Merge bitcoin/bitcoin#23383: Update libsecp256k1 subtree to current master

314195c8be3bd7db0d5817c4fb3aa85c84363ce9 Remove unnecessary cast in CKey::SignSchnorr (Pieter Wuille)
a1f76cdb22e3278a48d63dd23c1fe3308daedd8c Remove --disable-openssl-tests for libsecp256k1 configure (Pieter Wuille)
86dbc4d075decb82fbba837aaa283cf0561897ad Squashed 'src/secp256k1/' changes from be8d9c262f..0559fc6e41 (Pieter Wuille)

Pull request description:

  The motivation for this bump is getting rid of a cast in `CKey::SignSchnorr`; the `aux_rand` argument isn't modified by the `secp256k1_schnorrsig_sign` function, but was marked as non-`const` anyway. This is fixed now (bitcoin-core/secp256k1#966), and the cast is removed in this PR.

  There are a few other relevant changes:
  * (bitcoin-core/secp256k1#956): replaces a runtime-computed table with a precomputed one; this adds arouns 1 MiB to the binary size, but is a step towards significantly simplifying the API. If 1 MiB is too much, it can be reduced by 2 or 4 (or more) for a slight verification performance reduction.
  * (bitcoin-core/secp256k1#983): removes (test/bench only) OpenSSL support entirely, removing the need to pass `--disable-openssl-tests` (see #23314).
  * (bitcoin-core/secp256k1#810): mild performance increase for 64-bit non-x86 platforms.
  * (bitcoin-core/secp256k1#1002): Make aux_rnd32==NULL behave identical to 0x0000..00 (which impacts BIP341/BIP342 signing in Bitcoin Core, making it more strictly BIP340 compliant, though not in a manner that affects security).

ACKs for top commit:
  fanquake:
    ACK 314195c8be3bd7db0d5817c4fb3aa85c84363ce9 - this includes a nice simplification to the lilbsecp build system (and thus our build system), and fixes issues like #22854. Did a Guix build on x86 (above), as well as a build on arm64 (except for the arm64 host):

Tree-SHA512: 0e048390fc148fbbdf5b98d9cce8c71067564e7d69d97b68347808a9bc45a04f4fc653c392c880d79d5d8b9cf282195520955581ac4f1595f6a948080cf5949d

1 files changed, 8 insertions, 7 deletions

diff --git a/src/secp256k1/include/secp256k1_schnorrsig.h b/src/secp256k1/include/secp256k1_schnorrsig.h
index 74cbcac45e..e971ddc2aa 100644
--- a/src/secp256k1/include/secp256k1_schnorrsig.h
+++ b/src/secp256k1/include/secp256k1_schnorrsig.h
@@ -106,12 +106,13 @@ typedef struct {
  *  signatures from being valid in multiple contexts by accident.
  *
  *  Returns 1 on success, 0 on failure.
- *  Args:    ctx: pointer to a context object, initialized for signing (cannot be NULL)
- *  Out:   sig64: pointer to a 64-byte array to store the serialized signature (cannot be NULL)
- *  In:    msg32: the 32-byte message being signed (cannot be NULL)
- *       keypair: pointer to an initialized keypair (cannot be NULL)
+ *  Args:    ctx: pointer to a context object, initialized for signing.
+ *  Out:   sig64: pointer to a 64-byte array to store the serialized signature.
+ *  In:    msg32: the 32-byte message being signed.
+ *       keypair: pointer to an initialized keypair.
  *    aux_rand32: 32 bytes of fresh randomness. While recommended to provide
- *                this, it is only supplemental to security and can be NULL. See
+ *                this, it is only supplemental to security and can be NULL. A
+ *                NULL argument is treated the same as an all-zero one. See
  *                BIP-340 "Default Signing" for a full explanation of this
  *                argument and for guidance if randomness is expensive.
  */
@@ -120,7 +121,7 @@ SECP256K1_API int secp256k1_schnorrsig_sign(
     unsigned char *sig64,
     const unsigned char *msg32,
     const secp256k1_keypair *keypair,
-    unsigned char *aux_rand32
+    const unsigned char *aux_rand32
 ) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2) SECP256K1_ARG_NONNULL(3) SECP256K1_ARG_NONNULL(4);
 
 /** Create a Schnorr signature with a more flexible API.
@@ -150,7 +151,7 @@ SECP256K1_API int secp256k1_schnorrsig_sign_custom(
  *  Returns: 1: correct signature
  *           0: incorrect signature
  *  Args:    ctx: a secp256k1 context object, initialized for verification.
- *  In:    sig64: pointer to the 64-byte signature to verify (cannot be NULL)
+ *  In:    sig64: pointer to the 64-byte signature to verify.
  *           msg: the message being verified. Can only be NULL if msglen is 0.
  *        msglen: length of the message
  *        pubkey: pointer to an x-only public key to verify with (cannot be NULL)