java - 带身份验证的 NTAG212 Mifare Ultralight

Question

我是 NFC Android 的新手，几天来我一直在尝试获取 NTAG212 Mifare Ultralight with Authentication 的第 4 页到第 7 页，我已经有了 PWD 和 PACK 来执行 < strong>PWD_AUTH 基于 NTAG212 文档。

我采用这种方法...

//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
    }
}

我总是收到 android.nfc.TagLostException: Tag was lost. 向 NFC 发送 PWD_AUTH 命令后出错。有人可以告诉我我做错了什么吗？我的方法正确吗？请帮忙。

注意:我已经多次阅读 NTAG212 的文档，搜索了 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 字节值)，如果您使用正确的密码进行身份验证，标签将以其密码确认 (PACK) 值(一个 2 字节值)进行响应。然后，您可以根据预期的密码确认 PACK 值以“验证”标签。

所以正确的命令是:

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条件(在 NTAG212 上):

1. 将 PWD(第 39 页)设置为您想要的密码(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]
   });
   

2. 将 PACK(第 40 页，字节 0-1)设置为您想要的密码确认(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
   });
   

3. 将 AUTHLIM(第 38 页，字节 0，位 2-0)设置为密码验证尝试失败的最大次数(将此值设置为 0 将允许无限次 PWD_AUTH 尝试)。

4. 将 PROT(第 38 页，字节 0，位 7)设置为您想要的值(0 = PWD_AUTH 仅用于写入访问，1 = PWD_AUTH 是读取和写入访问所必需的)。

   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)
       });
   }
   

5. 将 AUTH0(第 37 页，字节 3)设置为需要密码验证的第一页。

   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标签技术，除了直接使用transceive方法，还可以使用readPages和writePage 方法:

• 读命令

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

  相当于

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

• 写命令

  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]
  });
  

  相当于

  nfc.writePage(pageAddress, data);