pub unsafe extern "C" fn rsa_gen_key(
    ctx: *mut rsa_context,
    f_rng: Option<unsafe extern "C" fn(arg1: *mut c_void, arg2: *mut c_uchar, arg3: size_t) -> c_int>,
    p_rng: *mut c_void,
    nbits: c_uint,
    exponent: c_int
) -> c_int