why n-pushes

Author: instagibbs

bip-0345.mediawiki

@@ -242,7 +242,7 @@ where
 * <code><leaf-update-script-body></code> is a minimally-encoded data push of a serialized script. <ref>In conjunction with the leaf-update data items, it dictates the tapleaf script in the output taptree that will replace the one currently executing.</ref>
 ** Otherwise, script execution MUST fail and terminate immediately.
 
-* <code><n-pushes></code> is an up to 4-byte <code>CScriptNum</code>-encoded number indicating how many leaf-update script items should be popped off the stack.
+* <code><n-pushes></code> is an up to 4-byte <code>CScriptNum</code>-encoded number indicating how many leaf-update script items should be popped off the stack. <ref>'''Why only prepending with data pushes?''' Prepending the <code>leaf-update-script-body</code> with opcodes opens up the door to prepending OP_SUCCESSX opcodes, to name a single issue only, side-stepping the validation that was meant to be run by the committed script.</ref>
 ** If this value does not decode to a valid CScriptNum, script execution when spending this output MUST fail and terminate immediately.
 ** If this value is less than 0, script execution when spending this output MUST fail and terminate immediately.
 ** If fewer than <code><n-pushes> + 2</code> items are on the stack, script execution when spending this output MUST fail and terminate immediately.