android – 如何解释Mifare Classic 1K上的NDEF内容

解决方法@H_450_18@

首先,在这两个应用笔记中指定了NXP针对mifare Classic标签的专有NDEF映射：

> NFC Type MIFARE Classic Tag Operation
> MIFARE Classic as NFC Type MIFARE Classic Tag

正如您已经发现的那样(Unable to authenticate to a MIFARE Classic tag used as NDEF tag),NDEF数据存储在某些扇区的数据块中(NDEF扇区,通过MIFARE Application Directory标记).因此,与NDEF相关的数据是来自这些块的所有数据的组合.

例如.如果您的NDEF扇区是扇区1和2,则需要读取块4,5,6(=扇区1的块0..2)和块8,9,10(=扇区2的块0..2)聚合NDEF标签的数据.

在您的情况下,来自块4和5的数据似乎已足够(因为标记数据的结尾在块5中标记,正如您自己正确找到的那样).您的案例中的相关标签数据是

0000030E D1010A54 02656E6D 6F726574
746FFE00 00000000 00000000 00000000

标签数据本身被打包到TLV(标签长度值)结构中. TLV块由强制标记字节,条件长度字段和可选数据字段组成：

>没有长度和数据字段的TLV：

+----------+
| TAG      |
| (1 bytE) |
+----------+

> TLV,其中数据字段的长度为0到254字节：

+----------+----------+-----------+
| TAG      | LENGHT n | DATA      |
| (1 bytE) | (1 bytE) | (n bytes) |
+----------+----------+-----------+

> TLV,其中数据字段的长度为255到65534字节：

+----------+----------+-----------+-----------+
| TAG      | 0xFF     | LENGHT n  | DATA      |
| (1 bytE) | (1 bytE) | (2 bytes) | (n bytes) |
+----------+----------+-----------+-----------+

您特定情况下的有趣标签是：

> NULL TLV：Tag = 0x00,没有长度字段,没有数据字段
>终结者TLV：Tag = 0xFE,没有数据字段
> NDEF消息TLV：Tag = 0x03,有字段,有数据字段(虽然可能有零长度)

因此,在您的情况下,数据解码为：

00    NULL TLV (ignore,process next bytE)
00    NULL TLV (ignore,process next bytE)
03    NDEF message TLV (contains your NDEF messagE)
    0E                              Lenght = 14 bytes
    D1010A5402656E6D6F726574746F    Data = NDEF message
FE    Terminator TLV (stop processing the data)

NDEF消息可以包含0个,1个或更多NDEF记录.在您的情况下,NDEF消息解码为以下内容：

D1    Record header (of first and only record)
          Bit 7 = MB = 1: first record of NDEF message
          Bit 6 = ME = 1: last record of NDEF message
          Bit 5 = CF = 0: last or only record of chain
          Bit 4 = SR = 1: short record length field
          Bit 3 = IL = 0: no ID/ID length fields
          Bit 2..0 = TNF = 0x1: Type field represents an NFC Forum
                                well-kNown type name
    01    Type Length = 1 byte
    0A    Payload length = 10 bytes
    54    Type field (decoded according to the setTing of TNF)
              "T" (in US-ASCII) = binary form of type name urn:nfc:wkt:T
    02656E6D6F726574746F    Payload field (decoded according to the value of the Type field)

因此,您的NDEF消息由一个文本记录组成(NFC FOrum众所周知的类型,数据有效负载02656E6D6F726574746F.此记录有效负载解码为：

02    Status byte
          Bit 7 = 0: Text is UTF-8 encoded
          Bit 6 = 0: Not used
          Bit 5..0 = 0x02: Length of IANA language code field
656E    IANA language code field
            "en" (in US-ASCII) = Text is in English
6D6F726574746F    Text
                      "moretto" (in UTF-8)