Make signing follow BIP340 exactly w.r.t. aux randomness

libsecp256k1's secp256k1_schnorrsig_sign only follows BIP340 exactly
if an aux_rand32 argument is passed. When no randomness is used
(as is the case in the current codebase here), there is no impact
on security between not providing aux_rand32 at all, or providing
an empty one. Yet, for repeatability/testability it is simpler
to always use an all-zero one.

1 files changed, 2 insertions, 2 deletions

diff --git a/src/key.h b/src/key.h
index af8d2e72d8..eab18b284a 100644
--- a/src/key.h
+++ b/src/key.h
@@ -130,7 +130,7 @@ public:
 
     /**
      * Create a BIP-340 Schnorr signature, for the xonly-pubkey corresponding to *this,
-     * optionally tweaked by *merkle_root. Additional nonce entropy can be provided through
+     * optionally tweaked by *merkle_root. Additional nonce entropy is provided through
      * aux.
      *
      * merkle_root is used to optionally perform tweaking of the private key, as specified
@@ -143,7 +143,7 @@ public:
      *                              (this is used for key path spending, with specific
      *                              Merkle root of the script tree).
      */
-    bool SignSchnorr(const uint256& hash, Span<unsigned char> sig, const uint256* merkle_root = nullptr, const uint256* aux = nullptr) const;
+    bool SignSchnorr(const uint256& hash, Span<unsigned char> sig, const uint256* merkle_root, const uint256& aux) const;
 
     //! Derive BIP32 child key.
     bool Derive(CKey& keyChild, ChainCode &ccChild, unsigned int nChild, const ChainCode& cc) const;