SSHTools, SFTP, Bouncy Castle, JCE, AES128 CBC and other acronyms. Help me put them together.

[Paul Policarp]

Hi. I'm trying to implement a windows SFTP server using SSHTools (j2ssh) and it has to use AES 128 CBC encryption. SSHTools supposedly has classes for all this and they are all configurable in one of the configuration XMLs.

Or were.

The documentation is hardly up to date and the classes no longer exist, so I tried to recreate them. This is what my AES class looked like:

 
package com.sshtools.j2ssh.transport.cipher;

import com.sshtools.j2ssh.transport.AlgorithmOperationException;
import com.sshtools.j2ssh.transport.cipher.SshCipher;

import java.security.InvalidAlgorithmParameterException;
import java.security.InvalidKeyException;
import java.security.Key;
import java.security.NoSuchAlgorithmException;
import java.security.Security;
import java.security.spec.InvalidKeySpecException;
import java.security.spec.KeySpec;

import javax.crypto.Cipher;
import javax.crypto.NoSuchPaddingException;
import javax.crypto.SecretKeyFactory;
import javax.crypto.spec.DESedeKeySpec;
import javax.crypto.spec.IvParameterSpec;
import javax.crypto.spec.SecretKeySpec;


public class AES128cbc extends SshCipher {
    /**  */
    protected static String algorithmName = "aes128-cbc";
    Cipher cipher;

    /**
     * Creates a new AES128cbc object.
     */
    public AES128cbc() {
    }

    /**
     *
     *
     * @return
     */
    public int getBlockSize() {
        return cipher.getBlockSize();
    }

    /**
     *
     *
     * @param mode
     * @param iv
     * @param keydata
     *
     * @throws AlgorithmOperationException
     */
    public void init(int mode, byte[] iv, byte[] keydata)
        throws AlgorithmOperationException {
        try {
            KeySpec keyspec;
            Key key;
            
            Security.addProvider(new org.bouncycastle.jce.provider.BouncyCastleProvider());

            // Create the cipher according to its algorithm
            cipher = Cipher.getInstance("AES/CBC/NoPadding");

            byte[] actualKey = new byte[24];
            System.arraycopy(keydata, 0, actualKey, 0, 24);
            keyspec = new SecretKeySpec(actualKey, "AES");
            key = SecretKeyFactory.getInstance("AES").generateSecret(keyspec);
            cipher.init(((mode == ENCRYPT_MODE) ? Cipher.ENCRYPT_MODE
                                                : Cipher.DECRYPT_MODE), key,
                new IvParameterSpec(iv, 0, cipher.getBlockSize()));
        } catch (NoSuchPaddingException nspe) {
            throw new AlgorithmOperationException("Padding not supported");
        } catch (NoSuchAlgorithmException nsae) {
            throw new AlgorithmOperationException("Algorithm not supported");
        } catch (InvalidKeyException ike) {
            throw new AlgorithmOperationException("Invalid encryption key");
        } catch (InvalidKeySpecException ispe) {
            throw new AlgorithmOperationException(
                "Invalid encryption key specification");
        } catch (InvalidAlgorithmParameterException ape) {
            throw new AlgorithmOperationException("Invalid algorithm parameter");
        }
    }

    /**
     *
     *
     * @param data
     * @param offset
     * @param len
     *
     * @return
     *
     * @throws AlgorithmOperationException
     */
    public byte[] transform(byte[] data, int offset, int len)
        throws AlgorithmOperationException {
        return cipher.update(data, offset, len);
    }
}
   

Basically I just copy-pasted their CBC DES class and replaced the essentials. I load it via the XML file but when I try to connect with a linux client and using the cipher, my server throws a socket is EOF IO exception after my client says it cannot find the AES cipher on the server, just the two that are part of the API.

So I edited the SSHTools API to make it load the AES class by default without needing the XML file.

public class SshCipherFactory {
    private static HashMap ciphers;
    private static String defaultCipher;
    private static Log log = LogFactory.getLog(SshCipherFactory.class);
    private static ArrayList supported;

    static {
        ciphers = new HashMap();

        log.info("Loading supported cipher algorithms");

        ciphers.put("3des-cbc", TripleDesCbc.class);
        ciphers.put("blowfish-cbc", BlowfishCbc.class);
        ciphers.put("aes128-cbc", AES128cbc.class);
        defaultCipher = "aes128-cbc";

...

