Re: Fortuna

David Wagner
2005-04-16T01:27:37Z

Theodore Ts'o wrote:
>With a properly set up set of init scripts, /dev/random is initialized
>with seed material for all but the initial boot [...]

I'm not so sure. Someone posted on this mailing list several months
ago examples of code in the kernel that looks like it could run before
those init scripts are run, and that looks like it might well be using
/dev/*random before it has been seeded.

I never saw any response.

>It fundamentally assumes that crypto
>primitives are secure (when the recent break of MD4, MD5, and now SHA1
>should have been a warning that this is a Bad Idea (tm)),

It looks to me like the recent attacks on MD4, MD5, and SHA1 do not
endanger /dev/random. Those attacks affect collision-resistance, but
it looks to me like the security of /dev/random relies on other properties
of the hash function (e.g., pseudorandomness, onewayness) which do not
seem to be threatened by these attacks. But of course this is a complicated
business, and maybe I overlooked something about the way /dev/random uses
those hash functions. Did I miss something?

As for which threat models are realistic, I consider it more likely
that my box will be hacked in a way that affects /dev/random than that
SHA1 will be broken in a way that affects /dev/random.

>In addition, Fortuna is profligate with entropy, [...]

Yup.