeVxtwJL6Ei%3DyysvA8rrg%40mail.gmail.com?utm_medium=email&utm_source=footer>
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>

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<div dir=3D"ltr">I might have linked to a slightly outdated version of ledg=
er&#39;s psbtv2. I haven&#39;t been involved lately. The correct one could =
be=C2=A0<a href=3D"https://github.com/LedgerHQ/app-bitcoin-new/blob/53dfd17=
27ab55182f9e365747b26b862e48b7b8b/bitcoin_client_js/src/lib/psbtv2.ts">http=
s://github.com/LedgerHQ/app-bitcoin-new/blob/53dfd1727ab55182f9e365747b26b8=
62e48b7b8b/bitcoin_client_js/src/lib/psbtv2.ts</a>. Is that right, Salvator=
e?<br><br>/Kalle</div><br><div class=3D"gmail_quote gmail_quote_container">=
<div dir=3D"ltr" class=3D"gmail_attr">On Fri, 17 Jan 2025 at 11:03, Salvato=
re Ingala &lt;<a href=3D"mailto:salvatore.ingala@gmail.com">salvatore.ingal=
a@gmail.com</a>&gt; wrote:<br></div><blockquote class=3D"gmail_quote" style=
=3D"margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding=
-left:1ex"><div dir=3D"ltr"><div dir=3D"ltr">Hi=C2=A0Sjors,<div><br></div><=
div>The Ledger Bitcoin app uses PSBTv2 since version 2.0.0 in 2021 [0], qui=
te possibly the first adopter - although for somewhat unusual reasons.</div=
><div><br></div><div>Working with embedded devices with just a few kb of RA=
M, even sending the entire PSBT is not generally feasible.<br>Therefore, th=
e client instead sends a &#39;merkleized&#39; commitment to the entire PSBT=
 at the beginning of the signing process.</div><div>This enables the device=
 to obtain random access to the PSBT by querying the client (who provides t=
he data - and the Merkle proof - on demand).<br><br>In PsbtV0, the unsigned=
 transaction is a binary blob, which was a huge headache because the device=
 had to=C2=A0parse it while streaming it (and therefore, no RAM access to t=
he individual transaction fields is possible).<br>PsbtV2 fixed this by havi=
ng the transaction already &#39;parsed&#39; into individual fields.</div></=
div><div><br></div><div>The companion client libraries of the Ledger Bitcoi=
n app support both versions, and PsbtV0 is converted to PsbtV2 on the fly.<=
/div><div>Broader support would certainly be useful.</div><div><br></div><d=
iv>Best,</div><div>Salvatore Ingala</div><div><br></div><div>[0]=C2=A0<a hr=
ef=3D"https://www.ledger.com/blog/bitcoin-2" target=3D"_blank">https://www.=
ledger.com/blog/bitcoin-2</a></div></div>

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</blockquote></div>

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