From: "Ard Biesheuvel" <ardb@kernel.org>
To: "Marek Behún" <kabel@kernel.org>,
"Thorsten Blum" <thorsten.blum@linux.dev>
Cc: "Bill Cox" <waywardgeek@gmail.com>,
"Herbert Xu" <herbert@gondor.apana.org.au>,
"David S. Miller" <davem@davemloft.net>,
"Nicolas Ferre" <nicolas.ferre@microchip.com>,
"Alexandre Belloni" <alexandre.belloni@bootlin.com>,
"Claudiu Beznea" <claudiu.beznea@tuxon.dev>,
"Linus Walleij" <linusw@kernel.org>,
stable@vger.kernel.org, linux-crypto@vger.kernel.org,
linux-arm-kernel@lists.infradead.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2] crypto: atmel-sha204a - drop hwrng quality reduction for ATSHA204A
Date: Tue, 28 Apr 2026 18:30:05 +0200 [thread overview]
Message-ID: <e4091e56-0230-48fb-bd31-e617c32b6348@app.fastmail.com> (raw)
In-Reply-To: <cbk4ho3bpprjxvcywv4sudbmb2fhfsgaguoywv5mhtoql4vhd6@f7oisxcrvii4>
On Tue, 28 Apr 2026, at 15:24, Marek Behún wrote:
> Hi Thorsten,
>
> Bill also wrote about ATSHA204A [1]
>
> My best guess as to what's going on here is that the device has a
> ring-oscillator based entropy source, but that it generates only a few bits
> of entropy for each use. It seems to be called before generating each
> 32-byte "random" value, which is why the second set of 32-bit values have
> more possible values, and the 3rd has even more. However, the number of
> unique values in the final column of 32*N byte values is always equal to
> the number of unique values of the entire string of bytes.
>
> If this is true that the device generates <256 true random bits and then
> mixes in non-volatile pseudorandom number generator to produce 256 bits,
> then the quality should not be set to full 1024.
>
This post is about the Hashlet, which has a ATSHA204 not ATSHA204A.
prev parent reply other threads:[~2026-04-28 16:30 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-04-28 10:14 [PATCH v2] crypto: atmel-sha204a - drop hwrng quality reduction for ATSHA204A Thorsten Blum
2026-04-28 10:18 ` Ard Biesheuvel
2026-04-28 11:18 ` Marek Behún
2026-04-28 12:18 ` Ard Biesheuvel
2026-04-28 12:32 ` Thorsten Blum
2026-04-28 13:24 ` Marek Behún
2026-04-28 16:30 ` Ard Biesheuvel [this message]
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