Re: [PATCH net-next v3 02/17] zinc: introduce minimal cryptography library

On 13 September 2018 at 17:58, Jason A. Donenfeld [off-list ref] wrote:

On Thu, Sep 13, 2018 at 5:43 PM Ard Biesheuvel
[off-list ref] wrote:

quoted

I'd prefer it if all the accelerated software implementations live in
the same place. But I do strongly prefer arch code to live in
arch/$arch

Zinc follows the scheme of the raid6 code, as well as of most other
crypto libraries: code is grouped by cipher, making it easy for people
to work with and understand differing implementations. It also allows
us to trivially link these together at compile time rather than at
link time, which makes cipher selection much more efficient. It's
really much more maintainable this way.

quoted

I think AES-GCM is a useful example here. I really like the SIMD token
abstraction a lot, but I would like to understand how this would work
in Zinc if you have
a) a generic implementation
b) perhaps an arch specific scalar implementation
c) a pure NEON implementation
d) an implementation using AES instructions but not the PMULL instructions
e) an implementation that uses AES and PMULL instructions.

The same way that Zinc currently chooses between the five different
implementations for, say, x86_64 ChaCha20:

- Generic C scalar
- SSSE3
- AVX2
- AVX512F
- AVX512VL

We make a decision based on CPU capabilities, SIMD context, and input
length, and then choose the right function.

OK, so given random.c's future dependency on Zinc (for ChaCha20), and
the fact that Zinc is one monolithic piece of code, all versions of
all algorithms will always be statically linked into the kernel
proper. I'm not sure that is acceptable.

quoted

You know what? If you're up for it, let's not wait until Plumbers, but
instead, let's collaborate off list to get this into shape.

Sure, sounds good.

BTW you haven't answered my question yet about what happens when the
WireGuard protocol version changes: will we need a flag day and switch
all deployments over at the same time?