AES 256 GCM | Authenticated Encryption and Decryption

aes256-gcm.mjs

import { randomBytes, createCipheriv, createDecipheriv } from 'node:crypto';

const aes256gcm = (key) => {

    const encrypt = (str) => {
        const iv = new randomBytes(12);
        const cipher = createCipheriv('aes-256-gcm', key, iv);

        let enc1 = cipher.update(str, 'utf8');
        let enc2 = cipher.final();

        return Buffer.concat([enc1, enc2, iv, cipher.getAuthTag()]).toString("base64");
    };

    const decrypt = (enc) => {
        enc = Buffer.from(enc, "base64");

        const iv = enc.slice(enc.length - 28, enc.length - 16);
        const tag = enc.slice(enc.length - 16);

        enc = enc.slice(0, enc.length - 28);

        const decipher = createDecipheriv('aes-256-gcm', key, iv);

        decipher.setAuthTag(tag);

        let str = decipher.update(enc, null, 'utf8');

        str += decipher.final('utf8');

        return str;
    };

    return {
        encrypt,
        decrypt,
    };
};

// Must be 32 bytes.
const SECRET = '12345678901234567890123456789012';

const cipher = aes256gcm(SECRET);

const plaintext = 'Hello World!'

const encrypted = cipher.encrypt(plaintext);
const decrypted = cipher.decrypt(encrypted);

console.log({ encrypted, decrypted });