Encrypt communication between Arduino and PC (RC4, XXTEA)

Projects Interfacing w/ Software on the Computer
1

Hi, I would like to secure communication between Arduino and PC. Arduino is connected with PC via Ethernet, in second project via RS-232. I need something independent on type of connection.

I tried AES, but it to hard for ATmega328. It works, but my program is now too complicated and Atmega do not have enough performance.

I do not need security like Internet banking. I need security against home users with WireShark...

I read something about RC4 and XXTEA. What is difference between this?
I found that XTEA is blockcipher and RC4 is streamcipher.

For example: I read data from about 5 thermometers. So I have five ints like 2135 (temp/10). I need securely transfer these ints to pc.
I preffer to use static password in Arduino and PC for pair arduino-pc.

I found these implemetation of RC4, it looks simple.

What is better for my? XTEA, RC4, or somehing different?

2

This XTEA is very simple and short : Arduino/libraries/Xtea at master · franksmicro/Arduino · GitHub
It encrypts 8 bytes.

This XXTEA has a lot more code : GitHub - alessandro1105/XXTEA_Arduino_Library

This RC4 is very small : GitHub - shirokuade/RC4-Arduino: An encryption method code implement in arduino.

Five integers is 10 byte. Plus a timestamp of 4 bytes maybe ? and 2 bytes for a random number. That would be 16 bytes.

When you use an encryption, add a randon number to your data. The better the random is, the better the encryption.
You could for example read noise from an analog input. Or use timing when a button is pressed.

For information about XTEA, XXTEA, RC4, check wikipedia.