Serializing data created by ATTiny85 for use on PC 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?
So thanks to Ignacio Vazquez-Abrams' tip, it looks like I'll be able to accomplish this with V-USB:


  V-USB is a software-only implementation of a low-speed USB device for
  Atmel’s AVR® microcontrollers, making it possible to build USB
  hardware with almost any AVR® microcontroller, not requiring any
  additional chip.


Requirements: AVR microcontroller with at least 2 kB of Flash memory, 128 bytes RAM and a clock rate of at least 12 MHz.

Taken from ATTiny85's Datasheet:


  
  8K Bytes of In-System Programmable Program Memory Flash
  512 Bytes In-System Programmable EEPROM (enough for third-two 16-byte keys)
  512 Bytes Internal SRAM
  


Looking forward to trying it out :)