Type Definition secp256k1_sys::SchnorrNonceFn

pub type SchnorrNonceFn = Option<unsafe extern "C" fn(nonce32: *mut c_uchar, msg32: *const c_uchar, msg_len: size_t, key32: *const c_uchar, xonly_pk32: *const c_uchar, algo16: *const c_uchar, algo_len: size_t, data: *mut c_void) -> c_int>;

Same as secp256k1_nonce function with the exception of accepting an additional pubkey argument and not requiring an attempt argument. The pubkey argument can protect signature schemes with key-prefixed challenge hash inputs against reusing the nonce when signing with the wrong precomputed pubkey.