Now whenever I try to connect, I don't get an exception, but rather the server hangs on

07.05.2010 16:27:05 com.sshtools.j2ssh.transport.cipher.SshCipherFactory newInstance
INFO: Creating new aes128-cbc cipher instance

Please help me with this. I've been working on this damned server for months now and I'm quite literally at wit's end. If you need any more information I will gladly supply it.

Thanks.

[Paul Policarp]

I've solved the problem, this thread can be closed.

[Paul Policarp]

Just in case anyone's interested, this is my cipher (and this is my gun).

package com.sshtools.j2ssh.transport.cipher;

import com.sshtools.j2ssh.transport.AlgorithmOperationException;

import java.security.InvalidAlgorithmParameterException;
import java.security.InvalidKeyException;
import java.security.Key;
import java.security.NoSuchAlgorithmException;
import java.security.NoSuchProviderException;
import java.security.Security;
import java.security.spec.InvalidKeySpecException;

import javax.crypto.Cipher;
import javax.crypto.KeyGenerator;
import javax.crypto.NoSuchPaddingException;
import javax.crypto.SecretKey;
import javax.crypto.SecretKeyFactory;
import javax.crypto.spec.IvParameterSpec;
import javax.crypto.spec.SecretKeySpec;


public class AES128cbc extends SshCipher {
    /**  */
    protected static String algorithmName = "aes128-cbc";
    Cipher cipher;

    /**
     * Creates a new AES128cbc object.
     */
    public AES128cbc() {
    }

    /**
     *
     *
     * @return
     */
    public int getBlockSize() {
        return cipher.getBlockSize();
    }

    /**
     *
     *
     * @param mode
     * @param iv
     * @param keydata
     *
     * @throws AlgorithmOperationException
     */
    public void init(int mode, byte[] iv, byte[] keydata)
        throws AlgorithmOperationException {
        try {
            SecretKeySpec keyspec;
            SecretKey key;
            
            //Security.addProvider(new org.bouncycastle.jce.provider.BouncyCastleProvider());

            // Create the cipher according to its algorithm
            //KeyGenerator kgen = KeyGenerator.getInstance("AES");
            //kgen.init(128); // 192 and 256 bits may not be available
            
            cipher = Cipher.getInstance("AES/CBC/NOPADDING");   
            
            byte[] actualKey = new byte[16];
            System.arraycopy(keydata, 0, actualKey, 0, 16);
            keyspec = new SecretKeySpec(actualKey, "AES");
            //key = kgen.generateKey();
            //key = SecretKeyFactory.getInstance("AES").generateSecret(keyspec);
            
            cipher.init(((mode == ENCRYPT_MODE) ? Cipher.ENCRYPT_MODE
                                                : Cipher.DECRYPT_MODE), keyspec,
                new IvParameterSpec(iv, 0, cipher.getBlockSize()));
        } catch (NoSuchPaddingException nspe) {
            throw new AlgorithmOperationException("Padding not supported");
        } catch (NoSuchAlgorithmException nsae) {
            throw new AlgorithmOperationException("Algorithm not supported");
        } catch (InvalidKeyException ike) {
            throw new AlgorithmOperationException("Invalid encryption key");
        } /*catch (InvalidKeySpecException ispe) {
            throw new AlgorithmOperationException(
                "Invalid encryption key specification");
        }*/ catch (InvalidAlgorithmParameterException ape) {
            throw new AlgorithmOperationException("Invalid algorithm parameter");
        } /*catch (NoSuchProviderException nspre) {
        	throw new AlgorithmOperationException("No Such Provider");
        }*/
    }

    /**
     *
     *
     * @param data
     * @param offset
     * @param len
     *
     * @return
     *
     * @throws AlgorithmOperationException
     */
    public byte[] transform(byte[] data, int offset, int len)
        throws AlgorithmOperationException {
        return cipher.update(data, offset, len);
    }
}
    

Notable changes include the usage of SecretKeySpec in cipher.init and the keysize of 16 bytes (128 bits). It's working now.