BIP341: SigHash: Clarify SIGHASH_DEFAULT

Author: reardencode

bip-0341.mediawiki

@@ -90,7 +90,7 @@ We first define a reusable common signature message calculation function, follow
 
 The function ''SigMsg(hash_type, ext_flag)'' computes the message being signed as a byte array. It is implicitly also a function of the spending transaction and the outputs it spends, but these are not listed to keep notation simple.
 
-The parameter ''hash_type'' is an 8-bit unsigned value. The <code>SIGHASH</code> encodings from the legacy script system are reused, including <code>SIGHASH_ALL</code>, <code>SIGHASH_NONE</code>, <code>SIGHASH_SINGLE</code>, and <code>SIGHASH_ANYONECANPAY</code>, plus the default ''hash_type'' value ''0x00'' which results in signing over the whole transaction just as for <code>SIGHASH_ALL</code>. The following restrictions apply, which cause validation failure if violated:
+The parameter ''hash_type'' is an 8-bit unsigned value. The <code>SIGHASH</code> encodings from the legacy script system are reused, including <code>SIGHASH_ALL</code>, <code>SIGHASH_NONE</code>, <code>SIGHASH_SINGLE</code>, and <code>SIGHASH_ANYONECANPAY</code>. We define a new ''hashtype'' <code>SIGHASH_DEFAULT</code> (value ''0x00'') which results in signing over the whole transaction just as for <code>SIGHASH_ALL</code>. The following restrictions apply, which cause validation failure if violated:
 * Using any undefined ''hash_type'' (not ''0x00'', ''0x01'', ''0x02'', ''0x03'', ''0x81'', ''0x82'', or ''0x83''<ref>'''Why reject unknown ''hash_type'' values?''' By doing so, it is easier to reason about the worst case amount of signature hashing an implementation with adequate caching must perform.</ref>).
 * Using <code>SIGHASH_SINGLE</code> without a "corresponding output" (an output with the same index as the input being verified).