How to decrypt the data payload of a XBEE 802.15.4 packet with the key ?

On the devices Xbee S1, how to encrypt and decrypt the data payload of the packet when we know the key ?
Normally, the security level is known thanks to a flag in the packet but with the XBEE S1, the flag is None…
AES-CTR is used ?

You are not suppose to decrypt a packet without knowing what the Key is. That is the purpose of using encryption.

Thank you for your answer.

I do not think I made myself clear enough though. My objective is to decrypt a 802.15.4 packet sniffed and encrypted by a xbee s1 module. Of course, I know the key…
Normally a nonce is used and I don’t know what it is. Also, I 'm not sure what Aes (CTR, CCM…) is used.
Someone know all the parameters to encrypt and decrypt a xbee s1 encrypted packet ?

You are going to need to look throiugh the IEEE 802.15.4 protocol to locate the required AES encryption altroythum to figure that out.

Normally, in the 802.15.4 packet, there is a flag that indicate what AES is used.
Here, with the Xbee S1, the flag is not used. Do you know what AES xbee s1 use ?