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" < bitcoin-dev@lists.linuxfoundation.org> 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 <jl2...@xbt.hk> 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 < >>> bitcoin-dev@lists.linuxfoundation.org> 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 < >>> bitcoin-dev@lists.linuxfoundation.org> 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. >>>> >>>> >>>> _______________________________________________ >>>> bitcoin-dev mailing list >>>> bitcoin-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 >>> >>> >>> >> >> _______________________________________________ >> bitcoin-dev mailing list >> bitcoin-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 > >
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