Re: [PATCH v2] crypto: atmel-sha204a - drop hwrng quality reduction for ATSHA204A

Ard Biesheuvel
2026-04-28T10:18:30Z

On Tue, 28 Apr 2026, at 12:14, Thorsten Blum wrote:
> Commit 8006aff15516 ("crypto: atmel-sha204a - Set hwrng quality to
> lowest possible") reduced the hwrng quality to 1 based on a review by
> Bill Cox [1]. However, despite its title, the review only tested the
> ATSHA204, not the ATSHA204A.
>
> In the same thread, Atmel engineer Landon Cox wrote "this behavior has
> been eliminated entirely"[2] in the ATSHA204A and "this problem does not
> affect the ATECC108 or the ATECC108A (or the ATSHA204A)"[3].
>
> According to the official ATSHA204A datasheet [4], the device contains a
> high-quality hardware RNG that combines its output with an internal seed
> value stored in EEPROM or SRAM to generate random numbers. The device
> also implements all security functions using SHA-256, and the driver
> uses the chip's Random command in seed-update mode.
>
> Keep 'quality = 1' for ATSHA204, but drop the explicit hwrng quality
> reduction for ATSHA204A and fall back to the hwrng core default.
>
> [1]
> https://www.metzdowd.com/pipermail/cryptography/2014-December/023858.html
> [2]
> https://www.metzdowd.com/pipermail/cryptography/2014-December/023852.html
> [3]
> https://www.metzdowd.com/pipermail/cryptography/2014-December/023886.html
> [4]
> https://ww1.microchip.com/downloads/en/DeviceDoc/ATSHA204A-Data-Sheet-40002025A.pdf
>
> Fixes: 8006aff15516 ("crypto: atmel-sha204a - Set hwrng quality to
> lowest possible")
> Cc: stable@vger.kernel.org
> Signed-off-by: Thorsten Blum <thorsten.blum@linux.dev>

Reviewed-by: Ard Biesheuvel <ardb@kernel.org>