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BIP16 has no relation to bip-taproot/tapscript

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Previously did.
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Gregory Sanders 2019-11-11 15:32:57 -05:00 committed by Pieter Wuille
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bip-tapscript.mediawiki
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@ -50,7 +50,7 @@ The rules below only apply when validating a transaction input for which all of
* The leaf version is ''0xc0'' (i.e. the first byte of the last witness element after removing the optional annex is ''0xc0'' or ''0xc1'')<ref>'''How is the ''0xc0'' constant chosen?''' Following the guidelines in bip-taproot, by choosing a value having the two top bits set, tapscript spends are identifiable even without access to the UTXO being spent.</ref>, marking it as a '''tapscript spend'''.
Validation of such inputs must be equivalent to performing the following steps in the specified order.
# If the input is invalid due to BIP16, BIP141, or bip-taproot, fail.
# If the input is invalid due to BIP141 or bip-taproot, fail.
# The script as defined in bip-taproot (i.e., the penultimate witness stack element after removing the optional annex) is called the '''tapscript''' and is decoded into opcodes, one by one:
## If any opcode numbered ''80, 98, 126-129, 131-134, 137-138, 141-142, 149-153, 187-254'' is encountered, validation succeeds (none of the rules below apply). This is true even if later bytes in the tapscript would fail to decode otherwise. These opcodes are renamed to <code>OP_SUCCESS80</code>, ..., <code>OP_SUCCESS254</code>, and collectively known as <code>OP_SUCCESSx</code><ref>'''<code>OP_SUCCESSx</code>''' <code>OP_SUCCESSx</code> is a mechanism to upgrade the Script system. Using an <code>OP_SUCCESSx</code> before its meaning is defined by a softfork is insecure and leads to fund loss. The inclusion of <code>OP_SUCCESSx</code> in a script will pass it unconditionally. It precedes any script execution rules to avoid the difficulties in specifying various edge cases, for example: <code>OP_SUCCESSx</code> in a script with an input stack larger than 1000 elements, <code>OP_SUCCESSx</code> after too many signature opcodes, or even scripts with conditionals lacking <code>OP_ENDIF</code>. The mere existence of an <code>OP_SUCCESSx</code> anywhere in the script will guarantee a pass for all such cases. <code>OP_SUCCESSx</code> are similar to the <code>OP_RETURN</code> in very early bitcoin versions (v0.1 up to and including v0.3.5). The original <code>OP_RETURN</code> terminates script execution immediately, and return pass or fail based on the top stack element at the moment of termination. This was one of a major design flaws in the original bitcoin protocol as it permitted unconditional third party theft by placing an <code>OP_RETURN</code> in <code>scriptSig</code>. This is not a concern in the present proposal since it is not possible for a third party to inject an <code>OP_SUCCESSx</code> to the validation process, as the <code>OP_SUCCESSx</code> is part of the script (and thus committed to be the taproot output), implying the consent of the coin owner. <code>OP_SUCCESSx</code> can be used for a variety of upgrade possibilities:
* An <code>OP_SUCCESSx</code> could be turned into a functional opcode through a softfork. Unlike <code>OP_NOPx</code>-derived opcodes which only have read-only access to the stack, <code>OP_SUCCESSx</code> may also write to the stack. Any rule changes to an <code>OP_SUCCESSx</code>-containing script may only turn a valid script into an invalid one, and this is always achievable with softforks.