Checksum result is different between host and card

[afrascoi]

I tried to send a message with a CRC32 code from the java host to the java card. The host creates a checksum and send it with the message to the card and I also created a checksum on the card side. But I got the different results from two sides.
Why?

[mabel]

pls make your question more detailed and show your code firstly.

[afrascoi]

My host code to creates a checksum

Code: Select all

Checksum checksum = new CRC32();
checksum.update(rawData, 0, rawData.length); 
long checksum_value = checksum.getValue();

Create checksum on card

Code: Select all

Checksum checksum = Checksum.getInstance(Checksum.ALG_ISO3309_CRC32, false);
checksum.doFinal(data, (short)0, (short)data.length, checksum_value, (short)0);

But the result differs from what the host creates.

[afrascoi]

I just found that Java CRC32 starts with an initial value 0xFFFFFFFF.
So I set the card to 0xFFFFFFFF, it works. Now both the card and host checksum result is same.

Code: Select all

byte[] ini = new byte[]{(byte)0xFF, (byte)0xFF, (byte)0xFF, (byte)0xFF};
checksum.init(ini, (short)0, (short)ini.length);

The problem was caused by the initial value.

[mabel]

The below is the introduction about Checksum.ALG_ISO3309_CRC32 from javacard API document.

To obtain the PKZIP (also JDKTM java.util.zip.CRC32 class) behavior:
- Initialize with 0xFFFFFFFF via the init() method