Sending Silent Payments with PSBTs

The five-minute read

One action, walked through

1. Open BIP 375 and read the status line before the examples.
2. Write down the rule in one sentence. A fair version of that sentence is: This document specifies new fields and new field inclusion/exclusion requirements.
3. Name the object that changes: ECDH, PSBT_GLOBAL_SP_ECDH_SHARE, DLEQ.
4. Ask what an old client, an old contract, or an offline counterparty does. If the document is silent, the silence is part of the design.

The argument, unpacked

What has to be true

• You are implementing BIP 375 at the status the text itself states: Draft.
• The object that has to change is ECDH, PSBT_GLOBAL_SP_ECDH_SHARE, DLEQ. A neighbouring document with a similar name is not this one.
• Wallet support is not the same as consensus validity.

What happened after the paper

The source marks this draft. It is not a live consensus rule just because it has a number. Later documents can narrow, replace, or ignore this one. Cite the number you mean.

What to check before you use the idea

• What is covered by the signed bytes in Sending Silent Payments with PSBTs?
• Can the same signature be replayed on another chain, account, or message?
• Which primitive does the text require: ECDH, PSBT_GLOBAL_SP_ECDH_SHARE, DLEQ?

Terms

BIP 375

The public text titled Sending Silent Payments with PSBTs.

Draft

The document's own label for how finished the text is. It is not a market fact.

The problem the paper names

A signature that does not commit to what the user saw can be replayed into a different spend, a different chain, or a different message.

What the design proposes

• This document specifies new fields and new field inclusion/exclusion requirements.
• The new global types are defined as follows: {| ! Name ! ! ! Description ! ! Description ! Versions Requiring Inclusion ! Versions Requiring Exclusion ! Versions Allowing Inclusion |- | Silent Payment Global ECDH Share | PSBT_GLOBAL_SP_ECDH_SHARE = 0x07 | | The scan key that this ECDH share is for.
• The ECDH shared is computed with ''a B_scan'', where ''a'' is the sum of all private keys of all eligible inputs, and ''B_scan'' is the scan key of a recipient.

How the mechanism is specified

• Taken from the specification, the next constraint is: The new global types are defined as follows: {| ! Name ! ! ! Description ! ! Description ! Versions Requiring Inclusion ! Versions Requiring Exclusion ! Versions Allowing Inclusion |- | Silent Payment Global ECDH Share | PSBT_GLOBAL_SP_ECDH_SHARE = 0x07 | | The scan key that this ECDH share is for.
• Locate ECDH, PSBT_GLOBAL_SP_ECDH_SHARE, DLEQ in BIP 375 and apply it to one transaction or call.
• Then check the failure the class of rule always has: a node that did not upgrade, a reverted call, a replayed signature, or a peer that does not speak the message.

What this page does not treat as proven

• A signature scheme is not a privacy system. It hides the signer only if the protocol says so.
• Wallet support is not the same as consensus validity.
• The source marks this draft. It is not a live consensus rule just because it has a number.

Why a venture studio still reads it

Use BIP 375 when a pitch says 'Sending Silent Payments with PSBTs' without saying whether the rule is consensus, policy, or an interface. The number is the citation. The pitch is not.