pub unsafe extern "C" fn chachapoly_auth_decrypt(
    ctx: *mut chachapoly_context,
    length: size_t,
    nonce: *const c_uchar,
    aad: *const c_uchar,
    aad_len: size_t,
    tag: *const c_uchar,
    input: *const c_uchar,
    output: *mut c_uchar
) -> c_int