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ISO8583 Manual disassembly of messages

8583 message is mostly used for data exchange between POS terminal and background acquiring system. Generally, a complete message consists of the following parts:

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Length Header 8583 Data

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The length part is usually two bytes, indicating the total length of the message. ("Header"+"Data", partial length)

TPDU determines the network protocol between terminal and system. TPDU is a 10-bit number.

Some of the messages actually transmitted are represented by ASCII codes and some by BCD codes.

Here is a simple message. I will give you a detailed analysis (according to the POS terminal specification of China UnionPay)

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005f600003000200302044c020c08810210009000000000001005018998802100006

377689200010172645673d130820147800000000303130303030313230313130303

030303130303030303131353626000000000000000011260001100000

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Total message length 95 bytes

TPDU

This is the information type (MTI), which is a four-digit number, here "0200"(request).

When transmitted, it is represented by BCD code as "02h 00h", each of which has its meaning.

First digit: 8583 version number

Second place: message class

Third place: message sub-class

Number 4: Transitions Originator

Here is a detailed explanation of the bitmap:

bitmap fields, indicating which fields exist Bitmaps include basic bitmaps and extended bitmaps

Bitmap analysis using BCD code. Put the BCD code in that position "1", which indicates which fields.

The bitmap is parsed as follows:

0011000000100000010001001100000000100000110000001000100000010000

Count them yourself. The resolved fields are: 3, 4, 11, 18, 22, 25, 26, 35, 41, 42, 49, 53, 60.

The next step is to correspond to the attributes of each domain and start corresponding data.

field 3, transaction processing code, n6, fixed length, represented by a 3-byte BCD code.

field 4, transaction amount, n12, fixed length, expressed by 6 bytes BCD code, where the amount is 0.01 yuan

If it is RMB, the unit of transaction amount is RMB cents.

field 11, serial number, n6, fixed length, expressed by 3 bytes of BCD code, serial number is "005018".

field 18, merchant type, n4, fixed length, represented by a 2-byte BCD code. (Merchant Type Code Industry Query)

field 22, service point input mode, n3, fixed length, define PIN and PAN input mode at the service terminal.

field 25, service point condition code, n2, fixed length, 00 indicates normal trading

field 26, service point PIN acquisition code, n2, fixed length, this field describes the maximum length of personal password plaintext allowed to be entered by the service point device.

field 35, two track data, z.. 37(LLVAR), the first byte indicates the length of the field (37)

The next 19 bytes of BCD code represent track data, and the radix bit is supplemented with 0 or skipped.

field 41, terminal number, ans8, fixed length, ASCII code representation; here the terminal number is: "01000012".

field 42, merchant number, ans15, fixed length, ASCII code representation; merchant number here is: "0110000100001"

field 49, currency code, ans3, fixed length, ASCII code; RMB code: "156".

field 53, safety control information, n16, required if safety requirements exist

field 60, custom fields, an.. 011(LLLVAR); two bytes indicate the length (00 11), left filled with "0".

ISO8583 Message Dismantling Codes See next issue.

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