rich1.0npub1g5zswf6y48f7fy90jf3tlcuwdmjn8znhzaa4vkmtxaeskca8hpss23ms3lhttps://nostr.ae/npub1g5zswf6y48f7fy90jf3tlcuwdmjn8znhzaa4vkmtxaeskca8hpss23ms3lnjumphttps://nostr.ae📅 Original date posted:2019-10-04 📝 Original message:Good morning Jeremy, > Awhile back, Ethan and I discussed having, rather than OP_CAT, an OP_SHA256STREAM that uses the streaming properties of a SHA256 hash function to allow concatenation of an unlimited amount of data, provided the only use is to hash it. > > You can then use it perhaps as follows: > > // start a new hash with item > OP_SHA256STREAM  (-1) -> [state] > // Add item to the hash in state > OP_SHA256STREAM n [item] [state] -> [state] > // Finalize > OP_SHA256STREAM (-2) [state] -> [Hash] > > <-1> OP_SHA256STREAM <tag> <subnode 2> <subnode 3> <3> OP_SHA256STREAM <-2> OP_SHA256STREAM > > Or it coul > This seems a good idea. Though it brings up the age-old tension between: * Generically-useable components, but due to generalization are less efficient. * Specific-use components, which are efficient, but which may end up not being useable in the future. In particular, `OP_SHA256STREAM` would no longer be useable if SHA256 eventually is broken, while the `OP_CAT` will still be useable in the indefinite future. In the future a new hash function can simply be defined and the same technique with `OP_CAT` would still be useable. Regards, ZmnSCPxj > -- > @JeremyRubin > > On Thu, Oct 3, 2019 at 8:04 PM Ethan Heilman <eth3rs at gmail.com> wrote: > > > I hope you are having an great afternoon ZmnSCPxj, > > > > You make an excellent point! > > > > I had thought about doing the following to tag nodes > > > > || means OP_CAT > > > > `node = SHA256(type||SHA256(data))` > > so a subnode would be > > `subnode1 = SHA256(1||SHA256(subnode2||subnode3))` > > and a leaf node would be > > `leafnode = SHA256(0||SHA256(leafdata))` > > > > Yet, I like your idea better. Increasing the size of the two inputs to > > OP_CAT to be 260 Bytes each where 520 Bytes is the maximum allowable > > size of object on the stack seems sensible and also doesn't special > > case the logic of OP_CAT. > > > > It would also increase performance. SHA256(tag||subnode2||subnode3) > > requires 2 compression function calls whereas > > SHA256(1||SHA256(subnode2||subnode3)) requires 2+1=3 compression > > function calls (due to padding). > > > > >Or we could implement tagged SHA256 as a new opcode... > > > > I agree that tagged SHA256 as an op code that would certainty be > > useful, but OP_CAT provides far more utility and is a simpler change. > > > > Thanks, > > Ethan > > > > On Thu, Oct 3, 2019 at 7:42 PM ZmnSCPxj <ZmnSCPxj at protonmail.com> wrote: > > > > > > Good morning Ethan, > > > > > > > > > > To avoid derailing the NO_INPUT conversation, I have changed the > > > > subject to OP_CAT. > > > > > > > > Responding to: > > > > """ > > > > > > > > -   `SIGHASH` flags attached to signatures are a misdesign, sadly > > > >     retained from the original BitCoin 0.1.0 Alpha for Windows design, on > > > >     par with: > > > >     [..] > > > > > > > > -   `OP_CAT` and `OP_MULT` and `OP_ADD` and friends > > > >     [..] > > > >     """ > > > > > > > >     OP_CAT is an extremely valuable op code. I understand why it was > > > >     removed as the situation at the time with scripts was dire. However > > > >     most of the protocols I've wanted to build on Bitcoin run into the > > > >     limitation that stack values can not be concatenated. For instance > > > >     TumbleBit would have far smaller transaction sizes if OP_CAT was > > > >     supported in Bitcoin. If it happens to me as a researcher it is > > > >     probably holding other people back as well. If I could wave a magic > > > >     wand and turn on one of the disabled op codes it would be OP_CAT. Of > > > >     course with the change that size of each concatenated value must be 64 > > > >     Bytes or less. > > > > > > Why 64 bytes in particular? > > > > > > It seems obvious to me that this 64 bytes is most suited for building Merkle trees, being the size of two SHA256 hashes. > > > > > > However we have had issues with the use of Merkle trees in Bitcoin blocks. > > > Specifically, it is difficult to determine if a hash on a Merkle node is the hash of a Merkle subnode, or a leaf transaction. > > > My understanding is that