3 ms·

> To get time invariance I have to To get time invariance all I need is a clock. Responses are normalized to some value greater than the slowest computation.

> To get time invariance I have to To get time invariance all I need is a clock. Responses are normalized to some value greater than the slowest computation. Thus, I don't need exclusive, explicit and complete control of all layers, including whatever inevitable evolution those layers incur without my knowledge. Barring any further threat model inflation involving ammeters, spectrum analyzers or what have you, how is this not a sufficient solution?

sdenton4 3y ago
What is a 'computation' exactly, and how do you know the duration of the slowest one? I imagine the complexity spirals as you try to answer those two questions...
- topspin 3y ago
  > What is a 'computation' exactly Execution of whatever one proposes to code in a time invariant manner. In this case: "RSA decryption and signing operations." > I imagine the complexity spirals Measuring things and normalizing operation time doesn't appear terribly complex to me. How can endlessly reworking subtle algorithms for new compilers and hardware seem less complex than throttling well understood implementations with a clock? Also, I asked a question. My question was sincere: how would using a clock to normalize operation time not be sufficient?
  - sdenton4 3y ago
    Measuring and normalizing the operations isn't necessarily straightforward - suppose we're in a streaming context (common for encrypting things for the internet), in a real-world environment, where computation time might depend on what other applications are running, or the temperature of the CPU; max operation time will vary over time and possibly unobservable changes in circumstances. It's easy to spitball a seemingly 'good-enough' solution to this, but crypto doesn't seem to be a place where 'good-enough' is actually good enough. https://superuser.com/questions/432579/how-is-cpu-temperature-related-to-clock-frequency-and-processor-utilization https://superuser.com/questions/432579/how-is-cpu-temperatur...

sdenton4 3y ago

What is a 'computation' exactly, and how do you know the duration of the slowest one? I imagine the complexity spirals as you try to answer those two questions...

topspin 3y ago
> What is a 'computation' exactly Execution of whatever one proposes to code in a time invariant manner. In this case: "RSA decryption and signing operations." > I imagine the complexity spirals Measuring things and normalizing operation time doesn't appear terribly complex to me. How can endlessly reworking subtle algorithms for new compilers and hardware seem less complex than throttling well understood implementations with a clock? Also, I asked a question. My question was sincere: how would using a clock to normalize operation time not be sufficient?
- sdenton4 3y ago
  Measuring and normalizing the operations isn't necessarily straightforward - suppose we're in a streaming context (common for encrypting things for the internet), in a real-world environment, where computation time might depend on what other applications are running, or the temperature of the CPU; max operation time will vary over time and possibly unobservable changes in circumstances. It's easy to spitball a seemingly 'good-enough' solution to this, but crypto doesn't seem to be a place where 'good-enough' is actually good enough. https://superuser.com/questions/432579/how-is-cpu-temperature-related-to-clock-frequency-and-processor-utilization https://superuser.com/questions/432579/how-is-cpu-temperatur...