[U-Boot] [PATCH 2/4] rsa: Verify RSA padding programatically

[Simon Glass]

Hi Andrew,

On 11 November 2016 at 14:22, Andrew Duda <andrew.duda at meraki.net> wrote:
> Simon,
>
> So I looked into this more after you asked this, and it looks very
> platform dependent. I tested on two builds: sandbox and a version of
> x86-common. The before/after for sandbox image was
> 5486016-5486800(+784). The before/after for my x86 build was
> 3306100-3305908(-192). So memory saving is anywhere from a few bytes
> to actually more space. But the big motivation is the next two patches
> depend on this change.

OK, well I'm not worried about sandbox, and seeing a saving on a real
x86 board is comforting.

BTW please try not to top-post as it confuses the history.

Regards,
Simon

>
> Thanks,
> Andrew
>
> On Fri, Nov 11, 2016 at 8:17 AM, Simon Glass <sjg at chromium.org> wrote:
>> On 8 November 2016 at 11:53, aduda <aduda at meraki.com> wrote:
>>> From: Andrew Duda <aduda at meraki.com>
>>>
>>> Padding verification was done against static SHA/RSA pair arrays which
>>> take up a lot of static memory, are mostly 0xff, and cannot be reused
>>> for additional SHA/RSA pairings. The padding can be easily computed
>>> according to PKCS#1v2.1 as:
>>>
>>>   EM = 0x00 || 0x01 || PS || 0x00 || T
>>>
>>> where PS is (emLen - tLen - 3) octets of 0xff and T is DER encoding
>>> of the hash.
>>>
>>> Store DER prefix in checksum_algo and create rsa_verify_padding
>>> function to handle verification of a message for any SHA/RSA pairing.
>>>
>>> Signed-off-by: Andrew Duda <aduda at meraki.com>
>>> Signed-off-by: aduda <aduda at meraki.com>
>>> ---
>>>
>>>  common/image-sig.c            |   9 ++--
>>>  include/image.h               |   3 +-
>>>  include/u-boot/rsa-checksum.h |   4 --
>>>  include/u-boot/sha1.h         |   3 ++
>>>  include/u-boot/sha256.h       |   3 ++
>>>  lib/rsa/rsa-checksum.c        | 121 ------------------------------------------
>>>  lib/rsa/rsa-verify.c          |  38 ++++++++++++-
>>>  lib/sha1.c                    |   5 ++
>>>  lib/sha256.c                  |   6 +++
>>>  9 files changed, 61 insertions(+), 131 deletions(-)
>>
>> Reviewed-by: Simon Glass <sjg at chromium.org>
>>
>> How much memory does this save?