JSEncrypt

A tiny (18.5kB gzip), zero dependency, JavaScript library to perform both synchronous and asynchronous OpenSSL RSA Encryption, Decryption, and Key Generation in both the Browser and Node.js.

🌐 Documentation: https://travistidwell.com/jsencrypt
📦 NPM Package: https://www.npmjs.com/package/jsencrypt
🚀 Interactive Demo: https://travistidwell.com/jsencrypt/demo

Why JSEncrypt?

When choosing an RSA encryption library for JavaScript, you need a solution that's reliable, secure, and fits seamlessly into your development workflow. JSEncrypt delivers on all fronts.

JSEncrypt stands out by providing enterprise-grade RSA encryption capabilities without the complexity and security concerns that come with heavy dependencies.

Key Benefits

• ⚡ Tiny & Fast - Just 18.5 kB gzipped - minimal impact on your bundle size.
• 🌐 Universal Compatibility - Works seamlessly in both Node.js server environments and browser applications
• 📦 Zero Dependencies - No external dependencies means better security posture and reduced bundle size
• ⚡ Flexible Execution - Supports both synchronous and asynchronous JavaScript patterns
• 🔒 OpenSSL Compatible - Direct support for PEM-formatted keys generated with OpenSSL
• 🛡️ Proven Security - Built on Tom Wu's battle-tested jsbn library without modifying core algorithms
• 🚀 Production Ready - Lightweight, well-tested, and used by thousands of developers worldwide

Installation

Using npm

npm install jsencrypt

Using yarn

yarn add jsencrypt

Using CDN

Include JSEncrypt directly in your HTML:

<script src="https://cdn.jsdelivr.net/npm/jsencrypt@latest/bin/jsencrypt.min.js"></script>

Basic Usage

1. Import the Library

ES6 Modules

import { JSEncrypt } from 'jsencrypt';

CommonJS

const JSEncrypt = require('jsencrypt');

Browser Global

// JSEncrypt is available globally when using CDN
const crypt = new JSEncrypt();

2. Create RSA Keys

For the highest security, you'll need RSA key pairs to use JSEncrypt. Generate them using OpenSSL:

# Generate a 2048-bit private key
openssl genrsa -out private.pem 2048

# Extract the public key
openssl rsa -pubout -in private.pem -out public.pem

3. Basic Encryption/Decryption

// Create JSEncrypt instance
const crypt = new JSEncrypt();

// Set your private key (for decryption)
crypt.setPrivateKey(`-----BEGIN RSA PRIVATE KEY-----
MIIEowIBAAKCAQEA4f5wg5l2hKsTeNem/V41fGnJm6gOdrj8ym3rFkEjWT9u
U38KPhX7l3YXkLMfJj8sE3PUi0EaL6rN6rOUY8dq1fQhPhT1wfI6V8KQtQnq
1FKnNgQCVmQpCxK7qFR7Z+9MRWoJrPb8lZMmT1ELkKL6FBfkp3H3WcTl+BF0
XoZnLK0CfXfKzPJPm9jfKKE7dqnCsRiXYJbBwkNpQ5xo2lRKnNaH8GjPzJ4X
TZ5J7G6hDpXN1F3YzWZNVQRzfDfLB+w9FDaZ5kFhRc2PgB1Y8dNOhgK7RFJF
JDZhqBhSRnQ1YkLkQOnHq4Bz8l7YgRJkJHdIfTOO8l3YXkLMfJj8sE3PUi0E
qL6r9OOCzGJnVgQCVmQpCxK7qFR7Z+9MRWoJrPb8lZMmT1ELkKL6FBfkp3H3
...
-----END RSA PRIVATE KEY-----`);

// The public key is automatically derived from the private key
// Or you can set it explicitly:
// crypt.setPublicKey('-----BEGIN PUBLIC KEY-----...');

// Encrypt data
const originalText = 'Hello, World!';
const encrypted = crypt.encrypt(originalText);

