public inbox for bitcoindev@googlegroups.com
 help / color / mirror / Atom feed
From: Steven Roose <steven@roose.io>
To: vjudeu via bitcoin-dev <bitcoin-dev@lists.linuxfoundation.org>
Subject: Re: [bitcoin-dev] Proposed BIP for OP_CAT
Date: Tue, 24 Oct 2023 20:47:23 +0100	[thread overview]
Message-ID: <c76d5c5f-091a-8c41-f1e7-74774c9607c5@roose.io> (raw)
In-Reply-To: <194372901-852eeb9299035adb7fdfc7fe5aa21080@pmq3v.m5r2.onet>

[-- Attachment #1: Type: text/plain, Size: 7441 bytes --]

I agree that there is no reason not to use OP_SUCCESS126, i.e. the 
original OP_CAT opcode 0x7e. In many codebases, for example in Core, 
there might be two OP_CAT constants than which might be confusing.

On 10/22/23 09:58, vjudeu via bitcoin-dev wrote:
> > This opcode would be activated via a soft fork by redefining the 
> opcode OP_SUCCESS80.
> Why OP_SUCCESS80, and not OP_SUCCESS126? When there is some existing 
> opcode, it should be reused. And if OP_RESERVED will ever be 
> re-enabled, I think it should behave in the same way, as in 
> pre-Taproot, so it should "Mark transaction as invalid unless occuring 
> in an unexecuted OP_IF branch". Which means, "<condition> OP_VERIFY" 
> should be equivalent to "<condition> OP_NOTIF OP_RESERVED OP_ENDIF".
>
>
> On 2023-10-21 07:09:13 user Ethan Heilman via bitcoin-dev 
> <bitcoin-dev@lists.linuxfoundation.org> wrote:
>
>     Hi everyone,
>
>     We've posted a draft BIP to propose enabling OP_CAT as Tapscript opcode.
>     https://github.com/EthanHeilman/op_cat_draft/blob/main/cat.mediawiki
>
>     OP_CAT was available in early versions of Bitcoin. It was disabled as
>     it allowed the construction of a script whose evaluation could create
>     stack elements exponential in the size of the script. This is no
>     longer an issue in the current age as tapscript enforces a maximum
>     stack element size of 520 Bytes.
>
>     Thanks,
>     Ethan
>
>     ==Abstract==
>
>     This BIP defines OP_CAT a new tapscript opcode which allows the
>     concatenation of two values on the stack. This opcode would be
>     activated via a soft fork by redefining the opcode OP_SUCCESS80.
>
>     When evaluated the OP_CAT instruction:
>     # Pops the top two values off the stack,
>     # concatenate the popped values together,
>     # and then pushes the concatenated value on the top of the stack.
>
>     OP_CAT fails if there are less than two values on the stack or if a
>     concatenated value would have a combined size of greater than the
>     maximum script element size of 520 Bytes.
>
>     ==Motivation==
>     Bitcoin tapscript lacks a general purpose way of combining objects on
>     the stack restricting the expressiveness and power of tapscript. For
>     instance this prevents among many other things the ability to
>     construct and evaluate merkle trees and other hashed data structures
>     in tapscript. OP_CAT by adding a general purpose way to concatenate
>     stack values would overcome this limitation and greatly increase the
>     functionality of tapscript.
>
>     OP_CAT aims to expand the toolbox of the tapscript developer with a
>     simple, modular and useful opcode in the spirit of Unix[1]. To
>     demonstrate the usefulness of OP_CAT below we provide a non-exhaustive
>     list of some usecases that OP_CAT would enable:
>
>     * Tree Signatures provide a multisignature script whose size can be
>     logarithmic in the number of public keys and can encode spend
>     conditions beyond n-of-m. For instance a transaction less than 1KB in
>     size could support tree signatures with a thousand public keys. This
>     also enables generalized logical spend conditions. [2]
>     * Post-Quantum Lamport Signatures in Bitcoin transactions. Lamport
>     signatures merely requires the ability to hash and concatenate values
>     on the stack. [3]
>     * Non-equivocation contracts [4] in tapscript provide a mechanism to
>     punish equivocation/double spending in Bitcoin payment channels.
>     OP_CAT enables this by enforcing rules on the spending transaction's
>     nonce. The capability is a useful building block for payment channels
>     and other Bitcoin protocols.
>     * Vaults [5] which are a specialized covenant that allows a user to
>     block a malicious party who has compromised the user's secret key from
>     stealing the funds in that output. As shown in A. Poelstra, "CAT
>     and Schnorr Tricks II", 2021,
>     https://www.wpsoftware.net/andrew/blog/cat-and-schnorr-tricks-ii.html
>     OP_CAT is sufficent to build vaults in Bitcoin.
>     * Replicating CheckSigFromStack  A. Poelstra, "CAT and Schnorr
>     Tricks I", 2021,
>     https://medium.com/blockstream/cat-and-schnorr-tricks-i-faf1b59bd298
>       which would allow the creation of simple covenants and other
>     advanced contracts without having to presign spending transactions,
>     possibly reducing complexity and the amount of data that needs to be
>     stored. Originally shown to work with Schnorr signatures, this result
>     has been extended to ECDSA signatures. [6]
>
>     The opcode OP_CAT was available in early versions of Bitcoin. However
>     OP_CAT was removed because it enabled the construction of a script for
>     which an evaluation could have memory usage exponential in the size of
>     the script.
>     For instance a script which pushed an 1 Byte value on the stack then
>     repeated the opcodes OP_DUP, OP_CAT 40 times would result in a stack
>     value whose size was greater than 1 Terabyte. This is no longer an
>     issue because tapscript enforces a maximum stack element size of 520
>     Bytes.
>
>     ==Specification==
>
>     Implementation
>
>        if (stack.size() < 2)
>          return set_error(serror, SCRIPT_ERR_INVALID_STACK_OPERATION);
>        valtype vch1 = stacktop(-2);
>        valtype vch2 = stacktop(-1);
>
>        if (vch1.size() + vch2.size() > MAX_SCRIPT_ELEMENT_SIZE)
>            return set_error(serror, SCRIPT_ERR_INVALID_STACK_OPERATION);
>
>        valtype vch3;
>        vch3.reserve(vch1.size() + vch2.size());
>        vch3.insert(vch3.end(), vch1.begin(), vch1.end());
>        vch3.insert(vch3.end(), vch2.begin(), vch2.end());
>
>        popstack(stack);
>        popstack(stack);
>        stack.push_back(vch3);
>
>     The value of MAX_SCRIPT_ELEMENT_SIZE is 520 Bytes == Reference Implementation == [Elements](https://github.com/ElementsProject/elements/blob/master/src/script/interpreter.cpp#L1043) ==References== [1]: R. Pike and B. Kernighan, "Program design in the UNIX environment", 1983,https://harmful.cat-v.org/cat-v/unix_prog_design.pdf  [2]: P. Wuille, "Multisig on steroids using tree signatures", 2015,https://lists.linuxfoundation.org/pipermail/bitcoin-dev/2021-July/019233.html  [3]: J. Rubin, "[bitcoin-dev] OP_CAT Makes Bitcoin Quantum Secure [was CheckSigFromStack for Arithmetic Values]", 2021,https://lists.linuxfoundation.org/pipermail/bitcoin-dev/2021-July/019233.html  [4]: T. Ruffing, A. Kate, D. Schröder, "Liar, Liar, Coins on Fire: Penalizing Equivocation by Loss of Bitcoins", 2015,https://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.727.6262&rep=rep1&type=pdf  [5]: M. Moser, I. Eyal, and E. G. Sirer, Bitcoin Covenants,http://fc16.ifca.ai/bitcoin/papers/MES16.pdf  [6]: R. Linus, "Covenants with CAT and ECDSA", 2023,https://gist.github.com/RobinLinus/9a69f5552be94d13170ec79bf34d5e85#file-covenants_cat_ecdsa-md  _______________________________________________ bitcoin-dev mailing listbitcoin-dev@lists.linuxfoundation.org  https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev
>
>
> _______________________________________________
> bitcoin-dev mailing list
> bitcoin-dev@lists.linuxfoundation.org
> https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev

