I want to critique one particular point made in this article, becuase it’s incorrect:<p><i>> IOTA uses cryptography that cannot be broken by quantum computers. The use of such cryptography, specifically Winternitz signatures, leaves IOTA users vulnerable to loss of funds if they ever reuse an address. This attack that has already been seen in practice, with one user reportedly losing $30,000 USD worth of IOTA.<p>As quantum computers large enough to threaten existing cryptosystems do not exist and may not exist for many decades, this use of post quantum cryptography comes with no tangible benefit.</i><p>“No tangible benefit” is a gross overstatement and simplification. I wholeheartedly agree that 1) novel cryptography should not be adopted before it has been well-studied, and 2) threat models for motivating novel cryptography should be rational and pass a cost-benefit analysis. However, if and when quantum computers can practically break classical cryptosystems, they will be able to do against everything cryptography is used to secure today, not just going forwards. This is a stonger argument for encryption and confidentiality, but it nevertheless also applies to signatures and authentication. As a tangential point: while they aren’t perfect (in terms of efficiency), Winternitz signatures are very well studied. Given what’s available, it’s not a bad choice.<p>I think a lot of IOTA’s specification is pretty suspect, especially since it does utilize novel cryptography without an apparent track record or notable expertise among its team. But I also absolutely believe new cryptocurrencies and blockchain projects should be preparing for quantum computation now, if it’s possible. More pertinently, I don’t agree with the way this point was presented, because it can be interpreted as the claim that post-quantum cryptography is a useful heuristic in determining if a project has “issues”. In reality all cryptography should be suspect, and the use of post-quantum cryptography should not be dismissed immediately as a waste. With IOTA in particular, I’m weakly on the side that they shouldn’t have bothered with Winternitz signatures. But in general, I’m happy to see any project at least giving it serious consideration.