Newsletters: add 346 (2025-03-21)

_posts/en/newsletters/2025-03-21-newsletter.md

@@ -0,0 +1,234 @@
+---
+title: 'Bitcoin Optech Newsletter #346'
+permalink: /en/newsletters/2025/03/21/
+name: 2025-03-21-newsletter
+slug: 2025-03-21-newsletter
+type: newsletter
+layout: newsletter
+lang: en
+---
+This week's newsletter summarizes a discussion about LND's updated
+dynamic feerate adjustment system.  Also included are our regular
+sections describing recent changes to services and client software,
+announcing new releases and release candidates, and summarizing recent
+merges to popular Bitcoin infrastructure software.
+
+## News
+
+- **Discussion of LND's dynamic feerate adjustment system:** Matt
+  Morehouse [posted][morehouse sweep] to Delving Bitcoin a description
+  of LND's recently-rewritten _sweeper_ system, which
+  determines the feerates to use for onchain transactions (including
+  [RBF][topic rbf] fee bumps).  He begins with a brief description
+  of the safety critical aspects of fee management for an LN node, as
+  well as the natural desire to avoid overpaying.  He then describes the
+  two general strategies used by LND:
+
+  - Querying external feerate estimators, such as a local Bitcoin Core
+    node or a third party.  This is mainly used for choosing initial
+    feerates and fee bumping non-urgent transactions.
+
+  - Exponential fee bumping, used when a deadline is approaching to
+    ensure that problems with a node's mempool or its [fee estimation][topic fee estimation]
+    don't prevent timely confirmation.  For example, Eclair uses exponential fee
+    bumping when deadlines are within six blocks.
+
+  Morehouse then describes how these two strategies are combined in
+  LND's new sweeper system: "[HTLC][topic htlc] claims with matching
+  deadlines [are aggregated] into a single [batched transaction][topic
+  payment batching]. The budget for the batched transaction is
+  calculated as the sum of the budgets for the individual HTLCs in the
+  transaction. Based on the transaction budget and deadline, a fee
+  function is computed that determines how much of the budget is spent
+  as the deadline approaches.  By default, a linear fee function is used,
+  which starts at a low fee (determined by the minimum relay fee rate or
+  an external estimator) and ends with the total budget being allocated
+  to fees when the deadline is one block away."
+
+  He additionally describes how the new logic helps protect against
+  [replacement cycling][topic replacement cycling] attacks, concluding:
+  "with LND’s default parameters an attacker must generally spend at
+  least 20x the value of the HTLC to successfully carry out a
+  replacement cycling attack."  He adds that the new system also
+  improves LND's defense against [pinning attacks][topic transaction
+  pinning].
+
+  He concludes with a link-filled summary of several "LND-specific bug
+  and vulnerability fixes" made through the improved logic.  Abubakar
+  Sadiq Ismail [replied][ismail sweep] with some suggestions for how all
+  LN implementations (in addition to other software) can more
+  effectively use Bitcoin Core's fee estimation.  Several other
+  developers also commented, adding both nuance to the description and
+  praise for the new approach.
+
+## Changes to services and client software
+
+*In this monthly feature, we highlight interesting updates to Bitcoin
+wallets and services.*
+
+- **Wally 1.4.0 released:**
+  The [libwally-core 1.4.0 release][wally 1.4.0] adds [taproot][topic
+  taproot] support, support for deriving [BIP85][] RSA keys, as well as additional
+  [PSBT][topic psbt] and [descriptor][topic descriptors] features.
+
+- **Bitcoin Core Config Generator announced:**
+  The [Bitcoin Core Config Generator][bccg github] project is a terminal interface
+  for creating Bitcoin Core `bitcoin.conf` configuration files.
+
+- **A regtest development environment container:**
+  The [regtest-in-a-pod][riap github] repository provides a [Podman][podman
+  website] container configured with Bitcoin Core, Electrum, and Esplora, as outlined
+  in the [Using Podman Containers for Regtest Bitcoin Development][podman
+  bitcoin blog] blog post.
+
+- **Explora transaction visualization tool:**