[-- Attachment #2: Type: text/html, Size: 9532 bytes --]

  reply	other threads:[~2023-10-24 19:47 UTC|newest]

Thread overview: 20+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-10-21  5:08 [bitcoin-dev] Proposed BIP for OP_CAT Ethan Heilman
2023-10-21  5:49 ` alicexbt
2023-10-21 15:03 ` Andrew Poelstra
2023-10-26 16:04   ` James O'Beirne
2023-10-21 16:10 ` Greg Sanders
2023-10-21 20:24   ` Ethan Heilman
2023-10-22  8:58 ` vjudeu
2023-10-24 19:47   ` Steven Roose [this message]
2023-10-26  1:53     ` Ethan Heilman
2023-10-23  2:13 ` Rusty Russell
2023-10-23 12:26   ` Anthony Towns
2023-10-23 13:41   ` Andrew Poelstra
2023-10-24  0:48     ` Rusty Russell
2023-10-24  1:17       ` Andrew Poelstra
2023-10-24  3:45         ` Rusty Russell
2023-10-24 13:05           ` Andrew Poelstra
2023-10-26 21:55 ` Peter Todd
2023-10-27 18:32 ` Anthony Towns
2023-10-23  5:13 vjudeu
2023-10-26 14:30 ` Ryan Grant

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=c76d5c5f-091a-8c41-f1e7-74774c9607c5@roose.io \
    --to=steven@roose.io \
    --cc=bitcoin-dev@lists.linuxfoundation.org \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox