Free laundry for everybody :)

Where I live, there is a room with the laundry machine. Once every other week, you can use it to wash your clothes.
We have different systems to pay: (pseudo) smart card, coins, etc, it depends on where you live. In my case, it was a pseudo smart card you have to refill with money (to the concierge) every time it gets empty.

Here is how it looks like:

I use the word "pseudo" smart card, because as you can see, it is not really one. Actually, there are only 6 contacts (instead of 8) and there is a sort of bus driving the signal somewhere in the white plastic.

The white plastic was heavily attached to the card, so to remove it, I put the whole card in an acetone bath. After few minutes, I was able to remove it without any pain.

I was amazed to see a simple EEPROM underneath. It already meant that replay attacks were possible, even if we didn't know how to interpret the content: save the content, do your laundry and restore the content afterward.

We can identify the chip and deduce from the logo that the manufacturer is "National":

71AR
93C46
M8

I found a similar datasheet. However, we'll see that it is not exactly the same.
Since I didn't want to be invasive on the card, I bought a "season 2 interface". This device is usually used by satellite pirate and is handy to do MITM on smartcards. I got mine for 8€.

I also soldered 8 pins on the back of the interface, to inject my signals (I/O of the SPI).

Since we have the datasheet, we can make the pin ring with a multimeter and deduce what corresponds to what on the smart card contacts:

X --- X (not assigned)
Di --- Sk
Do --- CS
GND --- VCC

I'll make a long story short, because I had different, not really relevant issues. To inject the signal, I used the "Bus pirate" (BP) and to verify that the injected signal was correct, I used the OpenBench Logic Analyzer (OLA). The BP is a cool piece of hardware, because there is an interpreter that will help you to send the correct signal with the correct synchronization, so no need to write a program for it. Since I was not mastering it, I used the OLA to make sure the signal was correct. According to the datasheet, the sequence to send is 0y110 + 6 bit address. After some trial and error, I finally was able to dump the whole memory, by sending something like the following command in raw3wire mode, 5V:

]-^^_^ _^:6 r:1024[

Actually, by looking at the longest prefix, we figure out that the memory is 128 B long and looks like the following:

READ:
0x03 0xE8 0x03 0xC8 0x03 0xD7 0x02 0xE9 0x00 0x00
0x00 0x04 0x03 0xEA 0x0B 0x5E 0x01 0xAA 0x0B 0x5E
0x00 0x00 0x0B 0x5E 0x00 0x00 0x00 0x00 0x00 0x00
0x03 0xE8 0x00 0x04 0x03 0xEA 0x0B 0x5E 0x01 0xAA
0x0B 0x5E 0x0B 0x5E 0x00 0x00 0x00 0x00 0x00 0x00
0x25 0xAE 0x15 0xB3 0x1A 0x0A 0x00 0x00 0x00 0x00
0x00 0x00 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF
0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF
0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF
0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF
0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF
0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF
0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF

The smallest granularity is 2B when accessing the card (just make the division and it'll fit). At the first look, I don't know what these values really are. So I decided to go to the laundry room, put my card in the reader and pay for a wash. The price was 3.-. Then I dumped the content again and made a diff:

READ:
0x03 0xE8 0x03 0xC8 0x03 0xD7 0x02 0xE9 0x00 0x00
0x00 0x04 0x03 0xEA 0x0A 0x32 0x01 0xAA 0x0A 0x32
0x00 0x00 0x0A 0x32 0x00 0x00 0x00 0x00 0x00 0x00
0x03 0xE8 0x00 0x04 0x03 0xEA 0x0A 0x32 0x01 0xAA
0x0A 0x32 0x0A 0x32 0x00 0x00 0x00 0x00 0x00 0x00
0x25 0xAE 0x15 0xB3 0x1A 0x0A 0x00 0x00 0x00 0x00
0x00 0x00 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF
0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF
0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF
0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF
0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF
0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF
0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF

This is interesting, 6 regions in memory changed somehow. But what does 0x0A32 means ? This is 2610, and previously, we had 0x0B5E which are 2910. Remember I told you it costed me 3.-... and what I didn't tell you was the amount of money remaining on my card: 29.10.-. So it is just written in clear in 6 different regions in memory, I couldn't believe it !

The next step was to write 9990 (0x2706) in these memory position and see if it worked. However, to write, according to the datasheet, we have to set WEN, and we just cannot, since all the pinouts are taken. Thus, this is not the good method. I tried to send a "write" command, but without any success :(.

When I was looking for the datasheet of the chip, I found also this one. This is an Atmel, but it turns out the protocol is quite similar. We see there is a "Write Enable", with sequence 0y10011XXXX that has to precede every programming mode.
If we now send a command like

]-^_^^-^^^^^^^^[ ]-^_^-^ -^^^^^^ 0x12:2[ ]-^^_^ -^^^^^^ r:128[

the magic occurs and we see, hopefully, that the content has been correctly written to the EEPROM. This is a good news, so we can now modify the 6 areas we previously found. I did a small script to calculate the offsets, but basically, we need to modify by doing this:

]-^_^^-^^^^^^^^[ ]-^_^-^ _^^^-^^^ 0x27 0x06[ : 7th word
]-^_^^-^^^^^^^^[ ]-^_^-^ _^^-^_^^-^ 0x27 0x06[ : 9th word
]-^_^^-^^^^^^^^[ ]-^_^-^ _^^-^_^-^^ 0x27 0x06[ : 11th word
]-^_^^-^^^^^^^^[ ]-^_^-^ _^-^_^^-^_^ 0x27 0x06[ : 18th word
]-^_^^-^^^^^^^^[ ]-^_^-^ _^-^_^-^_^^ 0x27 0x06[ : 20th word
]-^_^^-^^^^^^^^[ ]-^_^-^ _^-^_^-^_^-^ 0x27 0x06[ : 21th word

Of course, this can be written in a shorter manner, but for clarity, I leave it this way. To sum up, we just modified the 6 areas in memory to put 9990 (0x2706) in them (99.90 CHF), because it sounded like the mechanism was working this way. Now, let's go back to the laundry room to see if it works as expeced:

This is a very small hack, but still nice. I'm not sure this company is still selling this kind of "smart cards", they probably replaced them with real smart cards nowadays. I wouldn't have done this hack without the help of Ian & Sjaak from the dangerous prototypes forum, so greetz to them.