[bitcoin-dev] OP_SECURETHEBAG (supersedes OP_CHECKOUTPUTSVERIFY)

[Russell O'Connor]

On Sat, Jun 1, 2019 at 12:47 PM Jeremy via bitcoin-dev <
bitcoin-dev at lists.linuxfoundation.org> wrote:

> Hi All,
>
> OP_CHECKOUTPUTSHASHVERIFY is retracted in favor of OP_SECURETHEBAG*.
> OP_SECURETHEBAG does more or less the same thing, but fixes malleability
> issues and lifts the single output restriction to a known number of inputs
> restriction.
>
> OP_CHECKOUTPUTSVERIFY had some issues with malleability of version and
> locktime. OP_SECURETHEBAG commits to both of these values.
>

Can you elaborate a bit more on what the issues were?


> OP_SECURETHEBAG also lifts the restriction that OP_CHECKOUTPUTSVERIFY had
> to be spent as only a single input, and instead just commits to the number
> of inputs. This allows for more flexibility, but keeps it easy to get the
> same single output restriction.
>
> BIP:
> https://github.com/JeremyRubin/bips/blob/op-secure-the-bag/bip-secure-the-bag.mediawiki
> Implementation: https://github.com/JeremyRubin/bitcoin/tree/secure_the_bag
>
> A particularly useful topic of discussion is how best to eliminate the
> PUSHDATA and treat OP_SECURETHEBAG like a pushdata directly. I thought
> about how the interpreter works and is implemented and couldn't come up
> with something noninvasive.
>

I'm not a Core developer but from what I understand, I'd be inclined to to
treat OP_SECURETHEBAG as with an immediate 32-byte parameter by modifying
GetScriptOp to return the 32-byte parameter through pvchRet.

bool GetScriptOp(CScriptBase::const_iterator& pc,
CScriptBase::const_iterator end, opcodetype& opcodeRet,
std::vector<unsigned char>* pvchRet)
{
    opcodeRet = OP_INVALIDOPCODE;
    if (pvchRet)
        pvchRet->clear();
    if (pc >= end)
        return false;

    // Read instruction
    if (end - pc < 1)
        return false;
    unsigned int opcode = *pc++;

    // Immediate operand
    if (opcode <= OP_PUSHDATA4)
    {
        // ...
    }

    if (opcode == OP_SECURETHEBAG) {
        if (end - pc < 0 || (unsigned int)(end - pc) < 32)
            return false;
        if (pvchRet)
            pvchRet->assign(pc, pc + 32);
        pc += 32;
    }

    opcodeRet = static_cast<opcodetype>(opcode);
    return true;
}

and go from there.

Thank you for your review and discussion,
>
> Jeremy
>
> * Plus the name is better
>
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