Re: [FFmpeg-devel] [PATCH 1/2] avformat/hlsenc: fall back to av_get_random_seed() when generating AES128 key

From: Michael Niedermayer <michael@niedermayer.cc>
To: FFmpeg development discussions and patches <ffmpeg-devel@ffmpeg.org>
Subject: Re: [FFmpeg-devel] [PATCH 1/2] avformat/hlsenc: fall back to av_get_random_seed() when generating AES128 key
Date: Tue, 4 Jul 2023 01:50:57 +0200
Message-ID: <20230703235057.GQ1093384@pb2> (raw)
In-Reply-To: <168841859463.9711.12513000520212201640@lain.khirnov.net>

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On Mon, Jul 03, 2023 at 11:09:54PM +0200, Anton Khirnov wrote:
> Quoting Marton Balint (2023-07-03 22:54:41)
> > On Mon, 3 Jul 2023, Anton Khirnov wrote:
> > My patch use av_get_random_seed() which uses what the underlying OS 
> > provides, BCrypt for Windows, /dev/urandom for Linux, arc4random() for 
> > BSD/Mac.
> 
> IOW it's a jungle of various paths, some of which are not guaranteed to
> be cryptographically secure. I see no such guarantees for arc4random()
> from a brief web search, and the fallback get_generic_seed() certainly
> is not either. Granted it's only used on obscure architectures, but
> still.
> 
> The doxy even says
> > This function tries to provide a good seed at a best effort bases.
> 
> > You really think that these are significantly worse than
> > OpenSSL/GCrypt, so it should not be allowed to fallback to?
> 
> I think we should be using cryptographically secure PRNG for generating
> encryption keys, or fail when they are not available. If you want to get
> rid of the openssl dependency, IMO the best solution is a new
>   int av_random(uint8_t* buf, size_t len);
> that guarantees either cryptographically secure randomness or an error.

"guarantees cryptographically secure randomness" ?
If one defined "cryptographically secure" as "not broken publically as of today"

Iam saying that as i think "guarantees" can be misleading in what it means

thx

[...]
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Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

The day soldiers stop bringing you their problems is the day you have stopped 
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