Have an AES-128 implementation I'd like to install on an ATTiny85 for embedded use but need to come up with a way to communicate with it from a PC as you would do via Serial on Arduino Uno. For example, I'd like to stream 16 bytes of plaintext and get back 16 bytes of ciphertext (or signature hash, etc.).
The faster the transfer rate, the better obviously, but it would of course need to fit on the remaining space on an ATTiny85.
Any thoughts or working examples out there (i.e. I2C for PC, etc.) without incurring a lot of extra hardware cost?