The microblog: 2022.08.22 11:28:03

2022.08.22 11:28:03 (1561646369814634497) from Daniel J. Bernstein:

The documentation actually suggests, but doesn't quite say, that, already on Skylake, vector multiplications (used in many crypto implementations) _aren't_ constant-time. Since then I've been doing various scans to try to find inputs triggering variations; nothing to report yet.


2022.08.21 17:27:04 (1561374334714671104) from "Adam Langley (@agl__)":

It appears that Intel doesn't guarantee constant-time execution of _any_ instructions on Ice Lake or later unless a configuration bit is set:

2022.08.21 17:27:05 (1561374336014901249) from "Adam Langley (@agl__)", replying to "Adam Langley (@agl__)" (1561374334714671104):

Ice Lake was released in 2019 but this information is only a few months old. So hopefully multiplication etc actually is always constant-time on existing chips and this is just preparing for the future?