Found a package called randomsound that uses audio cards as entropy source. Maybe I should re-add sound to the gateway in that case? Question is if it works with speakers muted and also if we need to be playing something for it to generate entropy.
I need to contact the upstream dev to know more
IRC: Kinnison, OFTC, #debian-uk
One of vanheusden’s daemons are already packaged for Fedora. Perhaps we can attempt converting them to .deb with Alien.
Both video-entropyd and audio-entropyd need access to sound and visual output so perhaps they would make sense more outside the VM while TimerEntropyd goes inside.
audio-entropyd (make sure your microphone isn’t muted), and video_entropyd (needs a camera or video input, might be able to hook up an analog antenna to a TV Tuner and set it to a static channel. It might also suck up some CPU cycles, so be careful)
libprngwrap uses LD_PRELOAD magic to force the few dumb programsleft that insist on using /dev/random to be redirected to urandom instead. Not sure if useful anymore when jitterentropy handles /dev/random and stops its blocking.
randomsound developer replied to the mailing list:
(But somehow the reply does not (yet) show up on the mailing list archive.)
From: Daniel Silverstone
On Sat, Nov 23, 2019 at 20:29:48 +0000, firstname.lastname@example.org wrote:
Hi Dan. I’m a privacy distro dev and we are thinking of including
randomsound as an entropy source by default.
I’d recommend against that, reasoning below…
Does it gather entropy at all times when a soundcard is connected or only when there is sound playing?
It was designed to gather sound at all times it was running.
I assume form the package description it relies on sound output and not microphone input unlike van Heusden’s audio-entropyd
It was meant to use an input line, microphone or line-in.
How well can it function in a virtual environment?
Probably not usefully at all.
Randomsound was written a long time ago when computer hardware was simpler and less careful in terms of sound design. It was common for sound cards to be fairly (a) electrically noisy and (b) configurable. As such, I had a server which had need of entropy and a sound device which had no microphone or line-in device attached, and a sound card which could decouple its level monitoring from any controls (leave it floating) – this combination gave me a source of electrical and thermal noise I could harvest.
These days sound cards have mandatory filtering and are sufficiently complex that I would not like to make any assertions about an ability to set one up in the manner I recommended for use with randomsound. Virtual devices are even more controlled and thus even less likely to provide access to the kinds of entropy randomsound attempted to harvest.
These days I’d recommend ensuring that host systems harvest entropy from as many sources as possible, optionally sharing them around among themselves (I believe there’s software for this kind of thing) and then qemu has a virtio-rng device which allows transfer of entropy from host to guest (at a controlled rate).
There are also devices one can purchase which can increase the available entropy pool if your hosts are regularly running dry. For example the chaoskey by Keith Packard and Bdale Garbee.
Good luck with your quest for entropy, and thank you all for taking privacy so seriously.
No reports of anything is blocking now (before jitterentropy kernel module gets load) or later. Without any reports of anything blocking, I don’t think blocking would be an issue even if blocking somewhere. Blocking as far as I understand just means slower. Not catastrophic.
In sort libprngwrap enhances the PRNGs from libc. libprngwrap replaces the [s]rand, [s]random and [*]rand48 library calls with functions that get random values from /dev/urandom. This is supposed to be more secure.
Does not sound like a /dev/random vs /dev/urandom thing.
When your Linux system uses a lot of entropy-data from the /dev/random or /dev/urandom device, it might get empty and stall your application (in case of /dev/random) or return less secure data (in case of /dev/urandom).
There we have it again, “less secure data (in case of /dev/urandom”.
VideoEntropyd is like timer-entropyd for a ‘video-4-linux’-compatible device. E.g. a tv-card or a webcam.
In our security guide we recommend to disable webcams in BIOS, to cover them or even physically remove them. Therefore worth bothering with it? If a webcam was blocked with a sticker would there be any noise that would generate randomness? The author will probably say we should check for ourselves. Any contributors coming to mind up to test that? Worth it? (Would be done on the host. Not inside VM. Any entropy enhancement of the host also makes VMs benefit.)
EGD - The Entropy Gathering Daemon looks quite old already. Worth contacting its author asking if it could still be useful nowadays? Useful to redirect its output of entropy to /dev/random?
I’ll ask but audio_entropyd seems to be a different implementation which doesn’t blindly copy data until it meets sufficient entropy measures
The audio-data is not copied as is but first ‘de-biased’ and analysed to determine how much bits of entropy is in it.
Not clearly known. I’ll need to ask the author to confirm. The wiki description seems to describe differing implementations of a similar concept. I guess each unique algorithm will have its own take of the same source and add more noise?
Then let’s change the recommendation. A lot of damage can be done if attacker roots the host. They can spy using the speakers and even HDD platters and so removing access to devices in the TCB is of marginal benefit.
I don’t mind testing , but we must have some entropy measure to gauge the effectiveness.
I am skeptical about the approach of fetching entropy from remote sources.
What’s the intended benefit of the users and what use do others interpret into it? The intended benefit the by author might be “make my cloud image work” and then the security interested users might think “it’s to improve the security/entropy of my system”. Therefore we’d have to research that and perhaps ask the author if intended/tested use cases and limitations aren’t spelled out yet.
To use https securely (to connect to an entropy source) you need entropy to begin with (SSL session key). Well, I guess against adversaries who don’t try to MITM this might even improve entropy.
Is it worth the added attack surface, risk of exploitation by a compromised entropy source server?
Kernel is supposed to never worsen entropy no matter if a third party predicable source is added to and mixed with other legit entropy sources. However, how much do we want to trust this, add a potentially compromised third party remote source into the mix?
Me too. It’s just a mere curiosity. His package description made me wonder if it is possible to use a unsafe source of randomness and make it safe. I don’t think the added remote attack surface is worth it either, but something to learn about how entropy works.
If that is the case then theoretically the code could be implemented to support untrusted local hwrngs and mitigate all risks while adding value.
I have written a daemon program which I believe solves this problem. I wanted a name distinct from the existing“Timer entropy daemon” , developed by Folkert vanHeusden, so I named minemaxwell(8), after Maxwell’s demon, an imaginary creature discussed by the great physicist James Clerk Maxwell. Unlike its namesake, however, my program does not create exceptions to the laws of thermodynamics.
The timer entropy daemon uses floating point math in some of its calculations. It collects data in a substantial buffer, 2500 bytes, goes through a calculation to estimate the entropy, then pushes the whole load of buffered data into random(4). My program does none of those things.
Uses a related method (jitter in timing data between usleeps) as this module, but inefficient and only suitable for bulk feeding of an entropy pool. Even after von Neumann debiasing, the output has distinct patterns and at most 0.5 bits of entropy per output bit. HAVEGE is a superior overall solution. However, note a number of other links at the site for other sources as well as links to hardware RNGs.
The timer entropy daemon uses timing jitters over sleeps to produce entropy, much like MAXWELL. This demon is even more lightweight than MAXWELL, and makes no attempt to spice things up by doing small calculations, rather it only uses a 100 s sleep wrapped by gettimeofday(2) sampling.