static byte[] buildDSA(DSAPublicKey key) {
DataByteOutputStream out = new DataByteOutputStream();
BigInteger q = key.getParams().getQ();
BigInteger p = key.getParams().getP();
BigInteger g = key.getParams().getG();
BigInteger y = key.getY();
int t = (p.toByteArray().length - 64) / 8;
out.writeByte(t);
out.writeBigInteger(q);
out.writeBigInteger(p);
out.writeBigInteger(g);
out.writeBigInteger(y);
return out.toByteArray();
}
private void exchangeKeys() {
try {
output.write(modulus.toByteArray());
byte[] buffer = new byte[ciphertextBlockSize];
input.read(buffer);
recipModulus = new BigInteger(1, buffer);
} catch (IOException ioe) {
System.err.println("Error establishing keys");
}
}
public static String md5(File file)
throws NoSuchAlgorithmException, FileNotFoundException, IOException {
MessageDigest md = MessageDigest.getInstance("MD5");
InputStream is = new FileInputStream(file);
byte[] buffer = new byte[8192];
int read = 0;
while ((read = is.read(buffer)) > 0) md.update(buffer, 0, read);
byte[] md5 = md.digest();
BigInteger bi = new BigInteger(1, md5);
is.close();
String hex = bi.toString(16);
while (hex.length() < 32) {
hex = "0" + hex;
} // Padding
return hex;
}
static byte[] buildDH(DHPublicKey key) {
DataByteOutputStream out = new DataByteOutputStream();
BigInteger p = key.getParams().getP();
BigInteger g = key.getParams().getG();
BigInteger y = key.getY();
int pLength, gLength, yLength;
if (g.equals(TWO) && (p.equals(DHPRIME768) || p.equals(DHPRIME1024))) {
pLength = 1;
gLength = 0;
} else {
pLength = BigIntegerLength(p);
gLength = BigIntegerLength(g);
}
yLength = BigIntegerLength(y);
out.writeShort(pLength);
if (pLength == 1) {
if (p.bitLength() == 768) out.writeByte((byte) 1);
else out.writeByte((byte) 2);
} else out.writeBigInteger(p);
out.writeShort(gLength);
if (gLength > 0) out.writeBigInteger(g);
out.writeShort(yLength);
out.writeBigInteger(y);
return out.toByteArray();
}
private void makeKeys() {
PrimeGenerator pg = new PrimeGenerator(513, 10, sr);
do {
p = pg.getStrongPrime();
} while (p.subtract(BigIntegerMath.ONE).mod(BigIntegerMath.THREE).equals(BigIntegerMath.ZERO));
do {
q = pg.getStrongPrime();
} while (q.subtract(BigIntegerMath.ONE).mod(BigIntegerMath.THREE).equals(BigIntegerMath.ZERO));
modulus = p.multiply(q);
// Use 3 as enciphering exponent - OK since we are using salt
decipherExp =
BigIntegerMath.THREE.modInverse(
p.subtract(BigIntegerMath.ONE).multiply(q.subtract(BigIntegerMath.ONE)));
ciphertextBlockSize = (modulus.bitLength() - 1) / 8 + 1;
// Maximum size of plaintext is 6 bytes less than ciphertext
// 1 to get under modulus
// 4 for the salt
// 1 for a pad byte
plaintextBlockSize = ciphertextBlockSize - 6;
}
static int BigIntegerLength(BigInteger i) {
byte[] b = i.toByteArray();
return (b[0] == 0 ? b.length - 1 : b.length);
}
public class Main {
/**
* Static variables for 1024 bit Diffie-Hellman algorithm.
*
* <p>This is required to have matching moduli between client and server.
