BIP394: rawtr() Output Script Descriptors

bip-rawtr.mediawiki

@@ -0,0 +1,104 @@
+<pre>
+  BIP: ?
+  Layer: Applications
+  Title: rawtr() Output Script Descriptors
+  Authors: jeanpablojp <me@jeanpablo.jp>
+  Status: Draft
+  Type: Informational
+  Assigned: ?
+  License: BSD-2-Clause
+  Discussion: 2026-03-02: https://github.com/bitcoin/bips/pull/2050#issuecomment-3986205616
+              2026-08-06: https://groups.google.com/g/bitcoindev/c/CCZN_qQ5C1s
+  Requires: 341, 380
+</pre>
+
+==Abstract==
+
+This document specifies <tt>rawtr()</tt> output script descriptors.
+A <tt>rawtr()</tt> descriptor expresses a Pay-to-Taproot output by its output key directly, without stating an internal key or a script tree.
+
+==Motivation==
+
+A taproot output key is derived from an internal key and an optional script tree, as described in [[bip-0341.mediawiki|BIP 341]].
+The <tt>tr()</tt> descriptor specified in [[bip-0386.mediawiki|BIP 386]] takes the internal key and the tree, and computes the output key from them.
+There is no way to use <tt>tr()</tt> for an output whose internal structure isn't known, for example an output key received from another party, or one whose script tree the holder does not wish to reveal.
+The <tt>rawtr()</tt> descriptor covers that case by taking the output key itself.
+
+This expression has been implemented in Bitcoin Core since version 24.0, and [[bip-0390.mediawiki|BIP 390]] permits <tt>musig()</tt> inside <tt>rawtr()</tt> and uses it in its test vectors.
+This document gives the expression a specification of its own.
+
+==Specification==
+
+A new script expression is defined: <tt>rawtr()</tt>.
+
+The <tt>rawtr(KEY)</tt> expression can only be used as a top level descriptor.
+It takes a single key expression as an argument and produces a P2TR output script.
+Unlike <tt>tr()</tt>, it does not take a tree expression, and the key is used directly as the taproot output key, with no [[bip-0341.mediawiki|BIP 341]] tweak applied.
+
+The output script produced is:
+<pre>
+OP_1 <KEY>
+</pre>
+
+Key expressions within a <tt>rawtr()</tt> expression must only create x-only public keys, as in <tt>tr()</tt> expressions.
+Uncompressed public keys are not allowed, but compressed public keys would be implicitly converted to x-only public keys.
+The keys derived from extended keys must be serialized as x-only public keys.
+
+If the private key corresponding to the output key is known, the output can be spent via the key path.
+Note that a <tt>rawtr()</tt> descriptor cannot show whether a script path exists for the output: nothing in it proves that the output key does not commit to a script tree.
+Software importing a <tt>rawtr()</tt> descriptor from an untrusted source should warn that other spending paths may exist.
+
+==Test Vectors==
+
+Valid descriptors followed by the scripts they produce. Descriptors involving derived child keys will have the 0th, 1st, and 2nd scripts listed. These vectors were generated with Bitcoin Core's descriptor implementation. Note that the first vector uses the same key as the first <tt>tr()</tt> vector of [[bip-0386.mediawiki|BIP 386]]: with <tt>rawtr()</tt> the key appears in the script unchanged, while <tt>tr()</tt> tweaks it. The third vector takes the output key that the BIP 386 vector produced and reproduces its script.
+
+* <tt>rawtr(a34b99f22c790c4e36b2b3c2c35a36db06226e41c692fc82b8b56ac1c540c5bd)</tt>
+** <tt>5120a34b99f22c790c4e36b2b3c2c35a36db06226e41c692fc82b8b56ac1c540c5bd</tt>
+* <tt>rawtr(L4rK1yDtCWekvXuE6oXD9jCYfFNV2cWRpVuPLBcCU2z8TrisoyY1)</tt>
+** <tt>5120a34b99f22c790c4e36b2b3c2c35a36db06226e41c692fc82b8b56ac1c540c5bd</tt>
+* <tt>rawtr(77aab6e066f8a7419c5ab714c12c67d25007ed55a43cadcacb4d7a970a093f11)</tt>
+** <tt>512077aab6e066f8a7419c5ab714c12c67d25007ed55a43cadcacb4d7a970a093f11</tt>
+* <tt>rawtr(xprvA1RpRA33e1JQ7ifknakTFpgNXPmW2YvmhqLQYMmrj4xJXXWYpDPS3xz7iAxn8L39njGVyuoseXzU6rcxFLJ8HFsTjSyQbLYnMpCqE2VbFWc/0/*)</tt>