+  [Explora][explora github] is a web-based explorer for visualizing and
+  navigating between transaction inputs and outputs.
+
+- **Hashpool v0.1 tagged:**
+  [Hashpool][hashpool github] is a [mining pool][topic pooled mining] based on
+  the [Stratum v2 reference implementation][news247 sri] where mining shares are
+  represented as [ecash][topic ecash] tokens (see [Podcast #337][pod337 hashpool]).
+
+- **DMND launching pooled mining:**
+  [DMND][dmnd website] is launching Stratum v2 pooled mining, building on their
+  previous solo mining [announcement][news281 demand].
+
+- **Krux adds taproot and miniscript:**
+  [Krux][news273 krux] adds [miniscript][topic miniscript] and taproot support,
+  leveraging the [embit][embit website] library.
+
+- **Source-available secure element announced:**
+  The [TROPIC01][tropic01 website] is a secure element built on RISC-V with
+  an [open architecture][tropicsquare github] for auditability.
+
+- **Nunchuk launches Group Wallet:**
+  [Group Wallet][nunchuk blog] supports [multisignature][topic
+  multisignature] signing, taproot, coin control, [Musig2][topic musig], and
+  secure communication between participants by repurposing the output descriptors in the
+  [BIP129][] Bitcoin Secure Multisig Setup (BSMS) file.
+
+- **FROSTR protocol announced:**
+  [FROSTR][frostr github] uses the FROST [threshold signature scheme][topic
+  threshold signature] to achieve k-of-n signing and key management for nostr.
+
+- **Bark launches on signet:**
+  The [Bark][new325 bark] implementation of [Ark][topic ark] is now
+  [available][second blog] on [signet][topic signet] with a faucet and demo
+  store for testing.
+
+- **Cove Bitcoin wallet announced:**
+  [Cove Wallet][cove wallet github] is an open source Bitcoin mobile wallet based on
+  BDK that supports technologies like PSBTs, [wallet labels][topic wallet labels],
+  hardware signing devices, and more.
+
+## Releases and release candidates
+
+_New releases and release candidates for popular Bitcoin infrastructure
+projects.  Please consider upgrading to new releases or helping to test
+release candidates._
+
+- [Bitcoin Core 29.0rc2][] is a release candidate for the next major
+  version of the network's predominate full node.
+
+## Notable code and documentation changes
+
+_Notable recent changes in [Bitcoin Core][bitcoin core repo], [Core
+Lightning][core lightning repo], [Eclair][eclair repo], [LDK][ldk repo],
+[LND][lnd repo], [libsecp256k1][libsecp256k1 repo], [Hardware Wallet
+Interface (HWI)][hwi repo], [Rust Bitcoin][rust bitcoin repo], [BTCPay
+Server][btcpay server repo], [BDK][bdk repo], [Bitcoin Improvement
+Proposals (BIPs)][bips repo], [Lightning BOLTs][bolts repo],
+[Lightning BLIPs][blips repo], [Bitcoin Inquisition][bitcoin inquisition
+repo], and [BINANAs][binana repo]._
+
+- [Bitcoin Core #31649][] removes all checkpoint logic, which is no longer
+  necessary following the headers presync step implemented years ago (see
+  Newsletter [#216][news216 presync]) that enables a node during Initial Block
+  Download (IBD) to determine if a chain of headers is valid by comparing its
+  total proof of work (PoW) to a predefined threshold `nMinimumChainWork`. Only
+  chains with a total proof of work exceeding this value are considered valid
+  and stored, effectively preventing memory DoS attacks from low-work headers.
+  This eliminates the need for checkpoints, which were often seen as a
+  centralized element.
+
+- [Bitcoin Core #31283][] introduces a new `waitNext()` method to the
+  `BlockTemplate` interface, which will only return a new template if the chain
+  tip changes or the mempool fees increase above the `MAX_MONEY` threshold.
+  Previously, miners would receive a new template with every request, resulting
+  in unnecessary template generation. This change aligns with the [Stratum
+  V2][topic pooled mining] protocol specification.
+
+- [Eclair #3037][] enhances the `listoffers` command (See Newsletter
+  [#345][news345 offers]) to return all relevant [offer][topic offers] data,
+  including the `createdAt` and `disabledAt` timestamps, instead of just raw
+  Type-Length-Value (TLV) data. In addition, this PR fixes a bug that caused the
+  node to crash when attempting to register the same offer twice.
+
