Blog Home

ISO8583 payments message format, programmers guide

Posted on 13th Dec 2018 9985 views

There is plenty of documentation about ISO8583 out there on Wikipedia, so making that again does not make sense. However, I want to have a different approach, more pragmatic and more programmatic.


1 What it is

An ISO8583 message is, from a developer's point of view, a TCP/IP message containing a number of bytes. Given that is it a TCP/IP message, it will have 2 bytes of data at the beginning, to specify the length of the message to follow. Then the message, with the length as specified in the 2-byte header. We will refer to this body as the message, from here on.

2 How it looks

It looks like an array of bytes. After the 2-byte TCP header mentioned above, the message starts. 
From here on, we expect this structure of data:
1. A fixed-length header split into several fields, and this is optional. The documentation should specify it, if it exists.
2. A bitmap of 16 bytes, in general. This bitmap is a 8, 16, or 32 byte array which needs to be converted into its binary form. We end up with a binary array like 01101010010001...  Later I will tell you how to read it.
3. A succession of fields usually called "Data Elements", numbered from 2 to 128 , which, as the name says, carry the data of the message.
That's it, this is how the message looks like in its most common form, and it ends after the length specified by the TCP header.

3 How you read ISO8583 messages from the network

1. You read the TCP header, 2 bytes. That tells you how many bytes to read in the message, like 552 bytes.
2. Read the 552 bytes of data, parse the message.
3. Repeat steps 1-2 forever;

4 How you parse ISO8583 messages

We are talking about the 552 bytes in the example above. You start parsing that info.
1. Header - it is optional and fixed length. If it exists, you need to read a fixed number of bytes into it, like 10 bytes. This usually does not exist.
2. Message Type. Fixed length, 4 bytes, most of the time. Read that.
3. Bitmap. It is fixed length 16 bytes, most of the time. Read that, get the binary value. Interpret it according to the paragraph below. This will tell us to read fields 2, 3, 4, 7, 8, 11, 12, 18, ....
4. Read the fields of the message, the ones specified by the bitmap, like the example above.
That is it you get the data in the fields. 

5 Reading the bitmap of the message

Let's say you have this bitmap array that you obtain by converting the bitmap bytes read, into its binary representation: 011110010100010001110001111...
Simplistically, you read it like this: 
Position 1, value is zero, means that there will be no field at position 1; 
Position 2, value is one, means that there will be a field at position 2; We must read Field 2
Position 3, value is one, means that there will be a field at position 3; We must read Field 3
Position 4, value is one, means that there will be a field at position 4; We must read Field 4
Position 5, value is zero, means that there will be no field at position 5; 
Position 6, value is zero, means that there will be no field at position 6; 
Position 7, value is one, means that there will be a field at position 7; We must read Field 7
And so it goes until 128.

6. Reading the ISO8583 fields

As we are reading the bitmap above, we know which fields to read or not read.
Read Field 2. We know from the specification document how it looks like. Usually it is LLVAR. This means 2 byte length[LL], and then the value [VAR] so it is like 161234567890123456. We read this as 16 length, followed by the value: 1234567890123456. Done, next.
Read Filed 3. We know from the specification document how it looks like. Usually it is Fixed 6. This means 6 bytes, fixed. Next
Read Field 4. We know from the specification document how it looks like. Usually it is Fixed 12. This means 12 bytes, fixed. Next
Read Field 7. See, we skipped 5 and 6 because the bitmap said they are not present. We know from the specification document how it looks like. Usually it is Fixed 7. This means 7 bytes, fixed. Next
And so we go until Filed 128.

7 Reading the data in the fields

There are a few rather standard formats for each of the 128 fields, and usually the Specification document tells you how to interpret them.
In general, they are one of the following:
1. Fixed length: they specify the characters type and a length:
a Alphabetic characters, A through Z and a through z
n Numeric digits, 0 through 9
p Pad character, space
s Special characters, i.e. other printable
an Alphabetic and numeric characters
as Alphabetic and special characters
ns Numeric and special characters
anp Alphabetic, numeric and pad characters
ans Alphabetic, numeric and special characters
7 (7 is an example number, it can be 55 just as well)The length of the field
2. Defined-Variable length, they have 2-5 (usually) bytes of length, followed by the value
LL Length of variable data element that follows, 01 through 99
LLL Length of variable data element that follows, 001 through 999
LLLLL Length of variable data element that follows, 00001 through 99999
LLLLLL Length of variable data element that follows, 000001 through 999999
3. Some other variations special fields, proprietary or custom to the specification, like Track2 Data or EMV
That is pretty much it, if you have questions, write them below and we will update the article.



