s2n VS libhydrogen

Then there was Amazon: https://github.com/aws/s2n-tls

I had high hopes for s2n, but looks like it never really caught on outside of AWS.

I started writing s2n the day after Heartbleed and the first lines of code were for the stuffer interface. A stuffer is a buffer for stuff, and it's like Java buffered I/O for C. You can get a flavor from reading the header: https://github.com/aws/s2n-tls/blob/main/stuffer/s2n_stuffer...

The implementation is incredibly simple. Treat all blocks of memory as blob with a known size and then read/write into those blobs with a cursor to track progress and bounds checks on every access. Fence all serialization/deserialization through a safe low level interface. Not only do you get memory safety (which we later proved using formal reasoning) ... but when you're parsing message formats it lends itself to a declarative coding style that makes it very clear what the structure is. You can also do lifecycle things, like erasing sensitive memory with zeroes when you're done with it, making sure things don't show up in core dumps, etc. BoringSSL introduced a Crypto_bytes API that also did some of this plus bounds checking, and retrofit it into OpenSSL.

OpenSSL on the other hand is a horrific mash up of raw pointer arithmetic, ad-hoc parsers interleaved with business logic and control flow. I could never keep it straight, and it always scared me to review.

It seems to support multiple options but requires you pick at least one of them. https://github.com/aws/s2n-tls/blob/main/docs/BUILD.md#build...

I think GnuTLS is probably the second most popular TLS library, after openssl.

I'll also mentions s2n and rustls-ffi for completeness as C libraries, though the former isn't widely used, and the latter is very experimental still. https://github.com/aws/s2n-tls and https://github.com/rustls/rustls-ffi respectively.

I've seen operating on unauthenticated plaintext enough times to list it as my own pet peeve with AES-GCM. But it's a problem for chunked messages too. A few years ago we released a SCRAM mode that makes very minimal changes to AES-GCM so that it mathematically can't operate on unauthenticated plaintext. https://github.com/aws/s2n-tls/tree/main/scram

> The documentation is kind of vague, but apparently you have to re-enable it regularly.[3]

This is correct. And in the end it means more or less that setting the socket option is more of a way of sending an explicit ACK from userspace than a real setting.

It's not great for common use-cases, because making userspace care about ACKs will obviously degrade efficiency (more syscalls).

However it can make sense for some use-cases. E.g. I saw the s2n TLS library using QUICKACK to avoid the TLS handshake being stuck [1]. Maybe also worthwhile to be set in some specific RPC scenarios where the server might not immediately send a response on receiving the request, and where the client could send additional frames (e.g. gRPC client side streaming, or in pipelined HTTP requests if the server would really process those in parallel and not just let them sit in socket buffers).

[1] https://github.com/aws/s2n-tls/blob/46c47a71e637cabc312ce843...

It looks like by default s2n-quic uses this TLS implementation, which is not based on the ring crate (though it is written in C)

https://github.com/aws/s2n-tls

I would be interested in the other SSL implementations:

- https://github.com/awslabs/s2n

- https://boringssl.googlesource.com/boringssl

- https://bearssl.org/

Are these subpar implementations or there are other reasons not to use these?

To quickly build something with signatures, key exchange and encryption, I'd recommend starting with libhydrogen: https://github.com/jedisct1/libhydrogen

The single round-trip initial Diffie-Hellman key exchange is susceptible to MITM attack, as has been demonstrated to me by a fan of the project. I'll be changing it to XX key exchange from libhydrogen. Either directly, or I'll use libsodium primitives to reimplement the same thing.

See if you can use this library instead of libsodium, as it'll probably work on your raspi zero: https://github.com/jedisct1/libhydrogen (Node bindings: https://github.com/trampi/node-libhydrogen-binding)

Are you possibly thinking of libhydrogen?

https://github.com/jedisct1/libhydrogen

NIST's lightweight cryptography contest is still in progress. When it finishes I'd definitely change to whatever wins. In the iterim you might want to look into the candidates. I happen to like gimli, see libhydrogen for a good library that uses it.