MIFARE Classic：如何找到良好的访问字节值 [英] MIFARE Classic: How to find to good Access Byte value

问题描述

我的目标是仅具有KEY A身份验证并禁用Key B（用于存储数据的空间）。

我阅读了以下文档：

• 
  
  

  在这里，我只想保留键A（R&写入数据）并停用密钥B。我选择了第一个规则：C1 = 0 C2 = C3 = 0。这样对吗？

  
  
  2. 访问字节规则
  
  
  
  
  

  我只想使用键A，以便能够更改键A的值（写）-访问位：读/写密钥A。因此，我选择了C1 = 0 C2 = 0和C3 = 1。

  
  
  

  最终结果是字节6 = F8，字节7 = 77和字节8 = 80

  
  
  

  当我将这些值写入MIFARE卡时，这是不正确的。

  
  
  

  您能帮我找到好的值吗？

  解决方案

  您选择的访问字节解码为C1 = 7，C2 = 0，C3 = 8，因此您拥有

  
  
  
  
  
  • 部门尾部：C1 ₃ ，C2 ₃ ，C3 ₃ = 0、0、1
  
  
  • 数据块：C1 _0,1,2 ，C2 _0,1,2 ，C3 _0,1,2 = 1、0、0
  
  
  
  
  

  因此，您选择了扇区预告片，可通过键A写入并可读（键除外） A本身具有密钥A。因此，就没有密钥B。因此，对于数据块，这意味着可以用密钥A读取它们，但不能进行写操作（由于缺少密钥B），递增等。 / p>
  
  

  如果只想使用键A进行读/写访问，则可以使用如下所示的东西：

  
  
  
  
  
  • 行业预告片：C1 ₃ ，C2 ₃ ，C3 ₃ = 0、0、1
  
  
  • 数据块：C1 _0,1,2 ，C2 _0,1,2 ，C3 _0,1,2 = 0，0，0
  
  
  
  
  

  这将导致访问字节C1 = 0，C2 = 0，C3 = 8：

    FF 07 80 
    

  
  

  My aim is to have only KEY A authentification and disable Key B (used space to store data).

  I read these documentations:

  • http://www.nxp.com/documents/data_sheet/MF1S503x.pdf
  • http://dangerousthings.com/wp-content/uploads/2012/08/NFC-Access-Control-for-Mifare-S50.pdf

  I understand how to calculate the hexadecimal values of these three bytes.

  But I don't understand how to choose the good data block and access byte rules :

  1. Data Block rule

  Here, I want to keep only key A (R & Write data) and deactivate Key B. I choosed the first rule: C1=0 C2= C3=0. Is this right?

  2. Access byte rule

  I would like to use only key A, to be able to change key A value (Write) - Access bits: Read/Write Key A. So I choosed C1=0 C2=0 and C3=1. Is this correct?

  The final results is Byte 6 = F8, byte 7 = 77 and Byte 8 = 80

  When I write these values into a MIFARE card, it's not correct.

  Could you help me to find the good value?

  解决方案

  The access bytes you chose decode to C1=7, C2=0, C3=8, so you have

  • Sector trailer: C1₃, C2₃, C3₃ = 0, 0, 1
  • Data blocks: C1_0,1,2, C2_0,1,2, C3_0,1,2 = 1, 0, 0

  So you chose the sector trailer to be writable with key A and readable (except for key A itself) with key A. Consequently there is not key B. Thus, for the data blocks this means that they can be read with key A, but no writing (due to missing key B), incrementing, etc. is possible.

  If you want read/write access using only key A, you would use soemthing like the following:

  • Sector trailer: C1₃, C2₃, C3₃ = 0, 0, 1
  • Data blocks: C1_0,1,2, C2_0,1,2, C3_0,1,2 = 0, 0, 0

  Which would result in the access bytes C1=0, C2=0, C3=8:

  FF 07 80
  

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