Top Read Articles

Read smart card chip data with APDU commands ISO 7816 27292 views

BIN List & Range for MasterCard, Visa, Amex, Diners, Discover, JCB, CUP 20321 views

Deploy, run and generate with neaPay Card Data Generator 11467 views

Run the neaPay ISO8583 simulator 10617 views

ISO8583 payments message format, programmers guide 9986 views

ISO8583 Response Codes for Transaction processing 8863 views

MCC Codes - Merchant Category Codes to use in ISO8583 Field 18 7470 views

ISO8583 message: The list of ISO 4217 currency codes for data elements 49 and 52 7462 views

ISO8583 Message Converter JSON and XML interface specification mapping 7104 views

ISO8583 Message Types for Transaction Processing 6047 views

ISO8583 Processing Codes for Transaction Processing 5949 views

Deploy the neaPay ISO8583 simulator - video guide 5264 views

Create a new test case in the neaPay ISO8583 simulator Video guide 4720 views

Log Files in BASE24 classic 4360 views

BASE24 classic interview questions 3856 views

BASE24 documentation to read 3776 views

Performance testing at 500, 1000 and 1500 TPS 3763 views

BASE24 classic vs BASE24-eps 3689 views

Connect the neaPay ISO8583 Acquirer simulator to your own host or Issuer 3515 views

Asking for defects support for the neaPay products: converter, switch, issuer, simulator 3341 views

ISO8583 converter to JSON XML SQL to HTTP host - message flow - video guide - Part.2 3193 views

Regression Testing in 1 click with instant Analytics and CSV report 3099 views

Load Test enabling and performance testing at 1TPS and 100TPS 3078 views

BASE24 classic screens examples explained 3073 views

Run the neaPay ISO8583 converter to JSON, XML, SQL, in a test environment 2902 views

Card readers supported by neaPay payments simulator, CHIP and NFC 2894 views

ISO8583 converter to JSON XML SQL to HTTP host - start& run - video guide - Part.1 2893 views

Sample Recommended design for an Acquirer test cases suite, Scenarios and Regression 2869 views

ISO8583 converter to JSON XML SQL to HTTP Host - host unavailable - video guide- Part.3 2862 views

Adding your own card to the Payments simulator to test your system 2778 views

Enabling traces in the payments simulator 2775 views

EMV explained for programmers 2775 views

Altering test cases in Excel for the ISO8583 simulator 2773 views

How the fingerprint reader works in the ISO8583 payments simulator 2772 views

Run One, Run Scenario, Run All, Run Load in the neaPay ISO8583 Simulator - Use guide 2771 views

Deploy the neaPay ISO8583 Payments converter in a test environment 2771 views

Changing fields definitions in the ISO8583 simulator and message converter 2770 views

BASE24-eps interview questions 2689 views

BASE24 classic ATM configuration Tutorial in ATD and XPNET with examples 2596 views

Deploy the neaPay HSM simulator in a test environment 2480 views

Cards and Banks Training 2434 views

Deploy the Payments Switch Router in a test environment 2377 views

BASE24 classic cards configuration tutorial with Examples 2245 views

Add extra custom fields to the ISO8583 simulator 2162 views

ISO8583 ATM POS Crypto API integration with exchanges like Coinbase or Binance 2133 views

BASE24-EPS ACI DESKTOP tutorial - Getting started 1964 views

Getting started with BASE24. Compiling your first TAL program 1907 views

BASE24 classic prefix configuration tutorial CPF with examples 1824 views

BASE24 classic tracing of transactions. Audits, configuration, enabling and opening 1715 views

BASE24 classic Institution configuration Tutorial with example 1607 views

BASE24 classic interchange configuration with examples 1590 views

Working with Base24-eps vs BASE24 Classic 1562 views

BASE24 classic balance file configuration PBF with example 1551 views

ACI BASE24 classic automatic extract configuration 1543 views

BASE24 classic routing in IDF 1347 views

Base24-eps how to create journals with esbldjnl 1322 views

Getting started with Base24 development. TAL tutorial 1299 views

BASE24 classic External Message File configuration EMF with examples 1209 views

Getting started with using Prognosis for BASE24 and BASE24-eps 1135 views

First steps with BASE24 Classic 1113 views

What to expect when installing Base24-eps 1048 views

BASE24 classic host configuration tutorial HCF with examples 1047 views

Managing BASE24-eps implementation projects 980 views

PCI compliant with neapay switch 189 views

ISO8583 Message Converter to XML SQL CSV interface specification mapping 25 views

Ask a question, get advice and help


Read related articles - Iso8583

Are you ready to start or need help?

Ready to start your next project with us? Give us a call or send us an email and we will get back to you as soon as possible!

Get a free quote, Ask for details, Get guidance

Contact us

Download and Use the software yourself

Download software

Follow a getting started guide to deploy and use the software

Get started