记录Java Card小程序中的所有APDU

Question

Is it possible to save all APDU commands sent to a Java Card applet inside that applet?

For instance: terminal sends 00 B2 01 0C 00 , I want to save it somewhere inside my applet in order to be able to analyse it later.

Answer 1

Sure that's possible. It is required to generate a persistent buffer of some kind. There are various tricks to do this.

The easiest one is to generate a list, where each node holds an new array in which you copy the command. Simply determine the command size first, then copy everything in. Don't forget to copy in the Le bytes for type 2 and type 4 commands.

Probably the best method is to generate a huge array and copy each and every command to it. Persistent arrays are simply fields generated using new byte[size] . Note that the maximum size of the array is 32 Ki - 1You may want to store the size of the command before the command or in a separate persistent array.

As the amount of on card persistent storage is usually pretty minimal you may want to generate some kind of cyclic buffer, where you reuse or overwrite the oldest commands. Mind that there is often no garbage collection possible and if it exists it usually only runs during startup and it may take a long time.

You can immediately copy the header in the process method of the applet. You should only copy the rest of the command data once you receive the bytes, eg after using setIncomingAndReceive and finally setOutgoing / setOutgoingAndSend for the Le byte(s).

Finally you need some command to read out the log as well. Note that a command can be 4 + 1 + 255 + 1 = 262 bytes if you include the Le byte. A command response only holds 256 bytes + the status word. So you may need to read it out in multiple parts, eg using a counter to indicate the specific APDU and offset.

Extended length APDU's deserve a chapter all in themselves, so I'll leave them out for now.

---

I'll also leave the actual implementation as an exercise if you don't mind, you'd probably have an interface such as:

interface APDULogger {
    short logNewCommand(byte[] commandHeader, short commandHeaderOffset);
    void logNc(short nc);
    void logCommandData(byte[] commandData, short commandDataOffset, short commandDataSize);
    void logNe(short ne);
}

and

interface APDURetreiver {
    void retrieveCommand(short history, byte[] commandHeader, short commandHeaderOffset);
    short retrieveNc();
    short retrieveCommandData(byte[] commandData, short commandDataOffset, short maxCommandDataSize);
    short retrieveNe();
}

but mind you, this is just out of the top of my mind. You may want to keep some state too (calling the logNe(short) method signature twice is probably an error).