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 b

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.h 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.