(Excel) AES 256-bit CBC using PBKDF2 Generated Secret Key

See more Encryption Examples

First generates a 32-byte secret key using PBKDF2 (with HMAC-SHA256), and then uses the secret key to do 256-bit AES CBC mode decryption.

(Duplicates the following Java code)

public String decrypt(String strToDecrypt) {
        try  {
            // Read the initialization vector from the first bytes for the data
            byte [] rawData = Base64.getDecoder().decode(strToDecrypt);
            byte [] iv = new byte[Config.get().encryptionIVLength()];
            byte [] encryptedData = new byte[rawData.length - iv.length];
            System.arraycopy(rawData, 0, iv, 0, iv.length);
            System.arraycopy(rawData, iv.length, encryptedData, 0, encryptedData.length);
 
            IvParameterSpec ivspec = new IvParameterSpec(iv);
 
            SecretKeyFactory factory = SecretKeyFactory.getInstance("PBKDF2WithHmacSHA256");
            KeySpec spec = new PBEKeySpec(secretKey.toCharArray(), salt.getBytes(), 65536, 256);
            SecretKey tmp = factory.generateSecret(spec);
            SecretKeySpec secretKey = new SecretKeySpec(tmp.getEncoded(), "AES");
 
            Cipher cipher = Cipher.getInstance("AES/CBC/PKCS5PADDING");
            cipher.init(Cipher.DECRYPT_MODE, secretKey, ivspec);
            return new String(cipher.doFinal(encryptedData));
        }
        catch (Exception e) {
            log.error("Could not decrypt the string.", e);
        }
        return null;
    }

Download Excel Class Modules Chilkat Excel Class Modules

' This example requires the Chilkat API to have been previously unlocked.
' See Global Unlock Sample for sample code.

Dim crypt As Chilkat.Crypt2
Set crypt = Chilkat.NewCrypt2


password = "some arbitrary length password"
' We have 8 bytes of salt encoded using hex.
' (The salt can be any number of bytes, in any desired encoding such as base64, hex, etc.)

saltHex = "0102030405060708"

' Generate the 256-bit (32-byte) AES secret key we'll use to decrypt.

iterationCount = 65536

outputKeyBitLen = 256

secretKeyHex = crypt.Pbkdf2(password,"utf-8","sha256",saltHex,iterationCount,outputKeyBitLen,"hex")

' Setup for 256-bit AES CBC decryption.
crypt.CryptAlgorithm = "aes"
crypt.KeyLength = 256
crypt.CipherMode = "cbc"
crypt.PaddingScheme = 0

' The IV for AES is 16 bytes.

iv = "000102030405060708090A0B0C0D0E0F"
crypt.SetEncodedIV iv,"hex"

' Set the secret key for 256-bit AES.
crypt.SetEncodedKey secretKeyHex,"hex"

' AES decrypt
' assume our string to decrypt is base64

strToDecrypt = "...."
crypt.EncodingMode = "base64"

decryptedStr = crypt.DecryptStringENC(strToDecrypt)

Debug.Print decryptedStr