On Java, OpenSSL, Crypto, Blowfish and stuff

During some Android malware analysis I came along some Java routines which were meant to decrypt/encrypt some content. Nothing special about it. The key had to be extracted from a file and the encrypted file was in Base64. After unsuccessfully trying openssl in order to decrypt the file I decided to make some further investigations.

In this article I'll have a look how Python, Java and openssl (command line utility) implement Blowfish in CBC mode. Furthermore I want to know if data encrypted with Python can be later on decrypted with Java and viceversa. Following compatibility dependencies might be interesting:

  1. Python <-> Java
  2. Java <-> openssl
  3. Python <-> openssl

Java

Let's take a look at some routines in Java. You can also view/download the following code on this GitHub Gist.

/*
 * Based on https://raw.githubusercontent.com/usefulfor/usefulfor/master/security/JBoss.java
 *
 * JBoss.java - Blowfish encryption/decryption tool with JBoss default password
 *    Daniel Martin Gomez <[email protected]> - 03/Sep/2009
 *
 * This file may be used under the terms of the GNU General Public License
 * version 2.0 as published by the Free Software Foundation:
 *   http://www.gnu.org/licenses/gpl-2.0.html
 */
import javax.crypto.*;
import javax.crypto.spec.SecretKeySpec;

import java.math.BigInteger;
import javax.xml.bind.DatatypeConverter;

public class JBlowfish
{
    final protected static char[] hexArray = "0123456789ABCDEF".toCharArray();

    // Converts byte array to hex string
    // From: http://stackoverflow.com/questions/9655181/convert-from-byte-array-to-hex-string-in-java
    public static String bytesToHex(byte[] bytes) {
        char[] hexChars = new char[bytes.length * 2];
        for ( int j = 0; j < bytes.length; j++ ) {
            int v = bytes[j] & 0xFF;
            hexChars[j * 2] = hexArray[v >>> 4];
            hexChars[j * 2 + 1] = hexArray[v & 0x0F];
        }
        return new String(hexChars);
    }

    public static void main(String[] args) throws Exception
    {

        if ( ( args.length != 2 ) || !( args[0].equals("-e") | args[0].equals("-d") ) )
        {
            System.out.println( "Usage:\n\tjava JBlowfish <-e|-d> <encrypted_password>" );
            return;
        }

        String mode = args[0];

        // Configuration
        byte[] key  = "secret".getBytes();
        String IV   = "12345678";


        System.out.println("-- Settings -----------");
        System.out.println("KEY:\t " + bytesToHex(key));
        System.out.println("IV:\t " + bytesToHex(IV.getBytes()));

        // Create new Blowfish cipher
        SecretKeySpec keySpec = new SecretKeySpec(key, "Blowfish");
        Cipher cipher = Cipher.getInstance("Blowfish/CBC/PKCS5Padding");
        String out = null;

        if ( mode.equals("-e") )
        {
            String secret = args[1];
            cipher.init(Cipher.ENCRYPT_MODE, keySpec, new javax.crypto.spec.IvParameterSpec(IV.getBytes()));
            byte[] encoding = cipher.doFinal(secret.getBytes());

            System.out.println("-- Encrypted -----------");
            System.out.println("Base64:\t " + DatatypeConverter.printBase64Binary(encoding));
            System.out.println("HEX:\t " + bytesToHex(encoding));
        }
        else
        {
            // Decode Base64
            byte[] ciphertext = DatatypeConverter.parseBase64Binary(args[1]);

            // Decrypt
            cipher.init(Cipher.DECRYPT_MODE, keySpec, new javax.crypto.spec.IvParameterSpec(IV.getBytes()));
            byte[] message = cipher.doFinal(ciphertext);

            System.out.println("-- Decrypted -----------");
            System.out.println("HEX:\t " + bytesToHex(message));
            System.out.println("PLAIN:\t " + new String(message));

        }
    }
}

The programm will encrypt messages using Blowfish in CBC mode. There are 2 modi available:

  • -e <message>: will encrypt the message < message >
  • -d <Base64>: will decrypt the specified Base64 string < Base64 >

The encryption key and the IV (initialization vector) are static. Let's see an example:

# javac JBlowfish.java
# java -cp . JBlowfish -e secretmessage
-- Settings -----------
KEY:     736563726574
IV:      3132333435363738
-- Encrypted -----------
Base64:  2CEndW0AA2xpsYz3XrXnrA==
HEX:     D82127756D00036C69B18CF75EB5E7AC

We just encrypted the message "secretmessage" with Blowfish/CBC. In the settings section you'll see the KEY and the IV in their hex representation. Afterwards the programm will show the Base64 and the hex representation of encrypted message. Decryption works quite straightforward:

# java -cp . JBlowfish -d 2CEndW0AA2xpsYz3XrXnrA==
-- Settings -----------
KEY:     736563726574
IV:      3132333435363738
-- Decrypted -----------
HEX:     7365637265746D657373616765
PLAIN:   secretmessage

Our little Java application does its job pretty fine. Ok, now let's have a look at openssl.

