[axtls-general] axTLS with support for PSK ciphersuites

[Mordy O. <mor...@gm...>]

All,
I made a version of axTLS with support for TLS's preshared keys
ciphersuites:
https://github.com/mordyovits/axtls-svn-mirror/tree/add-psk-ciphers

In many IoT use cases PSK ciphersuites are useful (though they're not
useful for connecting to typical HTTPS services).  There are a few big
advantages to PSK in IoT:

1) Performance. There's no RSA operations ever, so it's fast and uses
little energy in handshaking.

2) Size. Configuring axTLS with PSK support strips out support for the RSA
ciphersuites.  I did it this mutually-exclusive way (with Cameron Rich's
blessing) because few uses cases need both kinds of ciphersuites.  More
importantly, it means that a PSK build of axTLS is truly tiny, since all
the RSA, bigint, X.509, and ASN.1 code is #ifdef-ed away.

I emailed Cameron about my work and he was interested in it.  I don't know
where he stands on merging it, but I appreciate any opinion on it.

Thanks,
Mordy