How to generate random numbers?

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Furs

Joined: 04 Mar 2016
Posts: 2565

Furs 01 Jun 2022, 13:01

revolution wrote:

Random generators of bits don't appear in the source code. They are random, that's the point. Each time you run to code it works with different values from the generator.

If the RNG is some hardware component, or some external component (like network timing, keystroke timing, mouse movements, clock drift, etc.), then it is fine for the software source code to be open, the data don't come from the source code. The software only works with the data it is given. Unpredictable data in => secure outputs.

It's all a solved problem. Cryptographers actually only consider something secure if they can see all the inner workings and still can't predict the outputs. Or they treat it with suspicion if it is a secret and can't examine it.

Intel, what are you hiding? Show your implementation and prove it is genuine.

Why does it matter? I seriously don't understand your skepticism.

Someone said to use rdtsc as a seed source. rdtsc is clearly defined how it works and you can even predict it (based on when the app was ran). Even if the NSA could predict rdrand the same way it can't be worse than rdtsc, since they can clearly do it for rdtsc as well.

So rdrand is at least as good as any other "known" source. Security by obfuscation is not worse than "open" sources that you already know anyway, in fact it takes extra step to find out how it works, even if you're the NSA. Sure such steps might be trivial, but it can't be worse.

Next you're gonna say "well if you use rdrand just for source it should be fine", but then you also said that "mixing bits" is pointless if the source is bad, so...? Isn't that what you're doing with a prng and rdtsc seed...?

01 Jun 2022, 13:01

revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 20451
Location: In your JS exploiting you and your system

revolution 01 Jun 2022, 13:11

rdtsc is not random, it can be predicted.

rdrand might be fully random, or only be somewhat random, or maybe not random at all, Intel won't show us.

Keystrokes timing, clock drift/skew/jitter, other known good sources of real random data can't be predicted. So use those if you need actual random data.

Cryptographers demand all code and hardware to be open sourced, so it can be examined and analysed. It is part of the process to be considered good for use. It isn't security by obfuscation, it is the opposite, it is security by clearly demonstrated "nothing to hide", just good pure randomness emanating from the system.

rdrand is security by declaration. Intel says "trust us". Lol, nope, sorry it doesn't work that way.

Last edited by revolution on 01 Jun 2022, 14:23; edited 1 time in total

01 Jun 2022, 13:11

revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 20451
Location: In your JS exploiting you and your system

revolution 01 Jun 2022, 13:16

Furs wrote:

Next you're gonna say "well if you use rdrand just for source it should be fine", but then you also said that "mixing bits" is pointless if the source is bad, so...? Isn't that what you're doing with a prng and rdtsc seed...?

What I actually said was for " non-cryptographic purposes it will be fine"

Something trivial like choosing a "random" tip of the day, or similar, it's fine, do whatever.

Totally different if you want to create secure keys for your Bitlocker disks. Don't use insecure sources, or unverified sources, for those.

01 Jun 2022, 13:16

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