all. I'm checking dtls library. I've found some libraries for dtls implementation. Especially, tinydtls library is for class 1 device which has limitation like constrained resource and data size. and, some functionalities are disabled from general dtls. But, I have no idea which functionalities is limited for tinydtls. Can you please let me know which functionalities is limited from general dtls and what exactly difference between dtls and tinydtls?
tinydtls doesn't support X.509 certificate (probably not a big deal to add it).
Also it's designed for 6LowPAN, it tends to not aggregate handshake messages in the same UDP packet but in multiple packets. It's supporting only the CoAP oriented ciphersuite (ex: AES CCM-8) Resume is also not supported.
Outside of that, it's really compact and the code is clear.
mbed tls or gnu tls also implement DTLS