no_std

[ShadowJonathan]

In rustls/rustls#40 (comment), @lachlansneff expressed interest in an embeddable DTLS implementation, which I believe (together with #1) could work with smoltcp and friends.

However, rustls does not support no_std, while I think that both crates would need alloc nonetheless, no_std seems to not be a priority or possibility as of yet (see rustls/rustls#157, cc @gurry)

An alternative would be to be able to switch to different cryptographic backends, however, rustls is chosen as one because it can expose much of its innards, and I don't even know if using openssl's ciphersuites directly is possible.

[ShadowJonathan]

I think for this there should actually be a dedicated mode, maybe something that also reduces the amount of ciphers we support, and/or use ring directly, as it has some semblance of no_std support (see briansmith/ring#744)

[ShadowJonathan]

For CCM I probably would want to poke at briansmith/ring#25