BIP352: Improve input_hash wording #1629

1. 
   josibake commented at 12:30 pm on June 29, 2024: member

   Since #1622, it makes more sense to define input_hash inline, vs having its own section.

   Also remove the wording about txid and vout, since this is already defined in the specification.

2. BIP352: improve input_hash wording

   Since https://github.com/bitcoin/bips/pull/1622, it makes more sense
   to define input_hash inline, vs having its own section.

   8ac84bd344
3. josibake force-pushed on Jun 29, 2024
4. 
   jonatack commented at 2:23 pm on June 29, 2024: contributor

   Pinging @andrewtoth as this addresses https://github.com/bitcoin/bips/pull/1622/files#r1658805198.
5. in bip-0352.mediawiki:300 in 8ac84bd344

   296@@ -303,7 +297,7 @@ After the inputs have been selected, the sender can create one or more outputs f
   297 * For each private key ''a<sub>i</sub>'' corresponding to a [https://github.com/bitcoin/bips/blob/master/bip-0341.mediawiki BIP341] taproot output, check that the private key produces a point with an even Y coordinate and negate the private key if not<ref name="why_negate_taproot_private_keys">'''Why do taproot private keys need to be checked?''' Recall from [https://github.com/bitcoin/bips/blob/master/bip-0340.mediawiki BIP340] that each X-only public key has two corresponding private keys, ''d'' and ''n - d''. To maintain parity between sender and receiver, it is necessary to use the private key corresponding to the even Y coordinate when performing the ECDH step since the receiver will assume the even Y coordinate when summing the taproot X-only public keys.</ref>
   298 * Let ''a = a<sub>1</sub> + a<sub>2</sub> + ... + a<sub>n</sub>'', where each ''a<sub>i</sub>'' has been negated if necessary
   299 ** If ''a = 0'', fail
   300-* Generate the ''input_hash'' with the smallest outpoint lexicographically and ''A = a·G'', using the method described above
   301+* Let ''input_hash = hash<sub>BIP0352/Inputs</sub>(outpoint<sub>L</sub> || A)'', where ''outpoint<sub>L</sub>'' is the smallest ''outpoint'' lexicographically used in the transaction<ref name="why_smallest_outpoint"></ref> and ''A = a·G''
   

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   jonatack commented at 2:26 pm on June 29, 2024:

   A = a·G becomes just A with this change, aligning it with the change https://github.com/bitcoin/bips/pull/1622/files#diff-f675d83bad4bfe13848faf132a4130f2d6801d36c12308854dbf6adcddac8398R102 IIUC?

   Edit: never mind, misread the diff.

6. 
   andrewtoth commented at 2:55 pm on June 29, 2024: contributor

   lgtm ACK 8ac84bd344c2375c4ffc57e65da1527ec191cc5f
7. jonatack merged this on Jun 29, 2024
8. jonatack closed this on Jun 29, 2024

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9. 
   theStack commented at 3:19 pm on June 29, 2024: contributor

   post-merge ACK 8ac84bd344c2375c4ffc57e65da1527ec191cc5f

Contributors
josibake jonatack andrewtoth theStack