8 ms·
I've worked in crypto before (not now though) and your statement is actually a common misconception. The information about whether the randomness is sourced fro
by banachtarski 7y ago
I've worked in crypto before (not now though) and your statement is actually a common misconception. The information about whether the randomness is sourced from "true" entropy or not is in and of itself a form of entropy from the perspective of an assailant. It's enough that given some period of time, "some" amount of entropy is present and how much is dependent on the degree to which the system is used. You can use a game theoretic approach to determine how much that is.
edit: to clarify, occasionally not using /dev/random when it may block is not actually a security issue (in most cases)
- ses1984 7y agoHow do we know which cases?
- deleted 7y ago[deleted]
- masklinn 7y agoThe only case where it could be an issue is at bootup, when the subsystem simply does not have enough entropy. OpenBSD solved that by storing a seed for next bootup at the end of boot and during shutdown.
- simonh 7y agoI hope the seed is very well protected.
- VibrantClarity 7y agowdym? if an attacker can access your filesystem its already game over
- iforgotpassword 7y agoThe same could be said for some of the entropy sources that were nerfed or removed over time due to security concerns. That's the main reason why we even are in this situation today.
- asamarin 7y agoSo what happens at the very first boot (e.g. after system installation, or cloud instance just being spawned)? Is that the only circumstance where it would be OK to block? Does OpenBSD trust RdRand for such occasions?
- ChrisSD 7y agoYou can set /etc/random.seed (or /var/db/host.random for spawned instances) prior to first boot. That's what cloud providers do IIRC. It also mixes in hardware random (if available).
- gnud 7y agoA new cloud instance seems like a small problem. The host could just generate an entropy file for the first boot.
- caf 7y agoYes - the hard case is a little flash-based low power ARM router, cloned by the million.
- Reelin 7y agoFrom 2012, but still at least somewhat relevant (https://factorable.net/weakkeys12.extended.pdf https://factorable.net/weakkeys12.extended.pdf). > RSA and DSA can fail catastrophically when used with malfunctioning random number generators ... network survey of TLS and SSH servers and present evidence that vulnerable keys are surprisingly widespread ... we are able to obtain RSA private keys for 0.50% of TLS hosts and 0.03% of SSH hosts, because their public keys shared nontrivial common factors due to entropy problems, and DSA private keys for 1.03% of SSH hosts, because of insufficient signature randomness ... the vast majority appear to be headless or embedded devices ...
- boring_twenties 7y ago> Does OpenBSD trust RdRand for such occasions? It is used as one source among many to seed the PRNG, so I think the answer is no.