Private Bitcoin Payments — Last Week in Bitcoin (Sep 21 - 27)

Sep 28, 2026

Hi Insiders. This is Tuma, open-source reporter from the Insider Edition.

In this week’s update we feature some new NUT specifications currently being discussed for improving the Cashu protocol.

We also cover Shielded Bitcoin, a new protocol by [[alloc]init] to private bitcoin transactions, the new plugin by Second for simplifying accepting Bitcoin through BTCPayServer, Ben Carman’s work to include Lightning in the x402 specifications, and the latest maintenance release for Core-Lightning.

Highlights from the Bitcoin developer ecosystem

I spent 10+ hours in open-source developer calls in the Bitcoin ecosystem last week. Here is what caught my eye:

The Cashu ecosystem is working on implementing new features and proposing new NUT specifications.
- During the monthly community calls, on Thursday 24th, Cashu developers discussed the latest news from the ecosystem. In particular, they presented new additions to the NUT specifications.
- PR433 introduces compact state filter, a concept similar to compact block filters (BIP158) available on Bitcoin. This new feature aims to increase the privacy of the protocol by allowing a wallet to retrieve the information about the state of a token locally, without providing the mint with all the token identifiers. Instead, the mint would provide the wallet with filters containing the state of a token.
- PR450 adds an optional NUT that allows a mint to publish a bid and an ask price on its own liquidity. Since there are several payment methods available for minting and melting — LN, on-chain, Bark —, this NUT would allow the mint to set different prices on the liquidity available on different payment methods, thus attracting liquidity where needed the most.

A BIPs Update

In the last days there was some movement in the BIP repository. Specifically, one new BIP has been published by BIP maintainer Murchandamus.

Published BIPs

A list of recently published BIPs

BIP138: Compact encryption scheme for non-seed wallet data

Authors: Pyth

Published On: Sep 21st, 2026

Layer: Applications

BIP138 specifies a compact encryption scheme for output descriptors, wallet policies, labels, and wallet backup metadata to allow users to store sensible information on untrusted media. The encryption key is derived from the public keys in the descriptor, allowing any keyholder to decrypt the data without additional secrets.

Other News from the Bitcoin World

Shielded Bitcoin: [[alloc]init] presented a new metaprotocol to make Bitcoin transactions more private, called Shielded Bitcoin. The proposal — presented in a dedicated paper by Clara Shikhelman, Misha Komarov, and Aleksei Moskvin — does not require neither changes to the Bitcoin consensus, nor operators or trusted third parties.
- A Shielded Bitcoin transaction is a blob of data included in an on-chain transaction through an OP_RETURN or other data-carrying fields. The transaction validation is demanded to an external node, called Indexer, which has also the task to update the state of an output.
- Shielded Bitcoin uses a specific type of output, called note, which plays a similar role as a Bitcoin UTXO. However, while UTXOs are deleted from the set once they are consumed, notes are spent by posting a proof and nullifier. To check whether a note has been spent or not, a user checks if its nullifier has already been used or not.
- For what concerns the peg, the protocol uses Bitcoin PIPEs v2. This is a witness encryption method that can be used to reproduce covenant semantics without changes to Bitcoin consensus. Basically, instead of locking a certain output behind a spending condition, it allows a user to specify those conditions on the key needed to move those funds, adding prerequisites on whether a valid signature can be produced or not.
Bark <> BTCPayServer: Second — the company behind the Ark implementation Bark — announced that their plugin for BTCPayServer was available for use in production.
- Historically, BTCPayServer has relied on Lightning to allow merchants to accept Bitcoin payments. That meant taking on all the difficulties of running a full Lightning node, such as channel management, liquidity, and maintenance.
- The new Bark plugin allows merchants to accept Bitcoin without all of that. Users will now be able to run their self-hosted BTCPayServer instance without running a Lightning node behind and to accept self-custodial, instant Bitcoin payment in a simpler way.
Lightning <> x402: LDK maintainer Ben Carman announced that Lightning had been officially included in the x402 specifications.
- x402 is an open standard for native internat payments built on top of HTTP. It is currency-agnostic, which mean that it can support any payment rail, such as Bitcoin, stablecoins, and fiat. It is supported by some of the biggest corporations in the world, such as Amazon, Amex, Google, Mastercard, but also by come big companies in the wider crypto industry, such as Ripple, Coinbase, Solana.
- Given the companies involved, it is not surprising that Bitcoin had not been added yet to the x402 standard. Ben Carman was able to close this gap, pushing for the inclusion of Lightining in the specifications.
CLN Release: The Core-lightning team announced the release of a new maintenance version of the Lightning node software, v26.06.8. This version includes several fixes for bugs and vulnerabilities that were responsibly disclosed in the last weeks. Contrary to the previous version, no embargo was put on this release, making the source code available from the beginning. However, the team noted that some tests were withheld from publication to prevent attackers from reverse-engineering the vulnerabilities.

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