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From:   Sandy Harris <sandyinchina@gmail.com>
Date:   Fri, 28 Jan 2022 08:12:20 +0800
Message-ID: <CACXcFmkTiiS3M5B6RtyG=oD9+CqncFR6kQX1SZHvVNshVe=vKQ@mail.gmail.com>
Subject: Re: RFC random(4) We don't need no steenking ...
To:     Eric Biggers <ebiggers@kernel.org>
Cc:     Linux Crypto Mailing List <linux-crypto@vger.kernel.org>,
        "Ted Ts'o" <tytso@mit.edu>, "Jason A. Donenfeld" <Jason@zx2c4.com>,
        Herbert Xu <herbert@gondor.apana.org.au>,
        John Denker <jsd@av8n.com>
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Eric Biggers <ebiggers@kernel.org> wrote:

> On Thu, Jan 27, 2022 at 05:04:07PM +0800, Sandy Harris wrote:
> > Current code in extract_buf() declares a local struct blake2s_state,
> > calls blake2s_init() which uses initialisation constants
>
> Which is good, because BLAKE2s is defined to use certain constants.  If
> different constants were used, then it wouldn't be BLAKE2s anymore, but rather
> some homebrew crypto with unknown security properties (like the old "SHA-1" that
> wasn't really SHA-1).

That's a reasonable argument & something very similar applies to
chacha usage. I do not think it holds water, though, since we
would still use the blake & chacha transforms. Even in blake,
every iteration except the first applies the transform to
arbitrary somewhat random data.

> > and moves data into the chacha state with memcpy().
>
> It's actually XOR'd in.  Please take a closer look at crng_reseed().

You are correct.