Can RSA keys be used for both encryption and signing?

Yes, RSA key pairs can be used for both encryption/decryption and digital signing/verification. However, it's considered best practice to use separate key pairs for different purposes.

Python (using cryptography library):

from cryptography.hazmat.primitives.asymmetric import rsa
from cryptography.hazmat.primitives import serialization, hashes
from cryptography.hazmat.primitives.asymmetric import padding

def generate_rsa_keypair(key_size=2048):
    # Generate private key
    private_key = rsa.generate_private_key(
        public_exponent=65537,
        key_size=key_size
    )
    
    # Get public key
    public_key = private_key.public_key()
    
    # Serialize private key to PEM
    private_pem = private_key.private_bytes(
        encoding=serialization.Encoding.PEM,
        format=serialization.PrivateFormat.PKCS8,
        encryption_algorithm=serialization.NoEncryption()
    )
    
    # Serialize public key to PEM
    public_pem = public_key.public_bytes(
        encoding=serialization.Encoding.PEM,
        format=serialization.PublicFormat.SubjectPublicKeyInfo
    )
    
    return private_pem, public_pem

# Example usage
private_key, public_key = generate_rsa_keypair(2048)
print("Private Key:", private_key.decode()[:100] + "...")
print("Public Key:", public_key.decode()[:100] + "...")
            

Node.js (using node-forge):

const forge = require('node-forge');

function generateRSAKeyPair(keySize = 2048) {
    // Generate key pair
    const keypair = forge.pki.rsa.generateKeyPair({
        bits: keySize,
        e: 0x10001 // 65537
    });
    
    // Convert to PEM format
    const privateKeyPem = forge.pki.privateKeyToPem(keypair.privateKey);
    const publicKeyPem = forge.pki.publicKeyToPem(keypair.publicKey);
    
    return {
        privateKey: privateKeyPem,
        publicKey: publicKeyPem,
        keySize: keySize
    };
}

function encryptWithPublicKey(publicKeyPem, message) {
    const publicKey = forge.pki.publicKeyFromPem(publicKeyPem);
    const encrypted = publicKey.encrypt(message, 'RSA-OAEP');
    return forge.util.encode64(encrypted);
}

// Example usage
const keys = generateRSAKeyPair(2048);
console.log('Key pair generated successfully');
console.log('Private key length:', keys.privateKey.length);
console.log('Public key length:', keys.publicKey.length);