[PATCH v2 1-2/2] use ecdh/X25519 from openssl when possible (openssl-1.1.1+)

[Ben Lindstrom]

Suspect you'd get more traction by targeting libressl.  As that is what 
upstream uses.

Ben

Yuriy M. Kaminskiy wrote on 2/18/19 2:29 PM:
> On 17.02.2019 15:46, Yuriy M. Kaminskiy wrote:
>> See attached:
>>
>> (1) patch against 7.9p1, tested with openssl 1.1.0j and openssl
>> 1.1.1a on linux/i386; passes regression test and connects to
>> unpatched sshd without problems;
> As ed25519-from-openssl patch came out a bit less convoluted, I've
> tried to do same with ecdh/x25519.
>
> So, here are V2:
> (1) use openssl-1.1.1a api,
> (2) [optional] emulate openssl-1.1.1a api for openssl-1.1.0.
>
> Unfortunately, it was a bit slower (as it needs to (de)serialize
> private key):
>
>> I hacked a bit regress/unittests/kex, and benchmarked
>>      do_kex_with_key("curve25519-sha256 at libssh.org", KEY_ED25519, 256);
>> Before:
>>    0.3295s per call
>> After:>   0.2183s per call
> openssl/1.1.0j, curve25519 + ecdsa-sha256 (openssh's builtin eddsa is too slow,
> so difference between V1 and V2 is lost in noise, so I replaced ed25519
> with ecdsa/p256 for this test)
>
> ecdh/25519 V1:
>     0.0185s per call
> ecdh/25519 V2:
>     0.0205s per call
>
> openssl/1.1.1a, curve25519 + ed25519 (with ed25519 patch)
> ecdh/25519 V1:
>      0.0115s per call
> ecdh/25519 V2:
>      0.0131s per call (worse by 14%)
>
>> That is, 50% speedup; assuming ed25519 (added to openssl in 1.1.1)
>> takes about same time as ecdh/x25519, there are potential for total
>> 200% speedup in KEX.
>>
>> (2) rebased patch against git master; passes regression test;
>>
>> I relied on presence of NID_X25519 for autodetection; probably it
>> makes sense to check if is actually working it autoconf; then again,
>> maybe not (it won't work when cross-compiling anyway).
>>
>> P.S. given amount of feedback I received so far, it seems everyone
>> follows motto "it cannot be secure if it is not slow".
>
>
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