On Mon, Jul 20, 2015 at 4:55 PM, Gregory Maxwell <gmaxwell@gmail.com> wrote:

On Mon, Jul 20, 2015 at 7:10 PM, Gavin Andresen via bitcoin-dev
<bitcoin-dev@lists.linuxfoundation.org> wrote:
> Mitigate a potential CPU exhaustion denial-of-service attack by limiting
> the maximum size of a transaction included in a block.

This seems like a fairly indirect approach. The resource being watched
for is not the size (otherwise two transactions for 200k would be
strictly worse than one 200k transactions) but the potential of N^2
costs related to repeated hashing in checksig; which this ignores.

Yes.  The tradeoff is implementation complexity: it is trivial to check transaction size,

not as trivial to count signature operations, because number-of-bytes-in-transaction

doesn't require any context.

But I would REALLY hate myself if in ten years a future version of me was struggling to

get consensus to move away from some stupid 100,000 byte transaction size limit

I imposed to mitigate a potential DoS attack.

So I agree, a limit on sigops is the right way to go. And if that is being changed,

might as well accurately count exactly how many sigops a transaction actually

requires to be validated...

--

--
Gavin Andresen

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