---
title: "Anonymize credit card numbers"
url: "https://axoflow.com/docs/axosyslog-core/4.28/chapter-manipulating-messages/modifying-messages/anonymizing-credit-card-numbers/"
last_modified: "2026-09-23T16:42:00+02:00"
---

> For the complete documentation index, see [llms.txt](https://axoflow.com/docs/axosyslog-core/4.28/llms.txt).

# Anonymize credit card numbers

Log messages of banking and e-commerce applications might include credit card numbers (Primary Account Number or PAN). According to privacy best practices and the requirements of the Payment Card Industry Data Security Standards (PCI-DSS), PAN must be rendered unreadable. The AxoSyslog application uses a regular expression to detect credit card numbers, and provides two ways to accomplish this: you can either mask the credit card numbers, or replace them with a hash. To mask the credit card numbers, use the `credit-card-mask()` or the `credit-card-hash()` rewrite rules in a log path.

## Declaration

```shell
@include "scl/rewrite/cc-mask.conf"

rewrite {
    credit-card-mask(value("<message-field-to-process>"));
};
```

By default, these rewrite rules process the MESSAGE part of the log message.

## credit-card-hash()

|  |  |
| --- | --- |
| Synopsis: | `credit-card-hash(value("<message-field-to-process>"))` |

*Description:* Process the specified message field (by default, `${MESSAGE}`), and replace any credit card numbers (Primary Account Number or PAN) with a 16-character-long hash. This hash is generated by calculating the SHA-1 hash of the credit card number, selecting the first 64 bits of this hash, and representing this 64 bits in 16 characters.

## credit-card-mask()

|  |  |
| --- | --- |
| Synopsis: | `credit-card-mask(value("<message-field-to-process>"))` |

*Description:* Process the specified message field (by default, `${MESSAGE}`), and replace the 7-12th character of any credit card numbers (Primary Account Number or PAN) with asterisks (`*`). For example, AxoSyslog replaces the number `5542043004559005` with `554204******9005`.

Last modified September 23, 2026: [Formatting fixes (4b066aca)](https://github.com/axoflow/axosyslog-core-docs/commit/4b066aca197deb5a17c7eb1a56bfae5f8b983172)