使用 AES/CFB/NoPadding、AES/OFB/NoPadding 或 AES/CBC/NoPadding 的密码太短

Question

Can someone help me reinforce or improve the following code to make the resulting passwords "longer".

I am humbly looking for the best way to use AES/CFB/NoPadding , or with AES/CBC/NoPadding , or with AES/OFB/NoPadding . We have tested with AES/GCM/NOPADDING . Which works with Java 8, but not with Java 7. And we need something that works in Java 7

For example, using ' safe ' as <key_to_encrypt>, and ' Bk206V4ytQ1zZAukPE6/2c5KUcxGYpBf ' as <encryption_key>, the pwd is: FX5O5A== which is quite bite "small"

import java.security.MessageDigest;

import javax.crypto.Cipher;
import javax.crypto.spec.IvParameterSpec;
import javax.crypto.spec.SecretKeySpec;

import org.apache.xml.security.utils.Base64;

public class StringEncrypt {

    private final static String ALG = "AES";
    private final static String CI = "AES/CFB/NoPadding";

    public static String encrypt(String cleartext, String key) throws Exception {   
        MessageDigest md = MessageDigest.getInstance("MD5");
        md.update(key.getBytes());
        IvParameterSpec iv = new IvParameterSpec(md.digest());
        
        Cipher cipher = Cipher.getInstance(CI);
        SecretKeySpec skeySpec = new SecretKeySpec(key.getBytes(), ALG);
        cipher.init(Cipher.ENCRYPT_MODE, skeySpec, iv);
        byte[] encrypted = cipher.doFinal(cleartext.getBytes());
        
        return new String(Base64.encode(encrypted));
    }

    public static String decrypt(String encrypted, String key) throws Exception {
        MessageDigest md = MessageDigest.getInstance("MD5");
        md.update(key.getBytes());
        IvParameterSpec iv = new IvParameterSpec(md.digest());

        Cipher cipher = Cipher.getInstance(CI);
        SecretKeySpec skeySpec = new SecretKeySpec(key.getBytes(), ALG);
        byte[] enc = Base64.decode(encrypted);
        cipher.init(Cipher.DECRYPT_MODE, skeySpec, iv);
        byte[] decrypted = cipher.doFinal(enc);
        
        return new String(decrypted);
    }

    public static void main(String[] args) throws Exception {
        if (args.length == 2) {
            String pwd = StringEncrypt.encrypt(args[0], args[1]);
            System.out.println("Key encryption: " + pwd);
            pwd = StringEncrypt.decrypt(pwd, args[1]);
            if (args[0].equals(pwd)) {
                System.out.println("[OK] Correct decryption!");
            } else {
                System.out.println("[KO] Wrong decryption!");
            }
        } else {
            System.out.println("The parameters are required: <key_to_encrypt> <encryption_key>");
        }
    }

}

Stated differently, could someone give me an example of good encryption / decryption that works in Java 7?

Answer 1

If you want to increase the length, you need to increase the byte count of the encrypted / decrypted parameter. You could hack this by changing the charset although I don't think is best practice:

        byte[] encrypted = cipher.doFinal(cleartext.getBytes(StandardCharsets.UTF_16));

        return new String(decrypted, StandardCharsets.UTF_16);