I meant we could use four 64-bit numbers to represent 256 bits. Regarding the long way until 512-bit keys will be needed - I want to implement RSA with 4096 bits.
Edit: Not everyone has hardware with AVX support, why not 128 bits at least/most?
It is well-known that RSA needs much longer keys to achieve the same crypto strength. Ethereum uses ECC, and I was talking about ECC, so it is not clear why RSA is relevant here (or ROT13, for that matter).