[U-Boot] [PATCH v2] Implement generalised RSA public exponents for verified boot

[Simon Glass]

Hi Michael,

On 30 May 2014 15:03, Michael van der Westhuizen
<michael at smart-africa.com> wrote:
> Hi Simon,
>
> On 30 May 2014, at 10:50 PM, Simon Glass <sjg at chromium.org> wrote:
>
> Hi Michael,
>
> On 30 May 2014 14:47, Michael van der Westhuizen
> <michael at smart-africa.com> wrote:
>
> Hi Simon,
>
> Thanks for the feedback.
>
> I'll take care of the nits and look into removing some special casing.
>
> On 30 May 2014, at 9:04 PM, Simon Glass <sjg at chromium.org> wrote:
>
> Hi Michael,
>
> <snip>
>
>
> /**
> + * num_pub_exponent_bits() - Number of bits in the public exponent
> + *
> + * @key:       RSA key
> + * @k:         Storage for the number of public exponent bits
> + */
> +static int num_public_exponent_bits(const struct rsa_public_key *key, int
> *k)
>
>
> s/k/keyp/ or something like that.
>
> Also is this function able to just use ffs() or similar?
>
>
> flsll() yes, but that's not portable to Linux.
>
>
> Does that matter?
>
>
> This code compiles on the host, so unfortunately yes.  That's the same
> reason I had to work around the lack of handy *_u64 fdt helpers when reading
> the public exponent.

OK, although Linux might have replacements. But if not, perhaps add a
comment as to why you need the helper function.

[snip]

> For example, if you did:
>
>      montgomery_mul(key, result, val, key->rr); /* acc = a * RR / R mod n */
>
>
> Yes, it's sizeof(uint32_t) - that would probably be a good thing to spell
> out too.
>
> result points to tmp, which is going to be repeatedly overwritten in the
> loop, but we need a_scaled to stay constant (as the result of the first
> montgomery_mul) throughout... or did I misunderstand your point?
>
>
> OK I see thanks. Perhaps add a new temporary instead of using memcpy()?
>
>
> And set it up using montgomery_mul?  Would that not be more expensive than a
> memcpy?

On the host? Not sure we care about that. I was really just wondering
if an assignment is better than a memcpy() which makes assumptions
about the format.

Regards,
Simon