Naaturel/masi-symmetric-cypher
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Step 1 completed

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This commit is contained in:
Laurent
2025-10-24 19:32:34 +02:00
parent 6283519edb
commit d0eb17f772
1 changed files with 80 additions and 23 deletions
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103
src/main/java/step1/Main.java
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@@ -3,6 +3,7 @@ package step1;
import javax.crypto.Cipher;
import javax.crypto.KeyGenerator;
import javax.crypto.SecretKey;
import javax.crypto.spec.GCMParameterSpec;
import javax.crypto.spec.IvParameterSpec;
import javax.crypto.spec.SecretKeySpec;
import java.io.*;
@@ -23,7 +24,6 @@ public class Main {
try (Socket socket = new Socket()) {
socket.connect(new InetSocketAddress("127.0.0.1", 8888));
//Saving the buffer reference to read it later
@@ -33,40 +33,78 @@ public class Main {
//Waiting for welcome message so it does
//not pollute the fucking stream
String welcome = readResponse(reader);
System.out.println("Welcome message: " + welcome);
displayReceived("Welcome message: " + welcome);
//Creating the key
SecretKey key = get3DESKey();
byte[] encodedKey = key.getEncoded();
String base64Key = Base64.getEncoder().encodeToString(encodedKey);
displayInfo("Generated key: " + base64Key);
//Sending the key
send(socket, base64Key);
System.out.println("Key sent to server.");
displaySent("Key sent to server : " + base64Key);
//Reading the message sent by the server
String text = readResponse(reader);
System.out.println("Received message: " + text);
displayReceived("Received message: " + text);
//Encrypting the message
byte[] encryptedMessage = encrypt(key, text);
String base64Message = Base64.getEncoder().encodeToString(encryptedMessage);
System.out.println("Encrypted message to send : " + base64Message);
displayInfo("Encrypted message : " + base64Message);
//Sending encrypted message
send(socket, base64Message);
System.out.println("Encrypted message sent to server.");
displaySent("Encrypted message sent to server : " + base64Message);
//Reading the parameters sent by the server
String parameters = readResponse(reader);
System.out.println("Received parameters: " + parameters);
//Reading the base 64 key sent by the server
String receivedKey = readResponse(reader);
displayReceived("Received base64 key: " + receivedKey);
//Reading the base 64 IV sent by the server
String base64IV = readResponse(reader);
displayReceived("Received base 64 IV: " + base64IV);
//Reading the AAD sent by the server
String AAD = readResponse(reader);
displayReceived("Received AAD: " + AAD);
//Reading the base 64 encrypted message sent by the server
String base64ReceivedMessage = readResponse(reader);
displayReceived("Received base 64 encrypted message: " + base64ReceivedMessage);
String decryptedMessage = decrypt(receivedKey, base64IV, AAD, base64ReceivedMessage);
displayInfo("Decrypted message : " + decryptedMessage);
send(socket, decryptedMessage);
displaySent("Decrypted message sent to server : " + decryptedMessage);
displayInfo("Process completed. Check out the server output to know if it was successful.");
} catch (Exception e) {
e.printStackTrace();
}
}
public static void displayInfo(String message){
final String BLUE = "\u001B[34m";
final String RESET = "\u001B[0m";
System.out.println(BLUE + "Info >>> " + message + RESET);
}
public static void displayReceived(String message){
String GREEN = "\u001B[32m";
String RESET = "\u001B[0m";
System.out.println(GREEN + "Received >>> " + message + RESET);
}
public static void displaySent(String message){
final String RED = "\u001B[31m";
final String RESET = "\u001B[0m";
System.out.println(RED + "Sent >>> " + message + RESET);
}
public static void send(Socket socket, String data) throws IOException {
OutputStream output = socket.getOutputStream();
output.write(String.format("%s\r\n", data).getBytes(StandardCharsets.UTF_8));
@@ -91,24 +129,43 @@ public class Main {
}
public static String decrypt(byte[] keyBytes, String base64IvAndCiphertext) throws Exception {
SecretKey key = new SecretKeySpec(keyBytes, ALGORITHM);
public static String decrypt(String base64Key, String base64IV, String aad, String base64Ciphertext) throws Exception {
byte[] ivPlusCipher = Base64.getDecoder().decode(base64IvAndCiphertext);
if (ivPlusCipher.length < 8) throw new IllegalArgumentException("Data too short");
final int GCM_TAG_LENGTH = 128;
byte[] iv = new byte[8];
System.arraycopy(ivPlusCipher, 0, iv, 0, 8);
IvParameterSpec ivSpec = new IvParameterSpec(iv);
// Decode Base64 inputs
byte[] key = Base64.getDecoder().decode(base64Key);
byte[] iv = Base64.getDecoder().decode(base64IV);
byte[] cipherMessage = Base64.getDecoder().decode(base64Ciphertext);
byte[] ciphertext = new byte[ivPlusCipher.length - 8];
System.arraycopy(ivPlusCipher, 8, ciphertext, 0, ciphertext.length);
// Split ciphertext and authentication tag (last 16 bytes)
int tagLength = GCM_TAG_LENGTH / 8;
int ciphertextLength = cipherMessage.length - tagLength;
byte[] ciphertext = new byte[ciphertextLength];
byte[] tag = new byte[tagLength];
Cipher cipher = Cipher.getInstance(TRANSFORMATION);
cipher.init(Cipher.DECRYPT_MODE, key, ivSpec);
System.arraycopy(cipherMessage, 0, ciphertext, 0, ciphertextLength);
System.arraycopy(cipherMessage, ciphertextLength, tag, 0, tagLength);
byte[] plaintextBytes = cipher.doFinal(ciphertext);
return new String(plaintextBytes, StandardCharsets.UTF_8);
// Combine ciphertext + tag
byte[] ciphertextWithTag = new byte[cipherMessage.length];
System.arraycopy(cipherMessage, 0, ciphertextWithTag, 0, cipherMessage.length);
// Create AES key and GCM spec
SecretKeySpec keySpec = new SecretKeySpec(key, "AES");
GCMParameterSpec gcmSpec = new GCMParameterSpec(GCM_TAG_LENGTH, iv);
// Initialize cipher
Cipher cipher = Cipher.getInstance("AES/GCM/NoPadding");
cipher.init(Cipher.DECRYPT_MODE, keySpec, gcmSpec);
// Add AAD (if any)
if (aad != null && !aad.isEmpty()) {
cipher.updateAAD(aad.getBytes());
}
// Decrypt and return plaintext
byte[] plaintext = cipher.doFinal(ciphertextWithTag);
return new String(plaintext, "UTF-8");
}
}