JavaScript AES 256 CBC mixin (pure JavaScript encryption and decryption, stored base64 encoded)

crypt.js

import aesjs from 'aes-js'
import sha256 from 'js-sha256'

/**
 * Encryption Mixin (AES-CBC-256)
 */
export default {
    name: 'crypt',
    methods: {
        /**
         * Decrypts a AES CBC encrypted and base64 decoded password with the passphrase
         *
         * @param encrypted {string}
         * @param passphrase {string}
         * @returns {string}
         */
        decrypt(encrypted, passphrase) {
            // Blocksize = 32, IV size = 16
            let hash = sha256.create();

            // We need the digest
            let key = hash.update(passphrase).digest();

            encrypted = new Buffer(encrypted, 'base64');

            let iv = encrypted.slice(0, 16);
            let aesCbc = new aesjs.ModeOfOperation.cbc(key, iv);
            let decryptedBytes = aesCbc.decrypt(encrypted.slice(16));

            let last = decryptedBytes[decryptedBytes.length - 1];

            return aesjs.utils.utf8.fromBytes(decryptedBytes.slice(0, -last));
        },

        /**
         * Encrypt the given string with AES CBC 256 bit and the passphrase and base64 (for storing) encodes it
         * @param clearText {string}
         * @param passphrase {string}
         * @returns {string}
         */
        encrypt: function (clearText, passphrase) {
            let bs = 32;
            let hash = sha256.create();

            this.passphrase = 'secure';

            // We need the digest
            let key = hash.update(passphrase).digest();

            let clearBytes = aesjs.utils.utf8.toBytes(clearText);

            // We need a min length
            let fillCount = (bs - clearBytes.length % bs);
            let char = String.fromCharCode(fillCount);

            // Pad it to up
            for (let i = 0; i < fillCount; i++) {
                clearText += char;
            }

            clearBytes = aesjs.utils.utf8.toBytes(clearText);

            let crypto = window.crypto || window.msCrypto; // for IE 11
            let iv = new Uint8Array(16);

            // Get a set of random numbers (0-255)
            crypto.getRandomValues(iv);

            let aesCbc = new aesjs.ModeOfOperation.cbc(key, iv);
            let cryptedBytes = aesCbc.encrypt(clearBytes);

            // Add the IV in the beginning (our salt)
            let withIv = new Uint8Array(iv.length + cryptedBytes.length);
            withIv.set(iv);
            withIv.set(cryptedBytes, iv.length);

            return new Buffer(withIv).toString('base64');
        }
    }
}