Serializing data created by ATTiny85 for use on PC
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 :)