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ISO8583.md

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ISO 8583

Consists of the following

  • header
  • MTI
  • bitmap
    • primary
    • secondary
  • data elements

header

  • it is network specific [Visa, Mastercard], and shows Institution Identification Codes (IICs)
  • example of a header is 0158 which depicts the content of the message (mti+bitmap+data elements) is 158 bytes

MTI

  • message type indicator includes which version of ISO 8583 [1987, 1993, and 2003] is being used, as well as the message class, the message function and the message origin
  • applications use the Message Type Indicator to determine whether the message requires a response and the format of the response
  • 4 digits
    • Digit 1 indicates the version of ISO 8583
    • Digit 2 indicates the class of the message
    • Digit 3 indicates the function of the message
    • Digit 4 indicates who initiated the communication
  • example 0110
    • 0xxx → version of ISO 8583 (0 = 1987 version)
    • x1xx → class of the message (1 = authorization message)
    • xx1x → function of the message (1 = response)
    • xxx0 → who began the communication (0 = acquirer)
  • This means that MTI 0110 is an authorization response message stating that the actual financial transaction was originated by the acquirer.

bitmaps

  • indicates whether there are other data elements or data element sub-fields somewhere else in the message
  • primary bitmap specifies whether fields 1 – 64 are present
  • secondary bitmap in the message, it indicates whether fields 65 – 128 exist
  • example
    • given bitmap 70 10 00 11 02 C0 48 04

      • 70 (hex) to binay is -> 0111 0000

        • 0111 0000 has 8 fiels [field 1 to field 8]
        • counting from left:
          • field 1 is not present because value is 0
          • fields 2,3,4 are present because value is 1

      • 10 (hex) to binay is -> 0001 0000

        • 0001 0000 again has 8 fields [field 9 to 16]
        • counting from left:
          • fields 9,10,11 are 0 meaning they are not present
          • this message shows field 12 is present

      • 00 -> binary = 0000 0000

        • means no fields are present in fields 17 - 24

      • 11 -> binary = 0001 0001

        • has 8 fields [field 25 to 32]
        • this part means fields 28 and 32 are present

      • 02 -> binary = 0000 0010

        • has fields [ field 33 to 40]
        • this part means field 39 is present

      • C0 -> binary = 1100 0000

        • fields 41 - 48
        • means fields 41 and 42 are present

      • 48 -> binary = 0100 1000

        • fields 49 - 56
        • means 50 and 53 are present

      • 04 -> binary = 0000 0100

        • fields 57 - 64
        • means field 62 is present

data elements

  • Message data elements are defined by the ISO 8583 protocol, and each individual data element contains the information for that specific transaction and each has a specified meaning
  • The data elements and code values relating to the transaction, includes amounts, times, dates, and country codes
  • example
    • Bit value 2 is assigned to primary account number, Bit 3 is assigned to processing code, Bit 4 is for transaction amount, etc
    • x + n Numeric (amount) values, where the first byte is either 'C' to indicate a positive or credit value, or 'D' to indicate a negative or Debit value, followed by the numeric value (using n digits)
  • Binary Data
    • In data structures, packed binary data usually signifies that there are more bit combinations used to encode the message
    • unpacked signifies that some bit combinations remain unused
    • ISO 8583 defines two different encoding methods
      • Packed - or 8 bytes of data
      • Unpacked - or 16 bytes as hexadecimal characters

Processing code

The following is a table specifying the message type and processing code for each transaction type

Transaction Message Type Processing Code
Authorization 0100 00 a0 0x
Balance Enquiry 0110 31 a0 0x
Sale 0200 00 a0 0x
Cash 0200 01 a0 0x
Credit Voucher 0200 20 a0 0x
Void 0200 02 a0 0x
Mobile topup 57 a0 0x

Service entry mode values

The Point Of Service (POS) entry mode value has 2 parts

  • PAN entry mode value - the first 2 digits
  • PIN entry capability - the third digit

img.png

Credit Card Issuer Response Codes

An authorization request on a credit card can be denied for a variety of reasons, often with a different financial request issuer response on each occasion.

The following table shows response codes and their meanings for ISO 8583-1987, later versions uses 3 and 4 digit response codes.

img.png

How are messages processed ?

ISO 8583 financial messages consist of a request/response message which is sent between two parties to process the financial transaction. A TCP or other connection type such as:

  • UDP
  • X.25
  • SDLC
  • SNA
  • ASYNC
  • QTP
  • SSL
  • HTTP
  • or another custom connection is opened between the two partie