Merge bitcoin/bitcoin#29154: tests: improve wallet multisig descriptor test and docs

d93b79470916b1e6f85c55cc6beb1e41b382196f tests: improve wallet multisig descriptor test and docs (Michael Dietz)

Pull request description:

  It is best to store all key origin information
  (master key fingerprint and all derivation steps)
  in the multisig descriptor. Being explicit with
  this information should be beneficial if this approach is used with other wallets/signers (whether hardware or software). There is no harm including all of this with xpubs (if anything it simplifies the test code) and makes this example/docs more complete and safer incase it is referenced by others.

ACKs for top commit:
  S3RK:
    Code Review ACK d93b79470916b1e6f85c55cc6beb1e41b382196f
  achow101:
    ACK d93b79470916b1e6f85c55cc6beb1e41b382196f

Tree-SHA512: 0e5c4d13f060489405e6cf50c8a09911f5a0cee71023649235afd80a5e3aae38d52c6e12ad4660205b9357b09f45596941391bdcf6fceccbe07c4e5a1592a482

1 files changed, 3 insertions, 2 deletions

diff --git a/doc/descriptors.md b/doc/descriptors.md
index 3b94ec03e4..5e8e4a24b0 100644
--- a/doc/descriptors.md
+++ b/doc/descriptors.md
@@ -63,6 +63,7 @@ Output descriptors currently support:
 - `wsh(sortedmulti(1,xpub661MyMwAqRbcFW31YEwpkMuc5THy2PSt5bDMsktWQcFF8syAmRUapSCGu8ED9W6oDMSgv6Zz8idoc4a6mr8BDzTJY47LJhkJ8UB7WEGuduB/1/0/*,xpub69H7F5d8KSRgmmdJg2KhpAK8SR3DjMwAdkxj3ZuxV27CprR9LgpeyGmXUbC6wb7ERfvrnKZjXoUmmDznezpbZb7ap6r1D3tgFxHmwMkQTPH/0/0/*))` describes a set of *1-of-2* P2WSH multisig outputs where one multisig key is the *1/0/`i`* child of the first specified xpub and the other multisig key is the *0/0/`i`* child of the second specified xpub, and `i` is any number in a configurable range (`0-1000` by default). The order of public keys in the resulting witnessScripts is determined by the lexicographic order of the public keys at that index.
 - `tr(c6047f9441ed7d6d3045406e95c07cd85c778e4b8cef3ca7abac09b95c709ee5,{pk(fff97bd5755eeea420453a14355235d382f6472f8568a18b2f057a1460297556),pk(e493dbf1c10d80f3581e4904930b1404cc6c13900ee0758474fa94abe8c4cd13)})` describes a P2TR output with the `c6...` x-only pubkey as internal key, and two script paths.
 - `tr(c6047f9441ed7d6d3045406e95c07cd85c778e4b8cef3ca7abac09b95c709ee5,sortedmulti_a(2,2f8bde4d1a07209355b4a7250a5c5128e88b84bddc619ab7cba8d569b240efe4,5cbdf0646e5db4eaa398f365f2ea7a0e3d419b7e0330e39ce92bddedcac4f9bc))` describes a P2TR output with the `c6...` x-only pubkey as internal key, and a single `multi_a` script that needs 2 signatures with 2 specified x-only keys, which will be sorted lexicographically.
+- `wsh(sortedmulti(2,[6f53d49c/44h/1h/0h]tpubDDjsCRDQ9YzyaAq9rspCfq8RZFrWoBpYnLxK6sS2hS2yukqSczgcYiur8Scx4Hd5AZatxTuzMtJQJhchufv1FRFanLqUP7JHwusSSpfcEp2/0/*,[e6807791/44h/1h/0h]tpubDDAfvogaaAxaFJ6c15ht7Tq6ZmiqFYfrSmZsHu7tHXBgnjMZSHAeHSwhvjARNA6Qybon4ksPksjRbPDVp7yXA1KjTjSd5x18KHqbppnXP1s/0/*,[367c9cfa/44h/1h/0h]tpubDDtPnSgWYk8dDnaDwnof4ehcnjuL5VoUt1eW2MoAed1grPHuXPDnkX1fWMvXfcz3NqFxPbhqNZ3QBdYjLz2hABeM9Z2oqMR1Gt2HHYDoCgh/0/*))#av0kxgw0` describes a *2-of-3* multisig. For brevity, the internal "change" descriptor accompanying the above external "receiving" descriptor is not included here, but it typically differs only in the xpub derivation steps, ending in `/1/*` for change addresses.
 
 ## Reference
 
@@ -167,9 +168,9 @@ The basic steps are:
      the participant's signer wallet. Avoid reusing this wallet for any purpose other than signing transactions from the
      corresponding multisig we are about to create. Hint: extract the wallet's xpubs using `listdescriptors` and pick the one from the
      `pkh` descriptor since it's least likely to be accidentally reused (legacy addresses)
-  2. Create a watch-only descriptor wallet (blank, private keys disabled). Now the multisig is created by importing the two descriptors:
+  2. Create a watch-only descriptor wallet (blank, private keys disabled). Now the multisig is created by importing the external and internal descriptors:
      `wsh(sortedmulti(<M>,XPUB1/0/*,XPUB2/0/*,…,XPUBN/0/*))` and `wsh(sortedmulti(<M>,XPUB1/1/*,XPUB2/1/*,…,XPUBN/1/*))`
-     (one descriptor w/ `0` for receiving addresses and another w/ `1` for change). Every participant does this
+     (one descriptor w/ `0` for receiving addresses and another w/ `1` for change). Every participant does this. All key origin information (master key fingerprint and all derivation steps) should be included with xpubs for proper support of hardware devices / external signers
   3. A receiving address is generated for the multisig. As a check to ensure step 2 was done correctly, every participant
      should verify they get the same addresses
   4. Funds are sent to the resulting address