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Comment by halJordan | Hacker News Reader

Idk you lost me when you said using two schemes is not more complex than using one scheme. That doing two things at once is more complex than doing one is just not an axiom I'm willing to give up. And if you're willing to then i have to guess it's for ideological reasons than rational or logical ones. So at that point we're not analyzing the opinions of an expert organization we're just blasting cynicism at the "bad guy."

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This sentence also bothered me, however, later in the text he says that of course there's a complexity cost, but that he believes the costs are quite low. I think one can reasonably argue that.

One sentence with unfortunately chosen words shouldn't invalidate the - in my view largely reasonable - arguments of the whole text.

I don't believe the claim was that it adds no complexity, but was saying it adds no complexity due to the reasons mentioned. He then goes on to write a paragraph about why that is the case, which you could of course respond to.

To add more, we are talking about a hybrid scheme that uses both a post-quantum algorithm and a classical algorithm, where the former is much slower than the later and a mere hybrid doesn't make much difference in performance. And this scheme will be presented as a single choice in cryptographic protocols, so if the protocol already supports multiple cryptosystems it should be just fine to adopt.

DJB also explains needs for hybrids as follows: we don't yet have any post-quantum algorithm that we can confidently use as a direct substitute for well-established classical algorithms. So for now we need to consider possibilities for QC becoming real and PQ algorithms broken, hence hybrids.

You might have read that wrong. The article acknowledges the added complexity:

> "hybrid solutions make implementations even more complex".

> If the words are taken purely at face value then they're clearly correct

The argument here is that the complexity is mostly due to the adding of new algorithm, not the hybridization. It goes on to argue that the added complexity due to the hybridization itself is negligible, especially considering the level of security provided.

Doing 2 things is more complex than 1, but doing 1 new and much more complex thing in addition to 1 old much simpler and already verified thing has very little complexity over omitting the old thing and doing just the new one.

In both cases the work is in adding and testing the new thing.

Whether you comment out or not the old thing does not really change the amount of programmer work and the execution time and required resources are also not affected significantly in this case.

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