this is the reason for now requiring transactions to be at least 80 bytes. > > > > > > The obvious fix would be to prepend the type of the hashed object, i.e. add at least one byte to determine this type. > > > Taproot for example uses tagged hash functions, with a different tag for leaves, and tagged hashes are just prepend-this-32-byte-constant-twice-before-you-SHA256. > > > > > > This seems to indicate that to check merkle tree proofs, an `OP_CAT` with only 64 bytes max output size would not be sufficient. > > > > > > Or we could implement tagged SHA256 as a new opcode... > > > > > > Regards, > > > ZmnSCPxj > > > > > > > > > > > > > >     On Tue, Oct 1, 2019 at 10:04 PM ZmnSCPxj via bitcoin-dev > > > >     bitcoin-dev at lists.linuxfoundation.org wrote: > > > > > > > > > > > > > Good morning lists, > > > > > Let me propose the below radical idea: > > > > > > > > > > -   `SIGHASH` flags attached to signatures are a misdesign, sadly retained from the original BitCoin 0.1.0 Alpha for Windows design, on par with: > > > > >     -   1 RETURN > > > > >     -   higher-`nSequence` replacement > > > > >     -   DER-encoded pubkeys > > > > >     -   unrestricted `scriptPubKey` > > > > >     -   Payee-security-paid-by-payer (i.e. lack of P2SH) > > > > >     -   `OP_CAT` and `OP_MULT` and `OP_ADD` and friends > > > > >     -   transaction malleability > > > > >     -   probably many more > > > > > > > > > > So let me propose the more radical excision, starting with SegWit v1: > > > > > > > > > > -   Remove `SIGHASH` from signatures. > > > > > -   Put `SIGHASH` on public keys. > > > > > > > > > > Public keys are now encoded as either 33-bytes (implicit `SIGHASH_ALL`) or 34-bytes (`SIGHASH` byte, followed by pubkey type, followed by pubkey coordinate). > > > > > `OP_CHECKSIG` and friends then look at the public key to determine sighash algorithm rather than the signature. > > > > > As we expect public keys to be indirectly committed to on every output `scriptPubKey`, this is automatically output tagging to allow particular `SIGHASH`. > > > > > However, we can then utilize the many many ways to hide public keys away until they are needed, exemplified in MAST-inside-Taproot. > > > > > I propose also the addition of the opcode: > > > > > > > > > >     <sighash> <pubkey> OP_SETPUBKEYSIGHASH > > > > > > > > > > > > > > > -   `sighash` must be one byte. > > > > > -   `pubkey` may be the special byte `0x1`, meaning "just use the Taproot internal pubkey". > > > > > -   `pubkey` may be 33-byte public key, in which case the `sighash` byte is just prepended to it. > > > > > -   `pubkey` may be 34-byte public key with sighash, in which case the first byte is replaced with `sighash` byte. > > > > > -   If `sighash` is `0x00` then the result is a 33-byte public key (the sighash byte is removed) i.e. `SIGHASH_ALL` implicit. > > > > > > > > > > This retains the old feature where the sighash is selected at time-of-spending rather than time-of-payment. > > > > > This is done by using the script: > > > > > > > > > >     <pubkey> OP_SETPUBKEYSIGHASH OP_CHECKSIG > > > > > > > > > > > > > > > Then the sighash can be put in the witness stack after the signature, letting the `SIGHASH` flag be selected at time-of-signing, but only if the SCRIPT specifically is formed to do so. > > > > > This is malleability-safe as the signature still commits to the `SIGHASH` it was created for. > > > > > However, by default, public keys will not have an attached `SIGHASH` byte, implying `SIGHASH_ALL` (and disallowing-by-default non-`SIGHASH_ALL`). > > > > > This removes the problems with `SIGHASH_NONE` `SIGHASH_SINGLE`, as they are allowed only if the output specifically says they are allowed. > > > > > Would this not be a superior solution? > > > > > Regards, > > > > > ZmnSCPxj > > > > > > > > > > bitcoin-dev mailing list > > > > > bitcoin-dev at lists.linuxfoundation.org > > > > > https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev > > > > > > > > Lightning-dev mailing list > > > > Lightning-dev at lists.linuxfoundation.org > > > > https://lists.linuxfoundation.org/mailman/listinfo/lightning-dev > > > > > > > > _______________________________________________ > > Lightning-dev mailing list > > Lightning-dev at lists.linuxfoundation.org > > https://lists.linuxfoundation.org/mailman/listinfo/lightning-dev