CRX3 Packer

A Node.js package for packing Chrome extensions into the CRX3 format. This package allows you to create signed .crx3 files from directories or zip files, which can then be distributed as Chrome extensions.

Features

• ✅ Pack directories into CRX3 format
• ✅ Pack zip files into CRX3 format
• ✅ Generate RSA key pairs for signing
• ✅ Command-line interface
• ✅ TypeScript support
• ✅ Follows Chrome Extension CRX3 specification

Installation

npm install crx3-packer

Or install globally for CLI usage:

npm install -g crx3-packer

Quick Start

Programmatic Usage

import { CRX3Packer } from 'crx3-packer';
import * as fs from 'fs';

// Generate a key pair (do this once)
const { privateKey, publicKey } = CRX3Packer.generateKeyPair();
fs.writeFileSync('private.pem', privateKey);
fs.writeFileSync('public.pem', publicKey);

// Pack a directory
const packer = new CRX3Packer();
await packer.packDirectory('./my-extension', {
  privateKey: fs.readFileSync('private.pem', 'utf8'),
  output: './my-extension.crx3'
});

console.log('Extension packed successfully!');

CLI Usage

# Generate a developer key pair
crx3-pack generate-key -o ./keys

# Generate a publisher key pair
crx3-pack generate-key -o ./keys --publisher

# Pack a directory with developer key only
crx3-pack pack -i ./my-extension -o ./my-extension.crx3 -k ./keys/private.pem

# Pack with both developer and publisher keys
crx3-pack pack -i ./my-extension -o ./my-extension.crx3 -k ./keys/private.pem --publisher-key ./keys/publisher-private.pem

# Pack a zip file
crx3-pack pack -i ./my-extension.zip -o ./my-extension.crx3 -k ./keys/private.pem

# Get extension ID from public key
crx3-pack get-crx-id -k ./keys/public.pem

API Reference

CRX3Packer Class

Methods

packDirectory(inputDir: string, options: PackOptions): Promise<void>

Packs a directory into a CRX3 file.

Parameters:

• inputDir - Path to the directory to pack
• options - Packing options (see PackOptions interface)

Example:

await packer.packDirectory('./extension-folder', {
  privateKey: privateKeyString,
  output: './extension.crx3'
});

packZip(zipData: Buffer, options: PackOptions): Promise<void>

Packs zip data into a CRX3 file.

Parameters:

• zipData - Buffer containing zip file data
• options - Packing options (see PackOptions interface)

packFromZipFile(zipPath: string, options: PackOptions): Promise<void>

Packs a zip file into a CRX3 file.

Parameters:

• zipPath - Path to the zip file
• options - Packing options (see PackOptions interface)

Static Methods

generateKeyPair(): { privateKey: string; publicKey: string }

Generates a new RSA key pair for signing extensions (developer keys).

Returns:

• Object with privateKey and publicKey in PEM format (RSA-2048)

Example:

const { privateKey, publicKey } = CRX3Packer.generateKeyPair();

generateEcdsaKeyPair(): { privateKey: string; publicKey: string }

Generates a new ECDSA key pair for publisher signing (P-256 curve).

Returns:

• Object with privateKey and publicKey in PEM format (ECDSA P-256)

Example:

const { privateKey, publicKey } = CRX3Packer.generateEcdsaKeyPair();

getCrxIdFromPublicKey(publicKey: string | Buffer): string

Generates a CRX ID (extension ID) from a public key.

Parameters:

• publicKey - Public key in PEM format or as Buffer

Returns:

• Extension ID as string

PackOptions Interface

interface PackOptions {
  /** Private key for signing (PEM format) */
  privateKey: string | Buffer;
  /** Output path for the .crx3 file */
  output: string;
  /** Optional CRX ID override (will be derived from public key if not provided) */
  crxId?: Buffer;
  /** Optional publisher private key for publisher signatures (ECDSA P-256) */
  publisherPrivateKey?: string | Buffer;
}

CLI Commands

pack

Pack a directory or zip file into CRX3 format.

crx3-pack pack -i <input> -o <output> -k <key> [--publisher-key <publisher-key>] [--crx-id <id>]

Options:

• -i, --input <path> - Input directory or zip file path (required)
• -o, --output <path> - Output CRX3 file path (required)
• -k, --key <path> - Developer private key file path in PEM format (required)
• --publisher-key <path> - Optional publisher private key file path in PEM format
• --crx-id <id> - Optional CRX ID override in hex format

generate-key

Generate a new RSA key pair for signing.

crx3-pack generate-key -o <output> [--publisher]

Options:

• -o, --output <path> - Output directory for key files (required)
• --publisher - Generate publisher key pair instead of developer key pair

Creates (for developer keys):

• private.pem - Private key for signing
• public.pem - Public key for verification
• Displays the extension ID in console

Creates (for publisher keys):

• publisher-private.pem - Publisher private key for signing (ECDSA P-256)
• publisher-public.pem - Publisher public key for verification (ECDSA P-256)

get-crx-id

Get CRX ID (extension ID) from a public key.

crx3-pack get-crx-id -k <key>

Options:

• -k, --key <path> - Public key file path in PEM format (required)

CRX3 Format

The CRX3 format is the current Chrome extension packaging format that replaced CRX2. It uses:

• Magic Number: Cr24 (4 bytes)
• Version: 3 (4 bytes, little-endian)
• Header Length: Length of protobuf header (4 bytes, little-endian)
• Protobuf Header: Contains signatures and metadata
• ZIP Content: The actual extension files

The protobuf schema includes:

• RSA-SHA256 signatures with PKCS#1 PSS padding
• Public keys in X.509 SubjectPublicKeyInfo format
• CRX ID derived from the first 128 bits of the SHA-256 hash of the public key

Changelog

1.0.0

• Initial release
• Support for packing directories and zip files to CRX3
• CLI interface
• Key generation utilities
• TypeScript support