Does MQTT-SN provide any encryption like AES-128 etc.? As I know, it's using a simple binary encryption but in my opinion this cannot be seen as a security feature. Many thanks in advance :)
No, MQTT-SN doesn't supply any encryption at a protocol level, but you are free to encrypt the payload yourself how ever you want.
Also since MQTT-SN doesn't make any requirements on what transport is used to carry the packets, but you could build a system that uses DTLS (similar to how CoAPS works)