[Simplicity] Simplicity's first transaction

Hi everyone, I'd like to give an update on Simplicity development. We have reached a small milestone last week where we have created and redeemed a Simplicity TXO on an Elements regtest instance. A few weeks ago, we created a simplicity branch on Elements[1] that pulls in the Simplicity project[2] as a subtree and does an experimental integration into Elements. For this experimental development, we created an improper segwit version, "version 31" for Simplicity addresses. The payload of this segwit version 31 address contains a commitment Merkle root of a Simplicity program to control the UTXO. A Simplicity UTXO is redeemed by providing a serialized Simplicity program as the sole element of the segwit witness stack. In order for the transaction to be valid, the provided Simplicity program's commitment Merkle root must match the one in the address, and the Simplicity program must execute without failure. For more details about commitment Merkle roots and the serialization format, see the Simplicity Tech Report[3]. I've posted a gist[4] that illustrates my first Simplicity transaction in Elements regtest. The second output of tx 5f1a02019de32faa3722acaa35524ee2d99ff4d0611763fc02a7e31caf875271 sends ¤1 to the Simplicity segwit address ert1lp3z0u3ur7t8hlfnneh28sn0u0fpwcr6f4zwtk7d4ejzn0994zhusfelwg0. This is the address for a Simplicity commitment Merkle root of 0c44fe4783f2cf7fa673cdd4784dfc7a42ec0f49a89cbb79b5cc853794b515f9, which is the root of the 'CheckSigHashAll' Simplicity program for elements with the public key 0300000000000000000000003b78ce563f89a0ed9414f5aa28ad0d96d6795f9c63 (see [6]). The 'CheckSigHashAll' program creates a custom 'sigAll'[7] transaction digest using the elements specific transaction introspection primitives of Simplicity. The program then requires a Schnorr signature on that digest with the committed public key. The input of tx 33cb976d29e072d64b67b40dda4655f022b1ced1e12ef452884e3e55f2dfc067 redeems this Simplicity UTXO by providing the serialization in the txinwitness field of this Simplicity program along with the required signature. Do not be put off by the 15K in witness data. Discounted jets have not been implemented yet, so the witness includes a complete description of the Schnorr signature verification function written in raw Simplicity. Once discounted jets are in place, that description can be replaced by a handful of bits to denote that specific function. The verification time will also be reduced commensurately with a discounted jet is in place. While I'm very happy with this achievement, there is still much development work ahead. In addition to developing a library of useful jets, we also still need to implement several anti-witness-malleability feature, and anti-DoS features in order to make the implementation suitable for operation on an adversarial network. This includes implementing various resource usage bound and/or costs. Of course, more documentation and tooling surrounding Simplicity is needed as well. The above redemption transaction was essentially hand edited hex with the signature made by doing calculations using an elliptic curve calculator. Moreover this experimental integration into Elements will not be Simplicity's final form. Currently the integration is using an improper segwit version, but this is only out of an abundance of caution. I could switch to a random unused (proper) version of segwit if that is needed for other tool support (perhaps PBST will demand a proper Segwit version). Ultimately Simplicity is going to end up as a tapleaf version[8] rather than a segwit version though. But until we get a taproot implementation in Elements, we will continue to do experimental development using a segwit version. I'll keep everyone updated as we make further progress. [1]https://github.com/ElementsProject/elements/tree/simplicity [2]https://github.com/ElementsProject/simplicity [3]https://github.com/ElementsProject/simplicity/blob/pdf/Simplicity-TR.pdf [4] https://gist.github.com/roconnor-blockstream/2d0c3e340b7f17178984a71786280537 [5] https://github.com/ElementsProject/simplicity/blob/36aaf50eb179e72aad29d7246535ba808909b6f8/Haskell/Simplicity/Elements/Programs/CheckSigHashAll.hs#L112 [6] https://github.com/ElementsProject/simplicity/blob/0db68c5a6dfb7cf54d110f566e20ff1f55098d58/C/primitive/elements/checkSigHashAllTx1.c [7] https://github.com/ElementsProject/simplicity/blob/36aaf50eb179e72aad29d7246535ba808909b6f8/Haskell/Simplicity/Elements/Programs/CheckSigHashAll.hs#L112 [8]https://github.com/sipa/bips/blob/bip-schnorr/bip-taproot.mediawiki -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.ozlabs.org/pipermail/simplicity/attachments/20190917/83ed323f/attachment.htm>