+- [LND #9546][] adds an `ip_range` flag to the `lncli constrainmacaroon` (see
+  Newsletter [#201][news201 constrain]) subcommand, allowing users to restrict
+  access to a resource to a specific IP range when using a macaroon
+  (authentication token). Previously, macaroons could only allow or deny access
+  based on specific IP addresses, not ranges.
+
+- [LND #9458][] introduces restricted access slots for certain peers,
+  configurable via the `--num-restricted-slots` flag, to manage initial access
+  permissions on the server. Peers are assigned access levels based on their
+  channel history: those with a confirmed channel receive protected access,
+  those with an unconfirmed channel receive temporary access, and all others are
+  given restricted access.
+
+- [BTCPay Server #6581][] adds [RBF][topic rbf] support, enabling fee bumping
+  for transactions that have no descendants, where all inputs are from the
+  store’s wallet, and which include one of the store’s change addresses. Users
+  can now choose between [CPFP][topic cpfp] and RBF when choosing to fee bump a
+  transaction. Fee bumping requires NBXplorer version 2.5.22 or higher.
+
+- [BDK #1839][] adds support for detecting and handling canceled (double-spent)
+  transactions by introducing a new `TxUpdate::evicted_ats` field, which updates
+  the `last_evicted` timestamps in `TxGraph`. Transactions are considered
+  evicted if their `last_evicted` timestamp exceeds their `last_seen` timestamp.
+  The canonicalization algorithm (see Newsletter [#335][news335 algorithm]) is
+  updated to ignore evicted transactions except when a canonical descendant
+  exists due to rules of transitivity.
+
+- [BOLTs #1233][] updates a node’s behavior to never fail an [HTLC][topic htlc]
+  upstream if the node knows the preimage, ensuring that the HTLC can be
+  properly settled. Previously, the recommendation was to fail an outstanding
+  HTLC upstream if it was missing from a confirmed commitment, even if the
+  preimage was known. A bug in LND versions before 0.18 caused nodes under DoS
+  attack to fail HTLCs upstream after a restart, despite knowing the preimage,
+  resulting in the loss of the HTLC’s value (see Newsletter [#344][news344
+  lnd]).
+
+{% include snippets/recap-ad.md when="2025-03-25 15:30" %}
+{% include references.md %}
+{% include linkers/issues.md v=2 issues="31649,31283,3037,9546,9458,6581,1839,1233" %}
+[bitcoin core 29.0rc2]: https://bitcoincore.org/bin/bitcoin-core-29.0/
+[morehouse sweep]: https://delvingbitcoin.org/t/lnds-deadline-aware-budget-sweeper/1512
+[ismail sweep]: https://delvingbitcoin.org/t/lnds-deadline-aware-budget-sweeper/1512/3
+[news216 presync]: /en/newsletters/2022/09/07/#bitcoin-core-25717
+[news345 offers]: /en/newsletters/2025/03/14/#eclair-2976
+[news201 constrain]: /en/newsletters/2022/05/25/#lnd-6529
+[news344 lnd]: /en/newsletters/2025/03/07/#disclosure-of-fixed-lnd-vulnerability-allowing-theft
+[news335 algorithm]: /en/newsletters/2025/01/03/#bdk-1670
+[wally 1.4.0]: https://github.com/ElementsProject/libwally-core/releases/tag/release_1.4.0
+[bccg github]: https://github.com/jurraca/core-config-tui
+[riap github]: https://github.com/thunderbiscuit/regtest-in-a-pod
+[podman website]: https://podman.io/
+[podman bitcoin blog]: https://thunderbiscuit.com/posts/podman-bitcoin/
+[explora github]: https://github.com/lontivero/explora
+[hashpool github]: https://github.com/vnprc/hashpool
+[news247 sri]: /en/newsletters/2023/04/19/#stratum-v2-reference-implementation-update-announced
+[pod337 hashpool]: /en/podcast/2025/01/21/#continued-discussion-about-rewarding-pool-miners-with-tradeable-ecash-shares-transcript
+[news281 demand]: /en/newsletters/2023/12/13/#stratum-v2-mining-pool-launches
+[dmnd website]: https://www.dmnd.work/
+[embit website]: https://embit.rocks/
+[news273 krux]: /en/newsletters/2023/10/18/#krux-signing-device-firmware
+[tropic01 website]: https://tropicsquare.com/tropic01
+[tropicsquare github]: https://github.com/tropicsquare
+[nunchuk blog]: https://nunchuk.io/blog/group-wallet
+[frostr github]: https://github.com/FROSTR-ORG
+[new325 bark]: /en/newsletters/2024/10/18/#bark-ark-implementation-announced
+[second blog]: https://blog.second.tech/try-ark-on-signet/
+[cove wallet github]: https://github.com/bitcoinppl/cove