*/
private static final byte SKIP_1024_MODULUS_BYTES[] = {
(byte) 0xF4, (byte) 0x88, (byte) 0xFD, (byte) 0x58,
(byte) 0x4E, (byte) 0x49, (byte) 0xDB, (byte) 0xCD,
(byte) 0x20, (byte) 0xB4, (byte) 0x9D, (byte) 0xE4,
(byte) 0x91, (byte) 0x07, (byte) 0x36, (byte) 0x6B,
(byte) 0x33, (byte) 0x6C, (byte) 0x38, (byte) 0x0D,
(byte) 0x45, (byte) 0x1D, (byte) 0x0F, (byte) 0x7C,
(byte) 0x88, (byte) 0xB3, (byte) 0x1C, (byte) 0x7C,
(byte) 0x5B, (byte) 0x2D, (byte) 0x8E, (byte) 0xF6,
(byte) 0xF3, (byte) 0xC9, (byte) 0x23, (byte) 0xC0,
(byte) 0x43, (byte) 0xF0, (byte) 0xA5, (byte) 0x5B,
(byte) 0x18, (byte) 0x8D, (byte) 0x8E, (byte) 0xBB,
(byte) 0x55, (byte) 0x8C, (byte) 0xB8, (byte) 0x5D,
(byte) 0x38, (byte) 0xD3, (byte) 0x34, (byte) 0xFD,
(byte) 0x7C, (byte) 0x17, (byte) 0x57, (byte) 0x43,
(byte) 0xA3, (byte) 0x1D, (byte) 0x18, (byte) 0x6C,
(byte) 0xDE, (byte) 0x33, (byte) 0x21, (byte) 0x2C,
(byte) 0xB5, (byte) 0x2A, (byte) 0xFF, (byte) 0x3C,
(byte) 0xE1, (byte) 0xB1, (byte) 0x29, (byte) 0x40,
(byte) 0x18, (byte) 0x11, (byte) 0x8D, (byte) 0x7C,
(byte) 0x84, (byte) 0xA7, (byte) 0x0A, (byte) 0x72,
(byte) 0xD6, (byte) 0x86, (byte) 0xC4, (byte) 0x03,
(byte) 0x19, (byte) 0xC8, (byte) 0x07, (byte) 0x29,
(byte) 0x7A, (byte) 0xCA, (byte) 0x95, (byte) 0x0C,
(byte) 0xD9, (byte) 0x96, (byte) 0x9F, (byte) 0xAB,
(byte) 0xD0, (byte) 0x0A, (byte) 0x50, (byte) 0x9B,
(byte) 0x02, (byte) 0x46, (byte) 0xD3, (byte) 0x08,
(byte) 0x3D, (byte) 0x66, (byte) 0xA4, (byte) 0x5D,
(byte) 0x41, (byte) 0x9F, (byte) 0x9C, (byte) 0x7C,
(byte) 0xBD, (byte) 0x89, (byte) 0x4B, (byte) 0x22,
(byte) 0x19, (byte) 0x26, (byte) 0xBA, (byte) 0xAB,
(byte) 0xA2, (byte) 0x5E, (byte) 0xC3, (byte) 0x55,
(byte) 0xE9, (byte) 0x2F, (byte) 0x78, (byte) 0xC7
};
// In oder to use skip, we need a BigInteger representation of that modulus
private static final BigInteger MODULUS = new BigInteger(1, SKIP_1024_MODULUS_BYTES);
// We also need a base for Dittie-Hellman, which SKIP defines as 2
private static final BigInteger BASE = BigInteger.valueOf(2);
// we can wrap those two SKIP parameter into one DHParamterSpec, which we'll use to initialize our
// keyAgreement latger
private static final DHParameterSpec PARAMETER_SPEC = new DHParameterSpec(MODULUS, BASE);
public static void main(String[] args) throws Exception {
// prompt user to enter a port number
System.out.print("Enter the port number: ");
Scanner scan = new Scanner(System.in);
int port = scan.nextInt();
scan.nextLine();
System.out.print("Enter the host name: ");
String hostName = scan.nextLine();
// Initialize a key pair generator with the SKIP parameters we sepcified, and genrating a pair
// This will take a while: 5...15 seconrds
System.out.println("Generating a Diffie-Hellman keypair: ");
KeyPairGenerator kpg = KeyPairGenerator.getInstance("DH");
kpg.initialize(PARAMETER_SPEC);
KeyPair keyPair = kpg.genKeyPair();
System.out.println("key pair has been made...");
// one the key pair has been generated, we want to listen on
// a given port for a connection to come in
// once we get a connection, we will get two streams, One for input
// and one for output
// open a port and wait for a connection
ServerSocket ss = new ServerSocket(port);
System.out.println("Listeining on port " + port + " ...");
Socket socket = ss.accept();
