我如何将生成的 AES 密钥从 Diffie-Hellman 类添加到我使用密钥的类中

Question

Background: I have two devices which communicate via IP/port connection establishing live voice encrypting communication thanks to Diffie-Hellman key-exchange and encrypting it thanks to AES algorithm. Now some of the code is written and some just taken to use as an example of the prototype implementation.

Problem: Now even when understanding how my classes work just like the title states: I can not figure out how to take the key from DH class and declare in AES class that this is the key it must use to encrypt.

Ps Advice on code optimization, better practices and general tips are most welcome, please. Thank you for your time.

public class DH extends Thread {

int bitLength=512;  
int certainty=20;//

private static final SecureRandom rnd = new SecureRandom();

public DH() throws Exception{
    Random randomGenerator = new Random();
    BigInteger generatorValue,primeValue,publicA,publicB,secretA,secretB,sharedKeyA,sharedKeyB;

    primeValue = findPrime();// BigInteger.valueOf((long)g);
    System.out.println("the prime is "+primeValue);
     generatorValue = findPrimeRoot(primeValue);//BigInteger.valueOf((long)p);
    System.out.println("the generator of the prime is "+generatorValue);

    // on machine 1
    secretA = new BigInteger(bitLength-2,randomGenerator);
    // on machine 2
    secretB = new BigInteger(bitLength-2,randomGenerator);

    // to be published:
    publicA=generatorValue.modPow(secretA, primeValue);
    publicB=generatorValue.modPow(secretB, primeValue);
    sharedKeyA = publicB.modPow(secretA,primeValue);// should always be same as:
    sharedKeyB = publicA.modPow(secretB,primeValue);

    String getAValue=sharedKeyA.toString();

    MessageDigest md = MessageDigest.getInstance("SHA-256");
    md.update(getAValue.getBytes());

    byte byteData[] = md.digest();
    StringBuffer sb = new StringBuffer();

    for(int i=0;i<byteData.length;i++)
    {
        sb.append(Integer.toString((byteData[i] & 0xff) + 0x100, 16).substring(1));// ??
    }

    String getHexValue = sb.toString();
    System.out.println("hex format in SHA-256 is "+getHexValue);

    byte [] initkey = getAValue.getBytes("UTF-8");

    MessageDigest sha = MessageDigest.getInstance("SHA-256");
    initkey =  sha.digest(initkey);
    initkey = Arrays.copyOf(initkey, 16);

    SecretKeySpec secretKeySpec =  new SecretKeySpec(initkey,"AES");

    Cipher cipher = Cipher.getInstance("AES");
    cipher.init(Cipher.ENCRYPT_MODE, secretKeySpec);



}

As you can see i have coded AES key and IV statically but want for the generated AES key in DH to be assigned in this class

public class AES {

static String IV = "AAAAAAAAAAAAAAAA";
static String initkey = "13B_0(wcXNGkHAR[";

public static byte[] encrypt(byte[] plainData, int offset, int length) throws Exception {


    Cipher cipher = Cipher.getInstance("AES/CBC/NoPadding");//CBC
    SecretKeySpec key = new SecretKeySpec(initkey.getBytes("UTF-8"), "AES");

    cipher.init(Cipher.ENCRYPT_MODE, key, new IvParameterSpec(IV.getBytes("UTF-8")));
    return cipher.doFinal(plainData, offset, length);
}

public static byte[] decrypt(byte[] cipherSound, int offset, int length) throws Exception {

    Cipher cipher = Cipher.getInstance("AES/CBC/NoPadding");//CBC
    SecretKeySpec key = new SecretKeySpec(initkey.getBytes("UTF-8"), "AES");

    cipher.init(Cipher.DECRYPT_MODE, key, new IvParameterSpec(IV.getBytes("UTF-8")));
    return cipher.doFinal(cipherSound, offset, length);
}

}

Answer 1

figure out how to take the key from DH class and declare in AES class that this is the key it must use to encrypt

Please check this tutorial

Then you can use the returned secret:

byte[] masterKey = aKeyAgree.generateSecret();
// maybe hash the master key too
SecretKeySpec key = new SecretKeySpec(masterKey, 0, 16, "AES");

However, if you have two way communication, you either need random IV or different keys for each direction (derived from the master)

Additional hint :

I have two devices which communicate via IP/port connection establishing live voice encrypting communication

Maybe your devices are powerful enough to establish proper TLS, what would solve many things for you