// Decrypt data
const decrypted = crypt.decrypt(encrypted);

console.log('Original:', originalText);
console.log('Encrypted:', encrypted);
console.log('Decrypted:', decrypted);
console.log('Match:', originalText === decrypted); // true

Key Concepts

Public vs Private Keys

• Public Key: Used for encryption. Safe to share publicly.
• Private Key: Used for decryption. Keep this secret!

const crypt = new JSEncrypt();

// For encryption only (using public key)
crypt.setPublicKey(publicKeyString);
const encrypted = crypt.encrypt('secret message');

// For decryption (requires private key)
crypt.setPrivateKey(privateKeyString);  
const decrypted = crypt.decrypt(encrypted);

Key Generation

JSEncrypt supports two approaches for obtaining RSA keys: OpenSSL generation (recommended) and JavaScript generation (convenient but less secure).

Option 1: OpenSSL Key Generation (Recommended)

For production applications and maximum security, generate keys using OpenSSL:

# Generate a 2048-bit private key (recommended minimum)
openssl genrsa -out private.pem 2048

# Generate a 4096-bit private key (higher security)
openssl genrsa -out private.pem 4096

# Extract the public key
openssl rsa -pubout -in private.pem -out public.pem

# View the private key
cat private.pem

# View the public key  
cat public.pem

Why OpenSSL is more secure:

• Uses cryptographically secure random number generators
• Better entropy sources from the operating system
• Optimized and audited implementations
• Industry standard for key generation

Option 2: JavaScript Key Generation (Convenience)

JSEncrypt can generate keys directly in JavaScript, which is convenient for testing, demos, or non-critical applications:

// Create JSEncrypt instance
const crypt = new JSEncrypt();

// Generate a new key pair (default: 1024-bit)
const privateKey = crypt.getPrivateKey();
const publicKey = crypt.getPublicKey();

console.log('Private Key:', privateKey);
console.log('Public Key:', publicKey);

// You can also specify key size (512, 1024, 2048, 4096)
const crypt2048 = new JSEncrypt({ default_key_size: 2048 });
const strongerPrivateKey = crypt2048.getPrivateKey();
const strongerPublicKey = crypt2048.getPublicKey();

Asynchronous Key Generation

For better performance (especially with larger keys), use async generation:

// Asynchronous key generation (recommended for larger keys)
const crypt = new JSEncrypt({ default_key_size: 2048 });

crypt.getKey(() => {
    const privateKey = crypt.getPrivateKey();
    const publicKey = crypt.getPublicKey();
    
    console.log('Generated private key:', privateKey);
    console.log('Generated public key:', publicKey);
    
    // Now you can use the keys
    const encrypted = crypt.encrypt('Hello, World!');
    const decrypted = crypt.decrypt(encrypted);
});

Different Key Sizes

// 512-bit (fast but less secure - only for testing)
const crypt512 = new JSEncrypt({ default_key_size: 512 });

// 1024-bit (default - basic security)
const crypt1024 = new JSEncrypt({ default_key_size: 1024 });

// 2048-bit (recommended minimum for production)
const crypt2048 = new JSEncrypt({ default_key_size: 2048 });

// 4096-bit (high security but slower)
const crypt4096 = new JSEncrypt({ default_key_size: 4096 });

⚠️ Security Note: JavaScript key generation uses browser/Node.js random number generators which may have less entropy than dedicated cryptographic tools. For production applications handling sensitive data, prefer OpenSSL-generated keys.

