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

Ard Biesheuvel
2026-04-28T16:30:35Z

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.