rich1.0Nadav Kohen [ARCHIVE] (npub1ge…rtua0)https://yabu.me/npub1geqdlge6ysz9qlq3w758422flnkgqklpu9veu80ehjprcd04ugyqkrtua0njumphttps://yabu.me📅 Original date posted:2020-04-22 📝 Original message: Hello all, I'd like to give an update on the current state of thinking and coding surrounding replacing Hash-TimeLock Contracts (HTLCs) with Point-TimeLock Contracts (PTLCs) (aka Payment Hashes -> Payment Points) in hopes of sparking interest, discussion, development, etc. We Want Payment Points! ----------------------- Using point-locks (in PTLCs) instead of hash-locks (in HTLCs) for lightning payments is an all around improvement. HTLCs require the use of the same hash across payment routes (barring fancy ZKPs which are inferior to PTLCs) while PTLCs allow for payment de-correlation along routes. For an introduction to the topic, see https://suredbits.com/payment-points-part-1/. In addition to improving privacy in this way and protecting against wormhole attacks, PTLC-based lightning channels open the door to a large variety of interesting applications that cannot be accomplished with HTLCs: Stuckless (retry-able) Payments with proof of payment ( https://suredbits.com/payment-points-part-2-stuckless-payments/) Escrow contracts over Lightning ( https://suredbits.com/payment-points-part-3-escrow-contracts/) High/DLOG AMP ( https://docs.google.com/presentation/d/15l4h2_zEY4zXC6n1NqsImcjgA0fovl_lkgkKu1O3QT0/edit#slide=id.g64c15419e7_0_40 ) Stuckless + AMP (an improvement on Boomerang) ( https://lists.linuxfoundation.org/pipermail/lightning-dev/2019-October/002239.html ) Pay-for-signature ( https://suredbits.com/payment-points-part-4-selling-signatures/) Pay-for-commitment ( https://lists.linuxfoundation.org/pipermail/lightning-dev/2019-September/002166.html ) Monotonic access structures on payment completion ( https://suredbits.com/payment-points-monotone-access-structures/) Ideal Barrier Escrow Implementation ( https://suredbits.com/payment-points-implementing-barrier-escrows/) And allowing for Barrier Escrows, we can even have Atomic multi-payment setup ( https://suredbits.com/payment-points-and-barrier-escrows/) Lightning Discreet Log Contract ( https://suredbits.com/discreet-log-contracts-on-lightning-network/) Atomic multi-payment update ( https://suredbits.com/updating-and-transferring-lightning-payments/) Lightning Discreet Log Contract Novation/Transfer ( https://suredbits.com/transferring-lightning-dlcs/) There are likely even more things that can be done with Payment Points so make sure to respond if I've missed any known ones. How Do We Get Payment Points? ----------------------------- Eventually, once we have Taproot, we can use 2p-Schnorr adaptor signatures in Lightning channels. For a detailed thread by ZmnSCPxj, see here https://lists.linuxfoundation.org/pipermail/lightning-dev/2019-December/002375.html In the meantime, Lloyd has written about a way to do 1p-ECDSA adaptor sigs ( https://github.com/LLFourn/one-time-VES) which can be paired with OP_CHECKMULTISIG to allows us to execute PTLCs on Bitcoin today! Nickler has implemented this in a branch of secp256k1 ( https://github.com/jonasnick/secp256k1/pull/14) and I have implemented it in Bouncy Castle in Bitcoin-S with some testing against this branch ( https://github.com/nkohen/bitcoin-s-core/tree/bouncy-adaptor). Do note that as nickler states on his PR, "IT IS EXTREMELY DANGEROUS AND RECKLESS TO USE THIS MODULE IN PRODUCTION. DON'T!" A demo of an on-chain PTLC I executed using nickler's implementation on the backend + bitcoin-s can be seen here https://youtu.be/w9o4v7Idjno And waxwing did a lovely write-up about the crypto itself https://joinmarket.me/blog/blog/schnorrless-scriptless-scripts/ I would be very interested in having a fork of (at least) one lightning implementation (or Rust Lightning) to be a proof of concept ECDSA-PTLC node with which we can test and play with the plethora of PTLC-based proposals above. I believe this would only require a few changes to existing nodes: 1) update_add_ptlc will have a 32 byte x-coordinate (of a point) rather than a 32 byte hash. Additionally the onion's hop_data will contain a 32 byte scalar tweak for each hop. As per [link multi-hop locks]. The last hop_data will instead include a 32 byte scalar equal to the sum of all tweaks. 2) commitment_signed will have 162 byte adaptor ptlc_signatures rather than valid (71/72 byte) ECDSA signatures on PTLC-success transactions. 3) The in-flight outputs on the commitment transaction itself become a little simpler as we no longer need to explicitly check the payment pre-image against a hash. Instead, delete all instances of "OP_HASH160 <RIPEMD160(payment_hash)> OP_EQUALVERIFY" in the scripts (leaving the rest the same) and require no pre-image in the witness, only a valid signature. The pre-image check is implicitly enforced by the <remoteptlc_sig> witness since only an adaptor signature was provided by remote so that the payment pre-image is required to create the valid signature (from which the pre-image can be then deduced by comparing adaptor and valid signatures). If I've missed any other changes that need to happen, do respond with them! I hope that as a community we can work towards having a PTLC-based Lightning Network that is safe and stable as soon as possible, and so I encourage further thinking, development and expirementation with PTLCs now so that when Taproot is finally at our disposal we can cleanly start moving towards a more ideal Lightning :) Best, Nadav -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.linuxfoundation.org/pipermail/lightning-dev/attachments/20200422/a0197f12/attachment.html>