Diffie hellman algorithm

Question

        try{
                BigInteger p = new BigInteger(1, primeA);
                BigInteger g = new BigInteger("5");
                KeyPairGenerator keyGen = KeyPairGenerator.getInstance("DH");
                DHParameterSpec dhSpec = new DHParameterSpec(p, g, 1024 );
                keyGen.initialize(dhSpec);
                KeyPair keypair = keyGen.generateKeyPair();
                PrivateKey privateKey = keypair.getPrivate();
                PublicKey publicKey = keypair.getPublic();
                byte[] pub = publicKey.getEncoded();
                byte[] priv = privateKey.getEncoded();
                System.out.println("PRIVATE KEY=" + priv.length + "   PUBLIC KEY=" +pub.length);
                X509EncodedKeySpec x509KeySpec = new X509EncodedKeySpec(pub);
                KeyFactory keyFact = KeyFactory.getInstance("DH");
                publicKey = keyFact.generatePublic(x509KeySpec);
                KeyAgreement ka = KeyAgreement.getInstance("DH");
                ka.init(privateKey);
                ka.doPhase(publicKey, true);
                byte []secretKey = ka.generateSecret();
                 System.out.println("------------------------------------"  +secretKey.length);
                convertByte2Hex(secretKey , "  secretKey  " ) ;
        } catch (java.lang.NumberFormatException nfe) {System.out.println("iNumber format exception");
        } catch (java.security.InvalidAlgorithmParameterException e) {
        } catch (java.security.NoSuchAlgorithmException e) {
        }catch(Exception e) {e.printStackTrace();System.out.println("MAIN EXCEPTION ");}I have 2 problems here.
The public and the private key arrays that are generated are of length 298 and 296 (keeps changing) . I want to set the size of these values to be 128 bytes How can i Do that ?
Do we need to provide the value of vendor public key at
X509EncodedKeySpec x509KeySpec = new X509EncodedKeySpec(pub); !!!
Thanks
Sandesh

Answer 1

The public and the private key arrays that are generated are of length 298 and 296 (keeps changing) . I want to set the size of these values to be 128 bytes How can i Do that ?
I think, you can't. Using 1024 as "the size in bits of the random exponent (private value)" means that the encoding contains some additional bits of overhead plus the bits of p and g (or something like that). You'd have to use much shorted exponent in order to fit into 128 bytes. I wouldn't do it.
Do we need to provide the value of vendor public key at X509EncodedKeySpec x509KeySpec = new X509EncodedKeySpec(pub); !!!
Is it a question? I don't understand.
Btw., you should NEVER swallow exceptions.