Simple (but good) Message Encryption?

I want to have a simple and good encryption and decryption as a balance of size and security.

On ESP8266 there will be no https with Espruino as far as I unterstand. So I was thinking about to secure the content thats being send and received. TEA seems to be simple to implement in C or in JS, both are available as source in this thread.

Tried to include AES on ESP8266, looks like no one tried this before :)

.....
libs/crypto/jswrap_crypto.c: In function 'jswrap_crypto_AES_encrypt':
libs/crypto/jswrap_crypto.c:433:3: error: implicit declaration of function 'jswrap_crypto_AEScrypt' [-Werror=implicit-function-declaration]
   return jswrap_crypto_AEScrypt(message, key, options, true);
   ^
libs/crypto/jswrap_crypto.c:433:3: warning: return makes pointer from integer without a cast [enabled by default]
libs/crypto/jswrap_crypto.c: In function 'jswrap_crypto_AES_decrypt':
libs/crypto/jswrap_crypto.c:452:3: warning: return makes pointer from integer without a cast [enabled by default]
   return jswrap_crypto_AEScrypt(message, key, options, false);
   ^
libs/crypto/jswrap_crypto.c: At top level:
cc1: warning: unrecognized command line option "-Wno-float-conversion" [enabled by default]
cc1: warning: unrecognized command line option "-Wno-discarded-qualifiers" [enabled by default]
cc1: some warnings being treated as errors
make: *** [libs/crypto/jswrap_crypto.o] Error 1
make: *** Waiting for unfinished jobs....