AES
- Node.js course
- Intermediate
- Lesson 104/116
- 5 min
Learn AES encryption with crypto.createCipheriv.
AES encryption
AES (Advanced Encryption Standard) is two-way symmetric encryption. The same key is used for both encryption and decryption. In Node.js you create a cipher with crypto.createCipheriv(algorithm, key, iv).
Example: const cipher = crypto.createCipheriv("aes-256-cbc", key, iv);. Here key must be 32 bytes (256 bits), iv 16 bytes (initialization vector). The iv must differ for each encryption; you generate it with crypto.randomBytes(16). Encryption: cipher.update("text", "utf8", "hex") and cipher.final("hex"). Decryption: crypto.createDecipheriv uses the same key and iv. In AES-CBC mode the ciphertext is a multiple of the block size (16 bytes); PKCS7 padding is applied. The key and iv must be stored or transmitted together safely.
Key and IV
For AES-256-CBC the key must be 32 bytes, the IV 16 bytes. The IV must be unique for each encryption; with the same key and IV the same plaintext gives the same ciphertext. This opens the door to replay attacks.
Example: const key = crypto.randomBytes(32); const iv = crypto.randomBytes(16);. The key is stored long-term in a safe place. The IV is regenerated for each encryption and sent alongside the ciphertext (it need not stay secret). To decrypt, the same IV is needed: crypto.createDecipheriv("aes-256-cbc", key, iv). The key must be a Buffer; randomBytes already returns one. With the wrong key or IV decryption throws.
Practice Encrypt text with AES
Import with const crypto = require("node:crypto");. Generate key and IV with const key = crypto.randomBytes(32); and const iv = crypto.randomBytes(16);. Create cipher with const cipher = crypto.createCipheriv("aes-256-cbc", key, iv);. Encrypt with let enc = cipher.update("gizli", "utf8", "hex"); enc += cipher.final("hex");. Print with console.log("Ciphertext length: " + enc.length).
Starter code
// Import the crypto module
// write here
// Generate key and IV
// write here
// Create cipher
// write here
// Encrypt "gizli"
// write here
// Print "Ciphertext length: ..."
// write hereSample solution
const crypto = require("node:crypto");
const key = crypto.randomBytes(32);
const iv = crypto.randomBytes(16);
const cipher = crypto.createCipheriv("aes-256-cbc", key, iv);
let enc = cipher.update("gizli", "utf8", "hex");
enc += cipher.final("hex");
console.log("Ciphertext length: " + enc.length);Expected output
Şifreli uzunluk: 32
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 Complete the createCipheriv call
const cipher = crypto.____("aes-256-cbc", key, iv);const cipher = crypto.createCipheriv("aes-256-cbc", key, iv);Explanation: createCipheriv creates an AES cipher.
2 Which three parameters does createCipheriv take?
crypto.createCipheriv(alg, key, iv)- algoritma, metin, anahtar
- algoritma, anahtar, IV Correct answer
- algoritma, IV, metin
- anahtar, IV, metin
Explanation: It takes algorithm, key, and IV.
3 Match each piece to its role
| Term | Meaning |
|---|---|
createCipheriv |
Creates cipher |
key |
32-byte key |
iv |
16-byte init vector |
update/final |
Produces ciphertext |