_topics/en/ark.md

@@ -36,6 +36,9 @@ optech_mentions:
   - title: "Ark Wallet SDK released"
     url: /en/newsletters/2025/02/21/#ark-wallet-sdk-released
 
+  - title: "Bark implementation of Ark is now available on signet"
+    url: /en/newsletters/2025/03/21/#bark-launches-on-signet
+
 ## Optional.  Same format as "primary_sources" above
 see_also:
   - title: Joinpools

_topics/en/ecash.md

@@ -44,6 +44,9 @@ optech_mentions:
   - title: "Continued discussion about rewarding pool miners with tradeable ecash shares"
     url: /en/newsletters/2025/01/17/#continued-discussion-about-rewarding-pool-miners-with-tradeable-ecash-shares
 
+  - title: "Hashpool 0.1 tagged based on the Stratum v2 reference implementation with ecash-based shares"
+    url: /en/newsletters/2025/03/21/#hashpool-v0-1-tagged
+
 ## Optional.  Same format as "primary_sources" above
 # see_also:
 #   - title:

_topics/en/fee-estimation.md

@@ -59,6 +59,9 @@ optech_mentions:
   - title: "LDK #3268 adds a more conservative fee estimation method for dust calculations"
     url: /en/newsletters/2024/09/06/#ldk-3268
 
+  - title: "Updated LND sweeper subsystem using multiple feerate estimation methods"
+    url: /en/newsletters/2025/03/21/#discussion-of-lnd-s-dynamic-feerate-adjustment-system
+
 ## Optional.  Same format as "primary_sources" above
 see_also:
   - title: Coin selection

_topics/en/htlc.md

@@ -99,6 +99,9 @@ optech_mentions:
   - title: "LDK #3556 proactively fails HTLCs backwards near expiration even before upstream confirmation"
     url: /en/newsletters/2025/02/07/#ldk-3556
 
+  - title: "BOLTs #1233 adds recommendation to never fail an HTLC upstream if the node knows the preimage"
+    url: /en/newsletters/2025/03/21/#bolts-1233
+
 ## Optional.  Same format as "primary_sources" above
 see_also:
   - title: Hash Time Locked Contracts from Bitcoin Wiki

_topics/en/pooled-mining.md

@@ -86,6 +86,12 @@ optech_mentions:
   - title: "Deterministic transaction selection from a committed mempool for Braidpool decentralized mining"
     url: /en/newsletters/2025/02/07/#deterministic-transaction-selection-from-a-committed-mempool
 
+  - title: "Hashpool 0.1 tagged based on the Stratum v2 reference implementation with ecash-based shares"
+    url: /en/newsletters/2025/03/21/#hashpool-v0-1-tagged
+
+  - title: "DMND pool launches Stratum v2 pooled mining"
+    url: /en/newsletters/2025/03/21/#dmnd-launching-pooled-mining
+
 ## Optional.  Same format as "primary_sources" above
 #see_also:
 #  - title:

_topics/en/replace-by-fee.md

@@ -201,6 +201,9 @@ optech_mentions:
   - title: "Bitcoin Core #30592 removes the `mempoolfullrbf` setting"
     url: /en/newsletters/2024/11/15/#bitcoin-core-30592
 
+  - title: "Updated LND sweeper subsystem for choosing appropriate RBF feerates"
+    url: /en/newsletters/2025/03/21/#discussion-of-lnd-s-dynamic-feerate-adjustment-system
+
 ## Optional.  Same format as "primary_sources" above
 see_also:
   - title: Transaction pinning

_topics/en/replacement-cycling.md

@@ -38,6 +38,9 @@ optech_mentions:
   - title: "Variant of replacement cycling attack that could benefit exploitative miners"
     url: /en/newsletters/2025/01/31/#replacement-cycling-attacks-with-miner-exploitation
 
+  - title: "Updated LND sweeper subsystem for fee bumping to improve replacement cycling resistance"
+    url: /en/newsletters/2025/03/21/#discussion-of-lnd-s-dynamic-feerate-adjustment-system
+
 ## Optional.  Same format as "primary_sources" above
 see_also:
   - title: Transaction replacement

_topics/en/threshold-signature.md

@@ -61,6 +61,9 @@ optech_mentions:
   - title: "Updated ChillDKG draft for distributed key generation for FROST"
     url: /en/newsletters/2025/01/03/#updated-chilldkg-draft
 
+  - title: "FROSTR library for k-of-n signing and key management on nostr"
+    url: /en/newsletters/2025/03/21/#frostr-protocol-announced
+
 ## Optional.  Same format as "primary_sources" above
 see_also:
   - title: Scriptless multisignature

_topics/en/transaction-pinning.md

@@ -93,6 +93,9 @@ optech_mentions:
   - title: "LDK #3340 introduces batching of on-chain claim transactions with pinnable outputs"
     url: /en/newsletters/2025/01/03/#ldk-3340
 
+  - title: "Updated LND sweeper subsystem for fee bumping to improve transaction pinning resistance"
+    url: /en/newsletters/2025/03/21/#discussion-of-lnd-s-dynamic-feerate-adjustment-system
+
 ## Optional.  Same format as "primary_sources" above
 see_also:
    - title: CPFP carve out