descriptors: disallow hybrid public keys

The descriptor documentation (doc/descriptors.md) and BIP380 explicitly
require that hex-encoded public keys start with 02 or 03 (compressed) or
04 (uncompressed). However, the current parsing/inference code permit 06
and 07 (hybrid) encoding as well. Fix this.

1 files changed, 6 insertions, 0 deletions

diff --git a/src/pubkey.h b/src/pubkey.h
index 274779f9a4..4b34fd829b 100644
--- a/src/pubkey.h
+++ b/src/pubkey.h
@@ -191,6 +191,12 @@ public:
         return size() > 0;
     }
 
+    /** Check if a public key is a syntactically valid compressed or uncompressed key. */
+    bool IsValidNonHybrid() const noexcept
+    {
+        return size() > 0 && (vch[0] == 0x02 || vch[0] == 0x03 || vch[0] == 0x04);
+    }
+
     //! fully validate whether this is a valid public key (more expensive than IsValid())
     bool IsFullyValid() const;