💡 Use Cases for JavaScript Generation:

• Rapid prototyping and testing
• Client-side demos and examples
• Educational purposes
• Non-critical applications
• When OpenSSL is not available

Advanced Features

Digital Signatures

// Sign with the private key
const sign = new JSEncrypt();
sign.setPrivateKey(privateKey);
const signature = sign.signSha256(data);

// Verify with the public key
const verify = new JSEncrypt();
verify.setPublicKey(publicKey);
const verified = verify.verifySha256(data, signature);

OAEP Padding

// Encrypt with OAEP padding and SHA-256 hash
const encrypt = new JSEncrypt();
encrypt.setPublicKey(publicKey);
const encrypted = encrypt.encryptOAEP(data);

Supported Hash Functions

When using signatures, you can specify the hash type:

• md2, md5, sha1, sha224, sha256, sha384, sha512, ripemd160

Browser Usage

For direct browser usage without a build system:

<!DOCTYPE html>
<html>
<head>
    <title>JSEncrypt Example</title>
    <script src="https://cdn.jsdelivr.net/npm/jsencrypt/bin/jsencrypt.min.js"></script>
</head>
<body>
    <script>
        const crypt = new JSEncrypt();
        crypt.setPrivateKey(crypt.getPrivateKey());
        
        // Use the library
        const encrypted = crypt.encrypt('Hello World!');
        const decrypted = crypt.decrypt(encrypted);
        
        console.log('Original:', 'Hello World!');
        console.log('Encrypted:', encrypted);
        console.log('Decrypted:', decrypted);
    </script>
</body>
</html>

Node.js Usage

For use within Node.js, you can use the following.

const JSEncrypt = require('jsencrypt');
const crypt = new JSEncrypt();
crypt.setPrivateKey(crypt.getPrivateKey());

// Use the library
const encrypted = crypt.encrypt('Hello World!');
const decrypted = crypt.decrypt(encrypted);

console.log('Original:', 'Hello World!');
console.log('Encrypted:', encrypted);
console.log('Decrypted:', decrypted);

Development & Testing

Running Tests

# Run all tests (Node.js + Browser)
npm test

# Run only Node.js tests  
npm run test:mocha

# Run only example validation tests
npm run test:examples

# Build the library
npm run build

# Build test bundle for browser testing
npm run build:test

Browser Tests

Visit the test page to run browser-based tests:

• Local development: http://localhost:4000/test/ (when running Jekyll)
• Online: https://travistidwell.com/jsencrypt/test/

Documentation

For comprehensive documentation, examples, and API reference:

📖 Visit the Documentation Site

• Getting Started Guide
• API Reference
• Examples & Use Cases
• Interactive Demo

Technical Background

This library provides a simple JavaScript wrapper around Tom Wu's excellent jsbn library. The core cryptographic functions remain untouched, ensuring security and reliability.

Key Format Support

JSEncrypt works with standard PEM-formatted RSA keys:

Private Key (PKCS#1):

-----BEGIN RSA PRIVATE KEY-----
MIICXgIBAAKBgQDHikastc8+I81zCg/qWW8dMr8mqvXQ3qbPAmu0RjxoZVI47tvs...
-----END RSA PRIVATE KEY-----

Public Key (PKCS#8):

-----BEGIN PUBLIC KEY-----
MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQDlOJu6TyygqxfWT7eLtGDwajtN...
-----END PUBLIC KEY-----

RSA Variable Mappings

The library translates PEM key components to jsbn library variables:

PEM Component	jsbn Variable
modulus	n
public exponent	e
private exponent	d
prime1	p
prime2	q
exponent1	dmp1
exponent2	dmq1
coefficient	coeff

Contributing

Contributions are welcome! Please read our contributing guidelines and ensure all tests pass before submitting a pull request.

# Clone the repository
git clone https://github.com/travist/jsencrypt.git
cd jsencrypt

# Install dependencies
npm install

# Run tests
npm test

# Build the project
npm run build

License

This project is licensed under the MIT License - see the LICENSE.txt file for details.

Resources

• Tom Wu's jsbn library: http://www-cs-students.stanford.edu/~tjw/jsbn/
• RSA Key Breakdown: http://etherhack.co.uk/asymmetric/docs/rsa_key_breakdown.html
• RSA Algorithm Details: http://www.di-mgt.com.au/rsa_alg.html
• ASN.1 Key Structures: https://polarssl.org/kb/cryptography/asn1-key-structures-in-der-and-pem

---

Made with ❤️ by Travis Tidwell