OpenSSL <-> Java

Using openssl I'll encrypt/decrypt the previous secret message with the same cipher:

# echo "secretmessage" | openssl bf-cbc -nosalt -a -pass pass:victor -iv 3132333435363738 -p
key=FFC150A160D37E92012C196B6AF4160D
iv =3132333435363738
+NtBjHQzii7i//apIvfHkw==

A few explanations:

  • bf-cbc: this is Blowfish with CBC
  • nosalt: Use no salt (which in general is very bad!)
  • -a: This means that if encryption is taking place the data is base64 encoded after encryption. If decryption is set then the input data is base64 decoded before being decrypted.
  • -pass: Specify the passphrase to encrypt the message with. This is actually not the encryption key openssl will use. The encryption key will be derived from the passphrase.
  • -iv: Specify IV in hex representation. In the Java code I've used IV="12345678 and hex(IV)=3132333435363738

As you can see the output of openssl looks quite different. Following observations:

Tool KEY IV Encrypted message (Base64)
Java 736563726574 3132333435363738 2CEndW0AA2xpsYz3XrXnrA==
openssl FFC150A160D37E92012C196B6AF4160D 3132333435363738 +NtBjHQzii7i//apIvfHkw==

Besides the IV everything looks different :(

Python <-> Java

Let's also have a look at Python:

In [67]:    from Crypto.Cipher import Blowfish
            from Crypto import Random
            from struct import pack
            from binascii import hexlify, unhexlify


            IV = "12345678"
            KEY = "secret"

            # We'll use the Base64 string from JBlowfish output
            ciphertext = "2CEndW0AA2xpsYz3XrXnrA==".decode("base64")

            cipher = Blowfish.new(KEY, Blowfish.MODE_CBC, IV)
            message = cipher.decrypt(ciphertext)
            print("KEY: " + KEY.encode("hex"))
            print("IV: " + IV.encode("hex"))
            print("Message: " + message)

Out:        KEY: 736563726574
            IV: 3132333435363738
            Message: secretmessage

Well that looks good. This is what we got:

Tool KEY IV
Java 736563726574 3132333435363738
python 736563726574 3132333435363738

Python <-> openssl

This time let's encrypt some message using Python:

In [71]:    from Crypto.Cipher import Blowfish
            from Crypto import Random
            from struct import pack
            from binascii import hexlify, unhexlify


            IV = "12345678"
            KEY = "secret"
            message = "12345678"


            cipher = Blowfish.new(KEY, Blowfish.MODE_CBC, IV)
            ciphertext = cipher.encrypt(message)
            print("HEX: " + ciphertext.encode("hex"))
            print("Base64: " + ciphertext.encode("base64"))

Out:        HEX: 010a0d9149750a32
            Base64: AQoNkUl1CjI=

Now decrypt that ciphertext using openssl:

# echo "AQoNkUl1CjI=" | openssl bf-cbc -d -a -nosalt -pass pass:secret -iv 3132333435363738  -p
key=5EBE2294ECD0E0F08EAB7690D2A6EE69
iv =3132333435363738
bad decrypt
140568446580392:error:06065064:digital envelope routines:EVP_DecryptFinal_ex:bad decrypt:evp_enc.c:539:

Again the encryption key doesn't match the one we used in the Python code. Thus the Bas64 string can't be decoded by openssl.

Conclusion

Obviously I'm not the only one facing this problem.

Not-Yet-Commons-SSL has an implementation of PBE ("password based encryption") that is 100% compatible with OpenSSL's command-line "enc" utility

That sounds promising but you should be warned:

Warning: All versions of not-yet-commons-ssl should be considered to be of "Alpha" quality! This code probably contains bugs. This code may have security issues.

as stated here.

If you still want some compatibility between openssl and your code, you should use the key and IV from openssl. Example:

# echo "this-is-secret" | openssl bf-cbc -a -nosalt -pass pass:secret -iv 12345678 -p
key=5EBE2294ECD0E0F08EAB7690D2A6EE69
iv =1234567800000000
2whDyIn5hRdyXpRZbMZayw==

Now use those values in your code:

In [72]:    from Crypto.Cipher import Blowfish
            from Crypto import Random
            from struct import pack
            from binascii import hexlify, unhexlify


            KEY = unhexlify("5EBE2294ECD0E0F08EAB7690D2A6EE69")
            IV = unhexlify("1234567800000000")
            ciphertext = "2whDyIn5hRdyXpRZbMZayw==".decode("base64")


            cipher = Blowfish.new(KEY, Blowfish.MODE_CBC, IV)
            ciphertext = cipher.decrypt(ciphertext)

            print("Message: " + message)

Out:        Message: 12345678

Also have a look at this. That's all for today. Cya next time!


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Published:
2014-07-01 00:00
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