mask-pii (Elixir)

Version: 0.2.0

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

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.
Customizable: Change the masking character (default is *).
Zero Unnecessary Dependencies: Pure Elixir implementation.

Installation

Add :mask_pii to your dependencies:

# mix.exs
{:mask_pii, "~> 0.2.0"}

Then fetch dependencies:

mix deps.get

From a local checkout:

mix deps.get
mix deps.compile

Usage

alias MaskPII.Masker

masker =
  Masker.new()
  |> Masker.mask_emails()
  |> Masker.mask_phones()
  |> Masker.with_mask_char("#")

input_text = "Contact: alice@example.com or 090-1234-5678."
output = Masker.process(masker, input_text)

IO.puts(output)
# => "Contact: a####@example.com or ###-####-5678."

Configuration

The Masker module uses a builder-style API. By default, Masker.new() performs no masking (pass-through).

Builder Functions

Function	Description	Default
`mask_emails/1`	Enables detection and masking of email addresses.	Disabled
`mask_phones/1`	Enables detection and masking of global phone numbers.	Disabled
`with_mask_char/2`	Sets the character used for masking (e.g., `"*"`, `"#"`, `"x"`).	`"*"`

Masking Logic Details

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.
Examples:
- 090-1234-5678 -> ***-****-5678
- +1 (800) 123-4567 -> +* (***) ***-4567
- 12345 -> *2345