# Record the process of using pn532 to change the balance of the school’s water card

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1. Preparation process

1.PN532

2. PL2303 serial port module USB to TTL (purchased at amazon)

Install the driver after connecting to the computer.

Pay attention to the line sequence, black, red, white and green, the board will burn if you connect it wrong~~~~

2. Cracking process

The following operations are all done by win10 64-bit operating system

1. Open the PN532 tool, display the found device, and connect the water card to the module

Solution for showing no card found:

Method 1: Check whether the circuit is connected correctly and reconnect

Method 2: View the driver—the picture in the device manager is the driver

Method 3: Use strong light on the water card, and put the chip on top of the module to read

If none of the above three methods are used, your water card does not support it.

2. Read the entire card data

Save the data and get the first group

Use it once, spend a little money to get the second set of data, the two sets of data are compared below, only 14 and 15 rows are different

The first group on the left 86.66 The second group on the right 86.58

3. Start changing money

Here is money

The first group of money: da21 reverse order 21da, convert hexadecimal to decimal 8666

The same for the second group: d221-21d2-8658

Here is the check code, if the check code is calculated incorrectly, the balance is wrong

Check code calculation method:

218+33=251

251-353=-102

The -102 here is the algebra of this algorithm. Bring -102 into the second set of data and see if the results are the same

210+33=243

243–102=345

Here 345 is decimal. Converted from decimal to hexadecimal, 0159 happens to be the number obtained by the second set of check codes. Then -102 is the algebra of this card, so we can change the amount of this water card at will.

Final note: each card has its own algorithm, and each card cycles through the above process

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