NTAG212具有认证的Mifare Ultralight

Question

我是新来的NFC Android和我一直在坚持了几天试图获得第4页至第7页 NTAG212的Mifare超轻与验证 ，我已经有PWD和PACK做
PWD_AUTH 基础上， NTAG212 文档。

我这样做

//assume password as array of bytes
//assume pack as array of bytes
try{
nfc.connect();
byte[] cmd1 = nfc.transceive(new byte[]{ (byte) 0x30, (byte) 0x00 }); //read the page 0     to make the NFC active
nfc.transceive(new byte[]{
   (byte) 0x1B, //command for PWD_AUTH
   pass[0],
   pass[1],
   pass[2],
   pass[3]
});
byte[] cmd4 = nfc.transceive(new byte[]{ (byte) 0x30, (byte) 0x04 }); //read the page 4
}catch(TagLostException e){
  e.printStackTrace();
}catch(IOException e){
  e.printStachTrace();
}finally{
    try{
        nfc.close();
    }catch(Exception e){
      //display failed to close
    }
}

android.nfc.TagLostException: Tag was lost.将PWD_AUTH命令发送到NFC后，我总是会收到错误消息。有人可以告诉我我在做什么错吗？我的方法正确吗？请帮忙。

注意：我已经阅读了NTAG212的文档很多次，搜索过google，stackoverflow和所有可能的资源。

TIA，
肯斯特

Answer 1

您发送给标签的PWD_AUTH命令没有多大意义。

PWD_AUTH命令的想法是，您发送密码（一个4字节的值），并且如果您使用正确的密码进行了身份验证，则标签将以其密码确认（PACK）值（一个2字节的值）进行响应。然后，您可以对照预期的密码确认来验证PACK值，以“认证”标签。

因此正确的命令将是：

    byte[] response = nfc.transceive(new byte[] {
        (byte) 0x1B, // PWD_AUTH
        pass[0], pass[1], pass[2], pass[3]
    });
    if ((response != null) && (response.length >= 2)) {
       byte[] pack = Arrays.copyOf(response, 2);
       // TODO: verify PACK to confirm that tag is authentic (not really,
       // but that whole PWD_AUTH/PACK authentication mechanism was not
       // really meant to bring much security, I hope; same with the
       // NTAG signature btw.)
    }

启用密码保护所需的内容（在NTAG212上）：

1. 将PWD（第39页）设置为所需的密码（默认值为0xFFFFFFFF）。

        byte[] response = nfc.transceive(new byte[] {
        (byte) 0xA2, // WRITE
        (byte) 39,   // page address
        pass[0], pass[1], pass[2], pass[3]
    });

1. 将PACK（第40页，字节0-1）设置为所需的密码确认（默认值为0x0000）。

        byte[] response = nfc.transceive(new byte[] {
        (byte) 0xA2, // WRITE
        (byte) 40,   // page address
        pack[0], pack[1],   // bytes 0-1 are PACK value
        (byte) 0, (byte) 0  // other bytes are RFU and must be written as 0
    });

1. 将AUTHLIM（第38页，字节0，位2-0）设置为失败的密码验证尝试的最大次数（将此值设置为0将允许无限制的PWD_AUTH尝试次数）。

2. 将PROT（第38页，字节0，位7）设置为所需值（0 =仅对写访问才需要PWD_AUTH，1 =对读和写访问才需要PWD_AUTH）。

        byte[] response = nfc.transceive(new byte[] {
        (byte) 0x30, // READ
        (byte) 38    // page address
    });
    if ((response != null) && (response.length >= 16)) {  // read always returns 4 pages
        boolean prot = false;  // false = PWD_AUTH for write only, true = PWD_AUTH for read and write
        int authlim = 0; // value between 0 and 7
        response = nfc.transceive(new byte[] {
            (byte) 0xA2, // WRITE
            (byte) 38,   // page address
            (byte) ((response[0] & 0x078) | (prot ? 0x080 : 0x000) | (authlim & 0x007)),
            response[1], response[2], response[3]  // keep old value for bytes 1-3, you could also simply set them to 0 as they are currently RFU and must always be written as 0 (response[1], response[2], response[3] will contain 0 too as they contain the read RFU value)
        });
    }

1. 将AUTH0（第37页，字节3）设置为需要密码认证的第一页。

        byte[] response = nfc.transceive(new byte[] {
        (byte) 0x30, // READ
        (byte) 37    // page address
    });
    if ((response != null) && (response.length >= 16)) {  // read always returns 4 pages
        boolean prot = false;  // false = PWD_AUTH for write only, true = PWD_AUTH for read and write
        int auth0 = 0; // first page to be protected, set to a value between 0 and 37 for NTAG212
        response = nfc.transceive(new byte[] {
            (byte) 0xA2, // WRITE
            (byte) 37,   // page address
            response[0], // keep old value for byte 0
            response[1], // keep old value for byte 1
            response[2], // keep old value for byte 2
            (byte) (auth0 & 0x0ff)
        });
    }

如果使用MifareUltralight标记技术，则transceive可以直接使用readPages和writePage方法，而不是直接使用方法：

• READ命令

        byte[] response = nfc.transceive(new byte[] {
        (byte) 0x30,                  // READ
        (byte) (pageAddress & 0x0ff)  // page address
    });

等价于

        byte[] response = nfc.readPages(pageAddress);

• WRITE命令

        byte[] data = { (byte)..., (byte)..., (byte)..., (byte)... };
    byte[] response = nfc.transceive(new byte[] {
        (byte) 0xA2,                  // WRITE
        (byte) (pageAddress & 0x0ff), // page address
        data[0], data[1], data[2], data[3]
    });

等价于

    nfc.writePage(pageAddress, data);