Subject: Re: [bitcoin-dev] Script Abuse Potential?

From: Jorge Timón <[email-masked]>
Date: Wed, 4 Jan 2017 15:45:54 +0100

I would assume that the controversial part of op_cat comes from the fact
that it enables covenants. Are there more concerns than that?

On 4 Jan 2017 04:14, "Russell O'Connor via bitcoin-dev" <
[email-masked]> wrote:

> For the record, the OP_CAT limit of 520 bytes was added by Satoshi
> <https://github.com/bitcoin/bitcoin/commit/4bd188c4383d6e614e18f79dc337fbabe8464c82#diff-8458adcedc17d046942185cb709ff5c3R425>
> on the famous August 15, 2010 "misc" commit, at the same time that OP_CAT
> was disabled.
> The previous limit was 5000 bytes.
>
> On Tue, Jan 3, 2017 at 7:13 PM, Jeremy via bitcoin-dev <bitcoin-dev@lists.
> linuxfoundation.org> wrote:
>
>> Sure, was just upper bounding it anyways. Even less of a problem!
>>
>>
>> RE: OP_CAT, not as OP_CAT was specified, which is why it was disabled. As
>> far as I know, the elements alpha proposal to reenable a limited op_cat to
>> 520 bytes is somewhat controversial...
>>
>>
>>
>> --
>> @JeremyRubin <https://twitter.com/JeremyRubin>
>> <https://twitter.com/JeremyRubin>
>>
>> On Mon, Jan 2, 2017 at 10:39 PM, Johnson Lau <[email-masked]> wrote:
>>
>>> No, there could only have not more than 201 opcodes in a script. So you
>>> may have 198 OP_2DUP at most, i.e. 198 * 520 * 2 = 206kB
>>>
>>> For OP_CAT, just check if the returned item is within the 520 bytes
>>> limit.
>>>
>>> On 3 Jan 2017, at 11:27, Jeremy via bitcoin-dev <
>>> [email-masked]> wrote:
>>>
>>> It is an unfortunate script, but can't actually
>>> ​do
>>>  that much
>>> ​ it seems​
>>> . The MAX_SCRIPT_ELEMENT_SIZE = 520 Bytes.
>>> ​ Thus, it would seem the worst you could do with this would be to (10000-520*2)*520*2
>>> bytes  ~=~ 10 MB.
>>>
>>> ​Much more concerning would be the op_dup/op_cat style bug, which under
>>> a similar script ​would certainly cause out of memory errors :)
>>>
>>>
>>>
>>> --
>>> @JeremyRubin <https://twitter.com/JeremyRubin>
>>> <https://twitter.com/JeremyRubin>
>>>
>>> On Mon, Jan 2, 2017 at 4:39 PM, Steve Davis via bitcoin-dev <
>>> [email-masked]> wrote:
>>>
>>>> Hi all,
>>>>
>>>> Suppose someone were to use the following pk_script:
>>>>
>>>> [op_2dup, op_2dup, op_2dup, op_2dup, op_2dup, ...(to limit)...,
>>>> op_2dup, op_hash160, <addr_hash>, op_equalverify, op_checksig]
>>>>
>>>> This still seems to be valid AFAICS, and may be a potential attack
>>>> vector?
>>>>
>>>> Thanks.
>>>>
>>>>
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>>
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