Well, I'm using the Arduino 2560 Mega, so I have 256 KB for code (minus 8 for bootloader), 8KB SRAM and 4 KB EEPROM. So even using the minimum standardized key length of 2048 bits, takes up quite a bit a space. Then the data that it must operate on needs to be handled in very small chunks. Given my time frame, I can't really try to develop (if I even could) this for Arduino so an RSA or ECC library would really be helpful