+** <tt>51208145454b87fc9ec3557478d6eadc2aea290b50f3c469b828abeb542ae8f8849d</tt>
+** <tt>5120377ad06450813b5f7e10bc94b8b662513398c2d83086f8e67349a00909a5a5a4</tt>
+** <tt>51200a862a965e930b917327d4d08e6309aeb6a4fb0970e133c8ea0d034de04cc3b0</tt>
+* <tt>rawtr(xprvA1RpRA33e1JQ7ifknakTFpgNXPmW2YvmhqLQYMmrj4xJXXWYpDPS3xz7iAxn8L39njGVyuoseXzU6rcxFLJ8HFsTjSyQbLYnMpCqE2VbFWc/<0;1>/*)</tt>, a multipath descriptor as specified in [[bip-0389.mediawiki|BIP 389]], expanding into two descriptors:
+** <tt>rawtr(xpub6ERApfZwUNrhLCkDtcHTcxd75RbzS1ed54G1LkBUHQVHQKqhMkhgbmJbZRkrgZw4koxb5JaHWkY4ALHY2grBGRjaDMzQLcgJvLJuZZvRcEL/0/*)</tt>
+*** <tt>51208145454b87fc9ec3557478d6eadc2aea290b50f3c469b828abeb542ae8f8849d</tt>
+*** <tt>5120377ad06450813b5f7e10bc94b8b662513398c2d83086f8e67349a00909a5a5a4</tt>
+*** <tt>51200a862a965e930b917327d4d08e6309aeb6a4fb0970e133c8ea0d034de04cc3b0</tt>
+** <tt>rawtr(xpub6ERApfZwUNrhLCkDtcHTcxd75RbzS1ed54G1LkBUHQVHQKqhMkhgbmJbZRkrgZw4koxb5JaHWkY4ALHY2grBGRjaDMzQLcgJvLJuZZvRcEL/1/*)</tt>
+*** <tt>5120095e95d8c50ae3f3fea93fa8e983f710489f60ff681a658c06eba64622c824b1</tt>
+*** <tt>51207512d6bd74e24eeb1ad752d5be800adc5886ded11c5293a9a701db83658b526a</tt>
+*** <tt>5120cc9fd211dc0a1c8bb7a106ff831be0e253bc992f21d08fb8a6fd43fae51b9b89</tt>
+* <tt>rawtr(musig(KwDiBf89QgGbjEhKnhXJuH7LrciVrZi3qYjgd9M7rFU74sHUHy8S,03dff1d77f2a671c5f36183726db2341be58feae1da2deced843240f7b502ba659,023590a94e768f8e1815c2f24b4d80a8e3149316c3518ce7b7ad338368d038ca66))</tt>, from the [[bip-0390.mediawiki|BIP 390]] test vectors
+** <tt>5120789d937bade6673538f3e28d8368dda4d0512f94da44cf477a505716d26a1575</tt>
+* <tt>rawtr(musig(xpub6ERApfZwUNrhLCkDtcHTcxd75RbzS1ed54G1LkBUHQVHQKqhMkhgbmJbZRkrgZw4koxb5JaHWkY4ALHY2grBGRjaDMzQLcgJvLJuZZvRcEL,xpub68NZiKmJWnxxS6aaHmn81bvJeTESw724CRDs6HbuccFQN9Ku14VQrADWgqbhhTHBaohPX4CjNLf9fq9MYo6oDaPPLPxSb7gwQN3ih19Zm4Y)/0/*)</tt>, from the [[bip-0390.mediawiki|BIP 390]] test vectors
+** <tt>51209508c08832f3bb9d5e8baf8cb5cfa3669902e2f2da19acea63ff47b93faa9bfc</tt>
+** <tt>51205ca1102663025a83dd9b5dbc214762c5a6309af00d48167d2d6483808525a298</tt>
+** <tt>51207dbed1b89c338df6a1ae137f133a19cae6e03d481196ee6f1a5c7d1aeb56b166</tt>
+
+Invalid Descriptors
+
+* <tt>rawtr()</tt> nested in <tt>sh</tt>: <tt>sh(rawtr(a34b99f22c790c4e36b2b3c2c35a36db06226e41c692fc82b8b56ac1c540c5bd))</tt>
+* <tt>rawtr()</tt> nested in <tt>wsh</tt>: <tt>wsh(rawtr(a34b99f22c790c4e36b2b3c2c35a36db06226e41c692fc82b8b56ac1c540c5bd))</tt>
+* Script expression instead of a key expression: <tt>rawtr(pk(a34b99f22c790c4e36b2b3c2c35a36db06226e41c692fc82b8b56ac1c540c5bd))</tt>
+* More than one key: <tt>rawtr(a34b99f22c790c4e36b2b3c2c35a36db06226e41c692fc82b8b56ac1c540c5bd,77aab6e066f8a7419c5ab714c12c67d25007ed55a43cadcacb4d7a970a093f11)</tt>
+* Tree expression, which <tt>rawtr()</tt> does not take: <tt>rawtr(a34b99f22c790c4e36b2b3c2c35a36db06226e41c692fc82b8b56ac1c540c5bd,pk(77aab6e066f8a7419c5ab714c12c67d25007ed55a43cadcacb4d7a970a093f11))</tt>
+* Uncompressed private key: <tt>rawtr(5KYZdUEo39z3FPrtuX2QbbwGnNP5zTd7yyr2SC1j299sBCnWjss)</tt>
+* Uncompressed public key: <tt>rawtr(04a34b99f22c790c4e36b2b3c2c35a36db06226e41c692fc82b8b56ac1c540c5bd5b8dec5235a0fa8722476c7709c02559e3aa73aa03918ba2d492eea75abea235)</tt>
+* No key: <tt>rawtr()</tt>
+
+==Backwards Compatibility==
+
+<tt>rawtr()</tt> descriptors use the format and general operation specified in [[bip-0380.mediawiki|380]].
+This is a wholly new descriptor, and as such is not compatible with any implementation that predates it.
+The scripts produced are standard Pay-to-Taproot scripts, so existing software is likely to be familiar with them.
+
+==Reference Implementation==
+
+<tt>rawtr()</tt> descriptors have been implemented in Bitcoin Core since version 24.0.
+
+==Copyright==
+
+This BIP is licensed under the BSD 2-clause license.