Merge bitcoin/bitcoin#32642: test: update BIP340 test vectors and implementation (variable-length messages)

b184f5c test: update BIP340 test vectors and implementation (variable-length messages) (Sebastian Falbesoner)

Pull request description:

  This PR updates the Schnorr signatures implementation in the functional test framework to the latest BIP changes (see bitcoin/bips#1446 200f9b26fe0a2f235a2af8b30c4be9f12f6bc9cb) and syncs the [test vectors](https://github.com/bitcoin/bips/blob/master/bip-0340/test-vectors.csv) accordingly. Practically, we probably don't need non-32-bytes message signing/verifying any time soon, but it seems good practice anyways to update.

ACKs for top commit:
  stratospher:
    ACK b184f5c.
  achow101:
    ACK b184f5c
  real-or-random:
    utACK b184f5c
  jonasnick:
    utACK b184f5c

Tree-SHA512: b566823aa0f1cd7151215178c57551d772b338d022ccb2807a0df2670df6d59c4b63a6fc936708ccf2922c7e59f474f544adaafc4aea731bfd896250c0d45fa6

Author: achow101

test/functional/test_framework/bip340_test_vectors.csv

@@ -14,3 +14,7 @@ index,secret key,public key,aux_rand,message,signature,verification result,comme
 12,,DFF1D77F2A671C5F36183726DB2341BE58FEAE1DA2DECED843240F7B502BA659,,243F6A8885A308D313198A2E03707344A4093822299F31D0082EFA98EC4E6C89,FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFEFFFFFC2F69E89B4C5564D00349106B8497785DD7D1D713A8AE82B32FA79D5F7FC407D39B,FALSE,sig[0:32] is equal to field size
 13,,DFF1D77F2A671C5F36183726DB2341BE58FEAE1DA2DECED843240F7B502BA659,,243F6A8885A308D313198A2E03707344A4093822299F31D0082EFA98EC4E6C89,6CFF5C3BA86C69EA4B7376F31A9BCB4F74C1976089B2D9963DA2E5543E177769FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFEBAAEDCE6AF48A03BBFD25E8CD0364141,FALSE,sig[32:64] is equal to curve order
 14,,FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFEFFFFFC30,,243F6A8885A308D313198A2E03707344A4093822299F31D0082EFA98EC4E6C89,6CFF5C3BA86C69EA4B7376F31A9BCB4F74C1976089B2D9963DA2E5543E17776969E89B4C5564D00349106B8497785DD7D1D713A8AE82B32FA79D5F7FC407D39B,FALSE,public key is not a valid X coordinate because it exceeds the field size
+15,0340034003400340034003400340034003400340034003400340034003400340,778CAA53B4393AC467774D09497A87224BF9FAB6F6E68B23086497324D6FD117,0000000000000000000000000000000000000000000000000000000000000000,,71535DB165ECD9FBBC046E5FFAEA61186BB6AD436732FCCC25291A55895464CF6069CE26BF03466228F19A3A62DB8A649F2D560FAC652827D1AF0574E427AB63,TRUE,message of size 0 (added 2022-12)
+16,0340034003400340034003400340034003400340034003400340034003400340,778CAA53B4393AC467774D09497A87224BF9FAB6F6E68B23086497324D6FD117,0000000000000000000000000000000000000000000000000000000000000000,11,08A20A0AFEF64124649232E0693C583AB1B9934AE63B4C3511F3AE1134C6A303EA3173BFEA6683BD101FA5AA5DBC1996FE7CACFC5A577D33EC14564CEC2BACBF,TRUE,message of size 1 (added 2022-12)
+17,0340034003400340034003400340034003400340034003400340034003400340,778CAA53B4393AC467774D09497A87224BF9FAB6F6E68B23086497324D6FD117,0000000000000000000000000000000000000000000000000000000000000000,0102030405060708090A0B0C0D0E0F1011,5130F39A4059B43BC7CAC09A19ECE52B5D8699D1A71E3C52DA9AFDB6B50AC370C4A482B77BF960F8681540E25B6771ECE1E5A37FD80E5A51897C5566A97EA5A5,TRUE,message of size 17 (added 2022-12)
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message of size 100 (added 2022-12)

test/functional/test_framework/key.py

@@ -242,10 +242,9 @@ def verify_schnorr(key, sig, msg):
 
     - key is a 32-byte xonly pubkey (computed using compute_xonly_pubkey).
     - sig is a 64-byte Schnorr signature
-    - msg is a 32-byte message
+    - msg is a variable-length message
     """
     assert len(key) == 32
-    assert len(msg) == 32
     assert len(sig) == 64
 
     P = secp256k1.GE.from_bytes_xonly(key)
@@ -272,7 +271,6 @@ def sign_schnorr(key, msg, aux=None, flip_p=False, flip_r=False):
         aux = bytes(32)
 
     assert len(key) == 32
-    assert len(msg) == 32
     assert len(aux) == 32
 
     sec = int.from_bytes(key, 'big')