NRF52832实现Mifare K1门禁卡模拟的探索_nrf52832 nfc

1. 当 MIFARE Classic 卡接近读卡器的磁场区域时，卡片会接收到读卡器发来的寻卡指令，然后按照防冲突协议发出自己的卡号UID（寻卡过程）。
2. 收到UID 后，读卡器会选择这张卡（选卡过程）。
3. 接着读卡器发出对某一块的认证请求，然后就开始了一个标准的三步认证协议（认证过程）。
4. 卡片产生一个随机数nT 并以明文方式发送给读卡器。
5. 紧接着读卡器发出它的随机数nR和对卡片的应答aR。
6. 最后卡片返回一个对读卡器的应答aT（认证完成）

      选卡的过程和放冲突模式是硬件自动操作的，所以从第三步开始的协议解析、身份认证、数据加密，才是工作难点。

标签对读卡器的认证

crypto1_init(&state, (uint64_t)tc[k].key); //通过密钥初始化 
 
crypto1_word(&state, tc[k].uid ^ tc[k].tag_challenge, 0);//输入UID和标签的随机数 
 
crypto1_word(&state, tc[k].reader_challenge_enc, 1);//读卡器发送的随机数 
 
rresp = prng_successor(tc[k].tag_challenge, 64);//验证标签的随机数和 
 
rresp ^= crypto1_word (&state, 0, 0); 
 
if(rresp == tc[k].reader_response)//验证读卡器的随机数是否和标签发送的数据数一样   
     printf("TAG> Reader is authentic.\n"); 
 
else 
     printf("TAG> Reader is NOT authentic.\n");

读卡器对标签的认证

        crypto1_init(&state, tc[k].key);
        crypto1_word(&state, tc[k].uid ^ tc[k].tag_challenge, 0);
        rchal = crypto1_word(&state, tc[k].reader_challenge, 0);
        rresp = prng_successor(tc[k].tag_challenge, 64);
        rresp ^= crypto1_word (&state, 0, 0);
        tresp = prng_successor(tc[k].tag_challenge, 96);
        tresp ^= crypto1_word (&state, 0, 0);
        if(tresp == tc[k].tag_response)//读卡器验证随机数
            printf("Reader> Tag is authentic.\n");
        else
            printf("Reader> Tag is NOT authentic.\n");

ISO14443 crc校验算法

#define CRC_A 1
#define CRC_B 2
#define BYTE unsigned char
 
unsigned short UpdateCrc(unsigned char ch, unsigned short *lpwCrc)
{
    ch = (ch^(unsigned char)((*lpwCrc) & 0x00FF));
    ch = (ch^(ch<<4));
 
    *lpwCrc = (*lpwCrc >> 8)^((unsigned short)ch << 8)^((unsigned short)ch<<3)^((unsigned short)ch>>4);
    return(*lpwCrc);
}
 
void ComputeCrc(int CRCType, char *Data, int Length,BYTE *TransmitFirst, BYTE *TransmitSecond)
{
    unsigned char chBlock;
    unsigned short wCrc;
 
    switch(CRCType) {
        case CRC_A:
            wCrc = 0x6363; // ITU-V.41
        break;
        case CRC_B:
            wCrc = 0xFFFF; // ISO 3309
        break;
        default:
    return;
    }
    do {
        chBlock = *Data++;
        UpdateCrc(chBlock, &wCrc);
    } while (--Length);
    if (CRCType == CRC_B)
       wCrc = ~wCrc; // ISO 3309
    *TransmitFirst = (BYTE) (wCrc & 0xFF);
    *TransmitSecond = (BYTE) ((wCrc >> 8) & 0xFF);
     return;
}
BYTE BuffCRC_A[] = {  0x53,0x45,0x47,0x47,0x45,0x52,0x20,0x52};
BYTE BuffCRC_B[] = { 0xC8,0xF0,0xD8,0x2E,0x7B};
unsigned short Crc;
BYTE First, Second;
 
int crc_main(void)
{
printf("CRC-16 reference results 3-Jun-1999\n");
 
printf("by Mickey Cohen - mickey@softchip.com\n\n");
printf("Crc-16 G(x) = x^16 + x^12 + x^5 + 1\n\n");
 
printf("CRC_A of [ ");
printf("%02X ",BuffCRC_A[i]);
 
ComputeCrc(CRC_A, BuffCRC_A, sizeof(BuffCRC_A), &First, &Second);
 
 
printf("] Transmitted: %02X then %02X.\n", First, Second);
 
return(0);
}