First thing that I have to decide is to find uC, that suits my needs. My requirements:

• Cheap
• Have some sort of hardware communication (bitbanging would consume scarce CPU time)
• Have sufficient internal memory. To be more specific:
  • Initial hash value: 8 x 32b - CONST
  • constants: 64 x 32b - CONST
  • 10 temporary registers : 10 x 32b - VAR
  • 8 result storing registers: 8 x 32b - VAR
  • also input memory, at least 8 x 32b - VAR
  • tens/hundred of bytes for iteration, initialization of UART, etc

  Once added, numbers are as follows:

  • VARIABLE: 104 Bytes + program
  • CONSTANTS: 288 Bytes + program
• platform, that I know: AVR8, STM32

Long story short, I have to choose between easier (STM32) but boring environment and more challenging (AVR8), but harder. You probably know by now what I choose.

For now I stick to ATXmega128a3u which I have (I've made long time ago). Once Everything will be nice and neat I will port it to the smallest ATTiny possible.