Help loading Diffie-Hellman keys from file

[Scott Barnhart]

Hi,

I am trying to use CryptoPP 5.1 to decode files encoded with the Java crypto classes 
using Diffie-Hellman keys and DESede encryption (CBC mode, PKCS5 padding).  The 
problem I can not figure out at this point is how to load a 1024-bit Diffie-Hellman 
public or private key from a file, where the public key is in X509 format, and the 
private key is PKCS#8 format.  The DH::Agree() method wants byte* arguments for the 
keys, in (I assume) an un-encoded format.  I am getting totally lost in how to use all 
the different template classes and arguments to template classes to construct what I 
want.  All the DH sample code shows generating keys, and then using those same keys 
immediately to do the DH agreement.  But I can't find any code which shows how to load 
DH keys from a file system.

Can someone please show me some code or some pointers in the right direction on how to 
do this?  I have used CryptoPP for some other stuff (DefaultEncryptorWithMAC), and I 
understand Sources, Sinks, and Transformations pretty well, but I can NOT figure this 
out.  Any help would be greatly appreciated.

Here is the Java code I use to generate and save the DH keys:

    DHParameterSpec dhSkipParamSpec = new DHParameterSpec(skip1024Modulus, 
skip1024Base);
    KeyPairGenerator keyPairGen = KeyPairGenerator.getInstance("DH");
    keyPairGen.initialize(dhSkipParamSpec);
    KeyPair keyPair = keyPairGen.generateKeyPair();

    writeKey(keyPair.getPublic(),  "Public.bin");
    writeKey(keyPair.getPrivate(), "Private.bin");

    private void writeKey(Key key, String strName) throws Exception 
    {
        FileOutputStream fKey = new FileOutputStream(strName);
        fKey.write(key.getEncoded());   // java getEncoded() returns X509 format for 
public key, PKCS#8 for private
        fKey.close();
    }


The java code to encode looks like:

    private void run(String strPriFile, String strPubFile, String strFileToEncode) 
throws Exception 
    {
        KeyFactory facDH = KeyFactory.getInstance("DH");
        KeySpec pubKeySpec = new X509EncodedKeySpec(getRawKey(strPubFile));
        KeySpec priKeySpec = new PKCS8EncodedKeySpec(getRawKey(strPriFile));

        PublicKey pubKey  = facDH.generatePublic(pubKeySpec);
        PrivateKey priKey = facDH.generatePrivate(priKeySpec);

        KeyAgreement keyAgree = KeyAgreement.getInstance("DH");
        keyAgree.init(priKey);
        keyAgree.doPhase(pubKey, true);
        SecretKey keySecret = keyAgree.generateSecret("DESede");     // Transforms the 
DH agreed secret value into a 168-bit 3DES key.

        Cipher cipher = Cipher.getInstance("DESede/CBC/PKCS5Padding");
        cipher.init(Cipher.ENCRYPT_MODE, keySecret);

        FileInputStream  fIn  = new FileInputStream(strFileToEncode);
        DataOutputStream fOut = new DataOutputStream(new 
FileOutputStream(strFileToEncode + ".enc"));

        byte[] iv = cipher.getIV(); // get the initialization vector
        fOut.write(iv); // write IV

        // Read from the input and write to the encrypting output stream
        byte[] buffer = new byte[BUFSIZE];
        int bytesRead;
        while((bytesRead = fIn.read(buffer)) != -1) 
        {
            fOut.write(cipher.update(buffer, 0, bytesRead));
        }
        fOut.write(cipher.doFinal());
        fOut.close();
        fIn.close();
    }

    private byte[] getRawKey(String strFile) throws Exception
    {
        File keyfile = new File(strFile);
        DataInputStream in = new DataInputStream(new FileInputStream(keyfile));
        byte[] rawkey = new byte[(int)keyfile.length()];
        in.readFully(rawkey);
        in.close();
        return rawkey;
    }

Thanks,
Scott Barnhart
[EMAIL PROTECTED]