ISO8583 payments message format, programmers guide

Posted on 13th Dec 2018 17480 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.

 


LinkedIn

Docs Home ISO8583 Simulator Tutorials ISO8583 Converter Cards Issuer BASE24 Base24-eps Reference Guide ISO8583 Switch HSM Simulator POS Simulator


Top Read Articles


BIN List & Range for MasterCard, Visa, Amex, Diners, Discover, JCB, CUP
149396 views

Read smart card chip data with APDU commands ISO 7816
59864 views

ISO8583 Response Codes for Transaction processing
55941 views

ISO8583 Message Types for Transaction Processing
28227 views

ISO8583 Processing Codes for Transaction Processing
27817 views

Run the neaPay ISO8583 simulator
19844 views

Deploy, run and generate with neaPay Card Data Generator
19739 views

MCC Codes - Merchant Category Codes to use in ISO8583 Field 18
18678 views

ISO8583 payments message format, programmers guide
17481 views

ISO8583 message: The list of ISO 4217 currency codes for data elements 49 and 52
15955 views

ISO8583 Message Converter JSON and XML interface specification mapping
12880 views

Cards and Banks Training
12462 views

Support for the neaPay products: Authorization, Switch, Converter, Simulator, Issuer
9149 views

Log Files in BASE24 classic
8950 views

Create a new test case in the neaPay ISO8583 simulator Video guide
8578 views

Java version for neapay products Simulator Converter Switch Authorization Cards Issuer
8155 views

Deploy the neaPay ISO8583 simulator - video guide
8120 views

BASE24 classic vs BASE24-eps
7908 views

BASE24 documentation to read
7840 views

BASE24 classic interview questions
7688 views

Performance testing at 500, 1000 and 1500 TPS
7552 views

EMV explained for programmers
7351 views

ISO8583 converter to JSON XML SQL to HTTP host - message flow - video guide - Part.2
7103 views

ISO8583 ATM POS Crypto API integration with exchanges like Coinbase or Binance
6780 views

Adding your own card to the Payments simulator to test your system
6597 views

ISO8583 converter to JSON XML SQL to HTTP Host - host unavailable - video guide- Part.3
6531 views

Card readers supported by neaPay payments simulator, CHIP and NFC
6520 views

Connect the neaPay ISO8583 Acquirer simulator to your own host or Issuer
6511 views

ISO8583 converter to JSON XML SQL to HTTP host - start& run - video guide - Part.1
6492 views

Run the neaPay ISO8583 converter to JSON, XML, SQL, in a test environment
6372 views

Load Test enabling and performance testing at 1TPS and 100TPS
6357 views

Changing fields definitions in the ISO8583 simulator and message converter
6350 views

Altering test cases in Excel for the ISO8583 simulator
6348 views

Deploy the neaPay ISO8583 Payments converter in a test environment
6343 views

Sample Recommended design for an Acquirer test cases suite, Scenarios and Regression
6342 views

How the fingerprint reader works in the ISO8583 payments simulator
6341 views

Run One, Run Scenario, Run All, Run Load in the neaPay ISO8583 Simulator - Use guide
6340 views

Enabling traces in the payments simulator
6339 views

BASE24 classic screens examples explained
6336 views

Regression Testing in 1 click with instant Analytics and CSV report
6207 views

Deploy the neaPay HSM simulator in a test environment
6065 views

BASE24-eps interview questions
6016 views

Deploy the Payments Switch Router in a test environment
5922 views

BASE24 classic ATM configuration Tutorial in ATD and XPNET with examples
5671 views

Add extra custom fields to the ISO8583 simulator
5504 views

BASE24 classic cards configuration tutorial with Examples
5321 views

PCI compliant with neapay switch
5103 views

BASE24-EPS ACI DESKTOP tutorial - Getting started
4915 views

ISO8583 Message Converter to XML SQL CSV interface specification mapping
4757 views

Trace configuration in neaPay Simulator, Converter, Switch, Authorization and Cards Issuer
4551 views

BASE24 classic prefix configuration tutorial CPF with examples
3656 views

BASE24 classic tracing of transactions. Audits, configuration, enabling and opening
3551 views

ACI BASE24 classic automatic extract configuration
3379 views

BASE24 classic Institution configuration Tutorial with example
3227 views

BASE24 classic balance file configuration PBF with example
3188 views

First steps with BASE24 Classic
2960 views

Getting started with using Prognosis for BASE24 and BASE24-eps
2723 views

POS simulator format SPDH HPDH Verifone and custom
2514 views

Iso8583 - articles


Are you ready to start or need help?

 

Download and Use the software yourself


Download software

Read Documentation and Start guides


Get started