Introduce ReceiveAuthKey verification for Blinded Payment Paths by shaavan · Pull Request #4126 · lightningdevkit/rust-lightning

shaavan · 2025-09-25T11:52:08Z

Building on the goals set forth in #3917, this PR introduces ReceiveAuthKey-based verification for Blinded Payment Paths.

Key Outcomes

Uniform verification mechanism: Both payment and message blinded paths now share the same authentication logic.
Smaller payloads: The final ReceiveTlvs are noticeably reduced in size, making blinded paths lighter.

Follow-Up Preparation

This PR also lays the groundwork for introducing dummy payment hops in a follow-up PR.
By minimizing per-hop authentication data, we keep dummy hops compact — preserving overall path size and ensuring that forward and dummy TLVs are padded to the same length, improving hop indistinguishability and privacy.

ldk-reviews-bot · 2025-09-25T11:52:11Z

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codecov · 2025-09-25T12:21:07Z

Codecov Report

❌ Patch coverage is 89.65517% with 12 lines in your changes missing coverage. Please review.
✅ Project coverage is 89.33%. Comparing base (95c4eaf) to head (b18ccb3).
⚠️ Report is 35 commits behind head on main.

Files with missing lines	Patch %	Lines
lightning/src/blinded_path/payment.rs	70.37%	3 Missing and 5 partials ⚠️
lightning/src/routing/router.rs	70.00%	3 Missing ⚠️
lightning/src/ln/msgs.rs	94.11%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4126      +/-   ##
==========================================
+ Coverage   89.28%   89.33%   +0.04%     
==========================================
  Files         180      180              
  Lines      137913   138086     +173     
  Branches   137913   138086     +173     
==========================================
+ Hits       123142   123356     +214     
+ Misses      12167    12127      -40     
+ Partials     2604     2603       -1

Flag	Coverage Δ
fuzzing	`35.86% <4.00%> (+2.30%)`	⬆️
tests	`88.70% <89.65%> (+0.01%)`	⬆️

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ldk-reviews-bot · 2025-09-27T12:02:56Z

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shaavan · 2025-10-06T18:13:40Z

Updated from pr4126.01 to pr4126.02 (diff):

Changes:

Various cleanups
Expanded Documentation
Restructured the fails_receive_tlvs_authentication test so that it can properly test the new ReceiveAuthKey based authentication

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lightning/src/ln/channelmanager.rs

lightning/src/ln/onion_utils.rs

lightning/src/blinded_path/payment.rs

lightning/src/offers/signer.rs

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shaavan · 2025-11-04T11:07:02Z

Updated .02 → .03

Thanks @jkczyz - changes:

Test cleanups
Various documentation changes.

shaavan · 2025-11-04T15:21:52Z

Rebased .03 → .04

shaavan · 2025-11-08T13:14:39Z

Rebased .04 → .05

TheBlueMatt

Thanks!

lightning/src/blinded_path/payment.rs

lightning/src/ln/msgs.rs

lightning/src/offers/signer.rs

shaavan · 2025-11-12T15:15:39Z

Updated .05 → .06

Thanks @TheBlueMatt — changes:

Added used_aad check in decrypt_intro_payload
Restored HMAC variable names for clarity on reuse risk
Moved used_aad check to read-time to simplify downstream logic

jkczyz

LGTM. Mostly some nits but one is needed to be addressed to fix CI.

lightning/src/ln/onion_payment.rs

lightning/src/ln/channelmanager.rs

lightning/src/blinded_path/payment.rs

shaavan · 2025-11-12T18:23:43Z

Updated: .06 → .07

Thanks @jkczyz — changes:

Removed unrelated edits from onion_payment.rs
Fix lint errors
Rename receive_auth_key → local_node_receive_key (match message.rs)
Doc nits

lightning/src/routing/router.rs

lightning/src/ln/onion_utils.rs

Extends the work started in [PR#3917](lightningdevkit#3917) by adding ReceiveAuthKey-based verification for Blinded Payment Paths. This reduces space previously taken by individual ReceiveTlvs and aligns the verification logic with that used for Blinded Message Paths.

Now that we have introduced an alternate mechanism for authentication in the codebase, we can safely remove the now redundant (hmac, nonce) fields from the Payment ReceiveTlvs's while maintaining the security of the onion messages.

shaavan · 2025-11-13T11:11:44Z

Updated: .07 → .08

Thanks @jkczyz — changes:

Removed now redundant LocalHTLCFailureReason variant.
Minor documentation fixes.

TheBlueMatt

Hell yea net code removal!

shaavan force-pushed the aad-payment branch from 69c57f9 to 359267e Compare September 25, 2025 11:58

ldk-reviews-bot requested a review from jkczyz September 25, 2025 12:02

shaavan force-pushed the aad-payment branch from 359267e to 13c4041 Compare September 25, 2025 12:07

shaavan force-pushed the aad-payment branch from 13c4041 to a93113c Compare October 6, 2025 18:13

shaavan mentioned this pull request Oct 9, 2025

Introduce Dummy Hop support for Blinded Payment Path #4152

Merged

jkczyz reviewed Oct 27, 2025

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shaavan force-pushed the aad-payment branch from a93113c to e60f085 Compare November 4, 2025 11:06

shaavan force-pushed the aad-payment branch 2 times, most recently from acbadec to 18e6b33 Compare November 4, 2025 15:21

shaavan force-pushed the aad-payment branch from 18e6b33 to ee46e45 Compare November 8, 2025 13:14

TheBlueMatt reviewed Nov 11, 2025

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shaavan force-pushed the aad-payment branch from ee46e45 to 516c6f5 Compare November 12, 2025 15:15

jkczyz reviewed Nov 12, 2025

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shaavan force-pushed the aad-payment branch from 516c6f5 to a6719b1 Compare November 12, 2025 18:23

jkczyz reviewed Nov 12, 2025

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shaavan force-pushed the aad-payment branch from a6719b1 to 2077a7a Compare November 13, 2025 11:06

shaavan added 2 commits November 13, 2025 16:38

Cleanup: Remove redundant (hmac, nonce) from codebase

b18ccb3

Now that we have introduced an alternate mechanism for authentication in the codebase, we can safely remove the now redundant (hmac, nonce) fields from the Payment ReceiveTlvs's while maintaining the security of the onion messages.

shaavan force-pushed the aad-payment branch from 2077a7a to b18ccb3 Compare November 13, 2025 11:11

jkczyz approved these changes Nov 13, 2025

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shaavan requested a review from TheBlueMatt November 14, 2025 09:29

TheBlueMatt approved these changes Nov 14, 2025

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TheBlueMatt merged commit 6d0254c into lightningdevkit:main Nov 14, 2025
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shaavan commented Sep 25, 2025

Key Outcomes

Follow-Up Preparation

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