Testing target

This repository contains an AVR implementation of an unprotected 128-bit key AES as well as a dummy PIN verification algorithm for playing with the LEIA boards.

The implementations have been tested on a WB Electronics 64 Kbit ATMega chipcard.

Compilation

Go to the src/ folder and run make. You must have avr-gcc, e.g. from avr-gcc, and the avr-libc installed on your PC: these are usually packaged with popular distros such as Debian or Ubuntu. Make should create aes-<DDMMYY>-<HHMMSS>.hex and eedata-<DDMMYY>-<HHMMSS>.hex in the src/build/ folder.

Loading in the ATMega8515 card

Load the files eedata.hex (in EEPROM int.) and aes-<DDMMYY>-<HHMMSS>.hex (in FLASH) in the ATMega8515 component. You can for instance use the Infinity USB Unlimited Reader and IDE from WB Electronics for this step.

If you have a recent LEIA board with the flashing mode feature, you can simply execute the local flashing script:

sh flash_funcard.sh

This will compile and push the firmware on the funcard inserted in your LEIA board.

Using the testing scripts

Two test scripts are provided here: script-AES128-enc.py and pin_timing_attacks.py.

The testing scripts are mainly Python based, and have been tested with Python3. The dependency requirements for these scripts are:

The smartleia package in its version v1.0.1-1 at least (this contains a small fix for funcards usage through PCSC relay), available here.
The pyscard, numpy and crypto packages, all available with pip.

Two test scripts are provided: script-AES128-enc.py and pin_timing_attacks.py. Each of these scripts can be used in two modes: using LEIA's direct access through /dev/ttyACMx with the toggle USE_LEIA=True as an environment variable, or using PCSC daemon either through a regular smart card reader (or LEIA in PCSC relay mode) by using the toggle USE_LEIA=False as an environment variable:

$ USE_LEIA=False python3 pin_timing_attacks.py 
[+] Using PCSC reader
...
$ USE_LEIA=True python3 pin_timing_attacks.py 
[+] Using LEIA raw access
...

Thescript-AES128-enc.py tests AES-128 encryption and decryption APDUs: this can be a basis to mount some side-channel attacks on an unprotected AES (NOTE: although some APDUs setting masks are present, these are not used and are here for future evolutions).

The pin_timing_attacks.py extracts a secret PIN from the programmed funcard using a timing attack that exploits the dummy algorithm used to check the PIN. In order for this attack to succeed, a timing oracle is needed. Since such a timing oracle exploits variations of less than milliseconds, a proper time measurement for APDUs is necessary. This script shows that LEIA's timing feature can be of use here: a regular smart card reader is not able to extract the secret (at least with the basic approach used using LEIA). You can test LEIA's timing extraction with the USE_LEIA=True, and PCSC based (using a regular reader or LEIA in PCSC mode) using the USE_LEIA=False toggle. The first one should extract the secret PIN successfully, while the second will not succeed.

Handling the ATMega8515 internal triggers

For additional measurement precision, two dedicated triggers have been implemented in the ATMega8515 firmware on the ISO7816-2 pins C4 and C8 (see the figure below). Beware that the C8 pin is shared with LEIA's onboard own trigger.

These two pins are unused by the ISO7816-3 layer, and since they are connected to internal pins of the ATMega8515 (PB5 and PB7), we can use them without perturbing the APDU communication with a reader (either LEIA or any reader).

Two modes are proposed. In the first mode, the pins C4 and C8 are set high just before executing the AES, and set low after its execution. In the second mode, the pins C4 and C8 are toggled at each AES round in order to isolate on the scope each round for a better focus on the points of interest. You can play around with the trig_high_c4/8(), trig_low_c4/8() and trig_inv_c4/8() functions calls inside the AES (it is safe to call them from C and assembly).

      -------------+------------- 
     |   C1        |         C5  | 
     |             |             | 
     +-------\     |     /-------+ 
     |   C2   +----+    +    C6  | 
     |        |         |        | 
     +--------|         |--------+ 
     |   C3   |         |    C7  | 
     |        +----+----+        | 
     +-------/     |     \-------+ 
     |   C4=TRIG1  |    C8=TRIG2 | 
     |             |             | 
      -------------+-------------

By default, the internal triggers are not active. You can specifically activate each one of them using the 00 20 00 00 02 XX YY APDU (class 0x00 and instruction 0x20, with P1 and P2 set to 0x00 and two bytes data). XX=0x01 will activate the first trigger mode on C4 (trig C4 high when AES begins, low after). XX=0x02 will activate the second trigger mode on C4 (toggle C4 at each AES round). XX=0x00 will deactivate the trigger on C4. The same logic holds independently for the second pin C8 using the valye YY.

You can get the actual current values of the triggers modes with the 00 21 00 00 02 APDU, getting two bytes from the card representing the current mode on C4 and C8 respectively.

WARNING: using the internal trigger C8 can perturb LEIA's own trigger set through the dedicated trigger strategies. So use this internal trigger with care and if you know what you are doing!

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