scrypt: recommending larger values in 2021

[karelbilek]

I have noticed the values kept being from 2017, despite single-core performance getting faster, for example with Apple's ARM M1 offering.

So, I re-tested the N parameter, with the code from here

https://blog.filippo.io/the-scrypt-parameters/

The results, on M1 Macbook Air:

N = 2^14 26ms N = 2^15 53ms N = 2^16 108ms N = 2^17 219ms N = 2^18 441ms N = 2^19 901ms N = 2^20 1778ms N = 2^21 3675ms N = 2^22 7530ms

strictly speaking, it should be 2^15, but this is an entry-level laptop and 108 ms is almost 100, so I increased N.

I do not really understand r, but, according to this discussion

https://news.ycombinator.com/item?id=25660467

M1 has double cache line size, so I doubled r.

I don't really expect this to be accepted I guess - IETF still recommends the lower values, in 2021 - https://tools.ietf.org/id/draft-ietf-kitten-password-storage-01.html - but I guess to open a discussion?

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[karelbilek]

The new M1 chips (fall 2021) seem to be even faster; but the single-core performance is actually very similar. So I think this won't move the numbers that much.