// use to output and input primitive data type
DataOutputStream out = new DataOutputStream(socket.getOutputStream());
// next thing to do is send our public key and receive client's
// this corresponds to server step 3 and step 4 in the diagram
System.out.println("Sending my public key...");
byte[] keyBytes = keyPair.getPublic().getEncoded();
out.writeInt(keyBytes.length);
out.write(keyBytes);
System.out.println("Server public key bytes: " + CryptoUtils.toHex(keyBytes));
// receive the client's public key
System.out.println("Receiving client's public key...");
DataInputStream in = new DataInputStream(socket.getInputStream());
keyBytes = new byte[in.readInt()];
in.readFully(keyBytes);
// create client's public key
KeyFactory kf = KeyFactory.getInstance("DH");
X509EncodedKeySpec x509Spec = new X509EncodedKeySpec(keyBytes);
PublicKey clientPublicKey = kf.generatePublic(x509Spec);
// print out client's public key bytes
System.out.println(
"Client public key bytes: " + CryptoUtils.toHex(clientPublicKey.getEncoded()));
// we can now use the client's public key and
// our own private key to perform the key agreement
System.out.println("Performing the key agreement ... ");
KeyAgreement ka = KeyAgreement.getInstance("DH");
ka.init(keyPair.getPrivate());
ka.doPhase(clientPublicKey, true);
// in a chat application, each character is sendt over the wire, separetly encrypted,
// Instead of using ECB, we are goin to use CFB, with a block size of 8 bits(1byte)
// to send each character. We will encrypt the same character in a different way
// each time. But in order to use CFB8, we need an IVof 8 bytes. We will create
// that IV randomly and and send it to the client. It doesn't matter if somoene
// eavesdrops on the IV when it is sent over the wire. it's not sensitive info
// creating the IV and sending it corresponds to step 6 and 7
byte[] iv = new byte[8];
SecureRandom sr = new SecureRandom();
sr.nextBytes(iv);
out.write(iv);
// we generate the secret byte array we share with the client and use it
// to create the session key (Step 8)
byte[] sessionKeyBytes = ka.generateSecret();
// create the session key
SecretKeyFactory skf = SecretKeyFactory.getInstance("DESede");
DESedeKeySpec DESedeSpec = new DESedeKeySpec(sessionKeyBytes);
SecretKey sessionKey = skf.generateSecret(DESedeSpec);
// printout session key bytes
System.out.println("Session key bytes: " + CryptoUtils.toHex(sessionKey.getEncoded()));
// now use tha that session key and IV to create a CipherInputStream. We will use them to read
// all character
// that are sent to us by the client
System.out.println("Creating the cipher stream ...");
Cipher decrypter = Cipher.getInstance("DESede/CFB8/NoPadding");
IvParameterSpec spec = new IvParameterSpec(iv);
decrypter.init(Cipher.DECRYPT_MODE, sessionKey, spec);
CipherInputStream cipherIn = new CipherInputStream(socket.getInputStream(), decrypter);
// we just keep reading the input and print int to the screen, until -1 sent over
int theCharacter = 0;
theCharacter = cipherIn.read();
while (theCharacter != -1) {
System.out.print((char) theCharacter);
theCharacter = cipherIn.read();
}
// once -1 is received we want to close up our stream and exit
cipherIn.close();
in.close();
out.close();
socket.close();
}
}
