zig-ipcrypt

A Zig implementation of the IP address encryption and obfuscation methods specified in the ipcrypt document ("Methods for IP Address Encryption and Obfuscation").

Overview

This library implements three variants of IP address encryption as specified in the ipcrypt draft:

1. Deterministic (Deterministic): Format-preserving encryption using AES-128
2. Non-deterministic with KIASU-BC (DeterministicNd): Uses an 8-byte tweak
3. Non-deterministic with AES-XTS (DeterministicNdx): Uses a 16-byte tweak

Tradeoffs

Each variant offers different tradeoffs between security, performance, and format preservation:

Deterministic

• Pros:
  • Format-preserving (output is a valid IP address)
  • Smallest output size (16 bytes)
  • Fastest performance (single AES-128 operation)
• Cons:
  • Reveals repeated inputs (same input always produces same output)
  • No protection against correlation attacks

Non-deterministic with KIASU-BC

• Pros:
  • Resists correlation attacks (same input produces different outputs)
  • Moderate output size (24 bytes)
  • Good performance (AES-128 with tweak modification)
• Cons:
  • Not format-preserving
  • 8-byte tweak has lower collision resistance than 16-byte tweak
  • Birthday bound of 2^32 operations per (key,ip)

Non-deterministic with AES-XTS

• Pros:
  • Resists correlation attacks
  • Highest collision resistance (16-byte tweak)
  • Birthday bound of 2^64 operations per (key,ip)
• Cons:
  • Not format-preserving
  • Largest output size (32 bytes)
  • Requires two AES-128 keys
  • Slightly slower performance (two sequential AES operations)

Key and Tweak Sizes

Usage

Deterministic Encryption

const ipcrypt = @import("ipcrypt");

// Initialize with a 16-byte key
const key = [_]u8{0x2b} ** 16;
const deterministic = ipcrypt.Deterministic.init(key);

// Convert IP address to Ip16 format
const ip = try ipcrypt.Ip16.fromString("192.0.2.1");

// Encrypt
const encrypted = deterministic.encrypt(ip);

// Decrypt
const decrypted = deterministic.decrypt(encrypted);

Non-deterministic Encryption (KIASU-BC)

const ipcrypt = @import("ipcrypt");

// Initialize with a 16-byte key
const key = [_]u8{0x2b} ** 16;
const nd = ipcrypt.DeterministicNd.init(key);

// Convert IP address to Ip16 format
const ip = try ipcrypt.Ip16.fromString("2001:db8::1");

// Encrypt with random tweak
const encrypted = nd.encrypt(ip);

// Encrypt with specific tweak
const tweak = [_]u8{0x2b} ** 8;
const encrypted_with_tweak = nd.encryptWithTweak(ip, tweak);

// Decrypt
const decrypted = nd.decrypt(encrypted);

Non-deterministic Encryption (AES-XTS)

const ipcrypt = @import("ipcrypt");

// Initialize with a 32-byte key
const key = [_]u8{0x2b} ** 32;
const ndx = ipcrypt.DeterministicNdx.init(key);

// Convert IP address to Ip16 format
const ip = try ipcrypt.Ip16.fromString("2001:db8::1");

// Encrypt with random tweak
const encrypted = ndx.encrypt(ip);

// Encrypt with specific tweak
const tweak = [_]u8{0x2b} ** 16;
const encrypted_with_tweak = ndx.encryptWithTweak(ip, tweak);

// Decrypt
const decrypted = ndx.decrypt(encrypted);

Building

Add this to your build.zig.zon:

.{
    .name = "ipcrypt",
    .url = "https://github.com/yourusername/zig-ipcrypt/archive/refs/tags/v0.1.0.tar.gz",
    .hash = "1220...",
}

Then in your build.zig:

const ipcrypt = b.dependency("ipcrypt", .{
    .target = target,
    .optimize = optimize,
});
exe.addModule("ipcrypt", ipcrypt.module("ipcrypt"));

License

ISC License

References

• ipcrypt specification
• AES-128
• KIASU-BC
• AES-XTS