For the record, the OP_CAT limit of 520 bytes was added by Satoshi 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...On Mon, Jan 2, 2017 at 10:39 PM, Johnson Lau <jl2012@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 = 206kBFor 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 actuallydothat 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 :)______________________________
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.
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