Exercise for the reader (out of genuine interest): find the most important cryptographic paper published in the last 15 years that uses the British spelling.

Why the 15 year cut-off?

Besides, I don't doubt the US spelling has taken over, that has happened a lot in a wide range of fields, but it doesn't invalidate the British spelling, even if it isn't as widely used in recent published papers.

It's like claiming that the element is sulfur not sulphur, because papers are increasingly written for an international audience. In British English, the element is Sulphur, regardless of whether you can find an "important paper" using the spelling.

I don't know what the idiom is in chem, but if I was a chemist and you used idiosyncratic layperson spelling, I would get signal from that.

Isn't it true that OED say that "cipher" is the primary, preferred spelling in modern British English?