For a new MANET protocol I started to verify the security concept. Not from a security point of view, rather from a protocol feasibility point of view. The security concept is based on existing security protocols. I just removed dynamic components like key exchange and the like (to be correct: dynamic aspects are done by special messages and not that tight linked with the protocol). The result should be a very lean TLV, containing only required security data without padding issues are "reserved" bits. The default encryption algorithm is still AES128 and authentication (HMAC) is done via SHA-512 (if used separately). So nothing special here. By the way: it is a UDP based MANET protocol, IPSec and OpenSSL are not suitable - DTLS is also not suitable.
At the time I started to implement the security relevant bits I was a little bit annoyed about OpenSSL. OpenSSL has a usable API and the provided functionality is large. But that is the problem: OpenSSL is just a big monster of code and functionality. If you have a stripped demand of functionality like en(de)cryption and checksumming you even have to link the whole OpenSSL library into your program (library).
Some days ago I stumbled across NaCl (pronounced "salt") a lightweight encryption/decryption/checksumming library. Focus: speed and security. I like the API and started to use NaCL for the project. Another nice argument: there are packages for Debian and Ubuntu available in the official repository!
#include "crypto_secretbox.h" const unsigned char k[crypto_secretbox_KEYBYTES]; const unsigned char n[crypto_secretbox_NONCEBYTES]; const unsigned char m[...]; unsigned long long mlen; unsigned char c[...]; unsigned long long clen; crypto_secretbox(c, m, mlen, n, k);