mask-pii

Version: 0.2.0

A lightweight, customizable Rust library for masking Personally Identifiable Information (PII) such as email addresses and phone numbers (supporting global formats).

It is designed to be safe, fast, and easy to integrate into logging or data processing pipelines.

🌐 Official website: https://finitefield.org/en/oss/mask-pii
🏢 Developed by: Finite Field, K.K.

Features

📧 Email Masking: Masks the local part while preserving the domain (e.g., a****@example.com).
📞 Global Phone Masking: Detects international phone formats and masks all digits except the last 4 (e.g., 090-****-5678, +1 (***) ***-1234).
🛠 Customizable: Change the masking character (default is *).
🚀 Zero Unnecessary Dependencies: Pure Rust implementation.

Installation

Add this to your Cargo.toml:

[dependencies]
mask-pii = "0.1.0"

Usage

use mask_pii::Masker;

fn main() {
    // Configure the masker
    let masker = Masker::new()
        .mask_emails()
        .mask_phones()
        .with_mask_char('#'); // Optional: Use '#' instead of '*'

    let input = "Contact: alice@example.com or 090-1234-5678.";
    
    // Process the text
    let output = masker.process(input);

    println!("{}", output);
    // Output: "Contact: a####@example.com or 090-####-5678."
}

Configuration

The Masker struct uses the Builder Pattern. You can chain methods to configure which PII types to detect and how to mask them.

By default, Masker::new() performs no masking (pass-through). You must explicitly enable the filters you need.

Builder Methods

Method	Description	Default
`mask_emails()`	Enables detection and masking of email addresses.	`Disabled`
`mask_phones()`	Enables detection and masking of global phone numbers.	`Disabled`
`with_mask_char(char)`	Sets the character used for masking (e.g., `'*'`, `'#'`, `'x'`).	`'*'`

Masking Logic Details

Understanding how data is masked is crucial for security and usability.

📧 Emails
Pattern: Detects standard email formats.
Behavior: Keeps the first character of the local part and the domain. Masks the rest of the local part.
Example: alice@example.com -> a****@example.com
Short Emails: If the local part is 1 character, it is fully masked (e.g., a@b.com -> *@b.com).
📞 Phones (Global Support)
Pattern: Detects sequences of digits that look like phone numbers (supports International +81..., US (555)..., and Hyphenated 090-...).
Behavior: Preserves formatting (hyphens, spaces, parentheses) and the last 4 digits. All other digits are replaced.
Example:
090-1234-5678 -> 090-****-5678
+1 (800) 123-4567 -> +1 (***) ***-4567
12345 -> *2345 (Short numbers)