pub unsafe extern "C" fn secp256k1_whitelist_sign(
    ctx: *const Context,
    sig: *mut WhitelistSignature,
    online_keys: *const PublicKey,
    offline_keys: *const PublicKey,
    n_keys: size_t,
    sub_pubkey: *const PublicKey,
    online_seckey: *const c_uchar,
    summed_seckey: *const c_uchar,
    index: size_t
) -> c_int