​Credit and debit card numbers follow specific formats to ensure proper identification and security. Typically, these numbers range from 13 to 19 digits. The first digit, known as the Major Industry Identifier (MII), indicates the card network and industry. The next six to eight digits form the Issuer Identification Number (IIN), identifying the issuing bank. The remaining digits, except the last one, are the individual account identifier. The final digit is a check digit, calculated using the Luhn algorithm to validate the card number. For example, Visa cards start with a 4 and have 16 digits, while American Express cards start with 34 or 37 and have 15 digits.

​The Luhn's algorithm, also known as the "modulus 10" or "mod 10" algorithm, is a simple checksum formula used to validate various identification numbers, such as credit card numbers. Developed by IBM scientist Hans Peter Luhn in 1954, the algorithm helps detect accidental errors in numbers. It works by doubling every second digit from the right, summing the digits of the products, and adding them to the undoubled digits. If the total modulo 10 is zero, the number is valid. While effective at catching common errors, it is not designed to protect against malicious attacks.

1. ISO 8583:
   • Purpose: ISO 8583 is a messaging standard primarily used in the context of financial transaction processing, particularly for credit and debit card transactions. It defines the format and structure of messages used to exchange information related to these transactions.
   • Scope: ISO 8583 focuses on the specific needs of card payments, ATM transactions, and other related financial operations.
   • Usage: ISO 8583 is used by payment networks, banks, and financial institutions to authorize, process, and settle card-based transactions.
2. ISO 20022:
   • Purpose: ISO 20022 is a broader standard used for the development of financial messages and data standards across various financial domains, including payments, securities, trade finance, and more. It aims to provide a standardized and flexible framework for the entire financial industry.
   • Scope: ISO 20022 covers a wide range of financial processes and data elements, and it is not limited to card payments. It can be used for wire transfers, securities trading, cash management, and other financial transactions.
   • Usage: ISO 20022 is increasingly being adopted as a common language for financial messages, both within and between financial institutions and across different financial systems globally.

The relationship between ISO 8583 and ISO 20022 is primarily one of coexistence. They serve different niches within the financial industry. ISO 8583 is highly specific and well-suited for card-based transactions, while ISO 20022 is a broader, more versatile standard meant to standardise messaging and data exchange across various financial domains.
In some cases, organizations may need to interface ISO 8583 messages with ISO 20022 messages, especially when integrating various financial systems, but this integration usually involves mapping data between the two standards to ensure compatibility. While they have different scopes, their coexistence helps facilitate seamless communication and interoperability within the financial industry.

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​MESSAGE TYPEDESCRIPTION
Category 1 MessagesCustomer Payments and Cheques
Category 2 MessagesFinancial Institution Transfers
Category 3 MessagesTreasury markets – foreign exchange, money markets and derivatives
Category 4 MessagesCollections and Cash Letters
Category 5 MessagesSecurities Markets
Category 6 MessagesTreasury markets – precious markets and syndications
Category 7 MessagesDocumentary Credits and Guarantees / Standby Letters of Credit
Category 8 MessagesTravellers Cheques
Category 9 MessagesCash Management and Customer Status
Category 0 MessagesFIN System Messages