Does a SIM card consist of only Flash memory or is there a microprocessor inside as well?
Best Answer
There is a small microcontroller inside.
Most SIM cards these days can be programmed in Java and follow the JavaCard / GlobalPlatform standard. You won't get the keys to install your own applications though.
The ETSI standardETSI TS 102 221 describes the procedure for switching (and thus finding the appropriate) supply voltage in section 6.2:
6.2 Supply voltage switching
The terminal shall initially activate the UICC with the lowest voltage
class available. If no ATR is received, the UICC shall be deactivated
and activated with the next higher class, if supported by the
terminal. If an ATR is received at the first applied voltage class,
the contents of the ATR shall be analysed by the terminal. If the
operating class used by the terminal is not supported by the UICC, the
terminal shall deactivate the UICC and activate it with a supply
voltage class indicated by the UICC. If the ATR is corrupted, the
terminal shall perform the procedure at least 3 times using the same
operating class before rejecting the UICC. In case of 3 consecutive
corrupted ATRs, the terminal may activate the UICC with the next
higher class. The terminal is restricted not to use but the next
higher class in the retrial attempt in this case.
The "SIM Reader" and a few wires appears to be all the hardware needed to interface a SIM card to an Arduino.
There seem to be some Python scripts designed to talk to it over a serial port;
perhaps you wouldn't find it too difficult to translate to something (C++) that runs on an Arduino.
Most SIM cards today have "applications" that run on the little CPU in the SIM card stored in the flash of the SIM card.
-- "A brief introduction to the SIM-cards"
more general answer
No matter which chip the crypto software is running on, it seems better to generate and keep the key inside that same chip.
It seems to be easier to write software that implements public-key encryption to run on a AVR than to run on a smart card. If you run the crypto on the AVR chip, then it would be better to keep the secure key inside the AVR chip rather than try to store it externally.
Public-key encryption (combined with symmetric encryption like AES) seems to be more generally useful than any symmetric encryption system alone.
It sounds like you may be interested in the "Pico: No more passwords!" system; see also the early "Pico: No More Passwords!" video.
Best Answer
There is a small microcontroller inside.
Most SIM cards these days can be programmed in Java and follow the JavaCard / GlobalPlatform standard. You won't get the keys to install your own applications though.