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How to decode Tag-Length-Value Quickly

Basically, in TLV, the format is Tag, Length, and Value. In the list of protocols, TLV is one of the types. Transmitting the data depends on the protocol you used. However, many financial transactions still follow the TLV format.

According to IBM, TLV data is three parts. The tag tells what type of data it is. The length field has a length of the value. The Value field has actual value.


Tag Length Value TLV Ideas to decode Quickly

Structure of TLV.

TLV comprises three field values. 

  1. Tag
  2. Length
  3. Value

EMV formulated different tags. They have their own meanings. Usually, the Tag and Length together takes 1 to 4 bytes.


The Best example for TLV.

In the below example, you can find the sample TAG, LENGTH, and VALUE fields.


[Tag][Value Length][Value] (ex. "9F4005F000F0A001")
where

Tag Name = 9F40

Value Length (in bytes) = 05 

Value (Hex representation of bytes. Example, "F0" – 1-byte) = F000F0A001

In the above message, tag 9F40 has some meaning designed by EMV company. Here you can find a list of EMV Tags.

How to read the TLV

Tag: 1 or 2 bytes

Length: Length of the Value.

F0-00-F0-A0-01  ==> 5 Bytes

The 'F0', for example, is the HEX value of length '1' byte. So the total length of the value '5' bytes.


References

  1. Tag Length Value Wiki Tutorial
  2. List of all EMV Tags

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