In my IOT project, I use the xxTEA encryption algorithm to encrypt my data. I use the same encryption key for all my packets because I don't have the possibility to do a key exchange between Alice and Bob.
I want to know how many packets it would take to deduce my key. I looked on the document of Alex Biryukov named "Differential cryptanalysis to ciphertext-only attacks" (https://link.springer.com/content/pdf/10.1007%2FBFb0055721.pdf) but I don't understand everything and can't find the calculation that gives me the result I'm looking for.
I send two packet per minute and I search to know how often do I have to change my key, before my encryption becomes insecure.
If anyone has any suggestions, I'd love to hear them. Thanks in advance.