store wallet with password protection, basic miner class

.gitignore

@@ -1,4 +1,5 @@
 logs/
+keys/
 
 target/
 !.mvn/wrapper/maven-wrapper.jar

src/main/java/hu/saborsoft/blockchain/example/wallet/WalletExample1.java

@@ -0,0 +1,25 @@
+package hu.saborsoft.blockchain.example.wallet;
+
+import hu.saborsoft.blockchain.support.EncryptionAlgorithm;
+import hu.saborsoft.blockchain.wallet.Wallet;
+
+import java.util.Scanner;
+
+public class WalletExample1 {
+
+    public static void main(String[] args) {
+        Scanner in = new Scanner(System.in);
+        System.out.println("To create a wallet, please give your name");
+        String name = in.nextLine();
+        System.out.println("please create a password");
+        String password = in.nextLine();
+        in.close();
+        Wallet w = new Wallet(name, password, EncryptionAlgorithm.AES);
+        System.out.println("wallet created for " + w.getName());
+
+        // let's load this wallet
+        Wallet w2 = new Wallet(name, password, EncryptionAlgorithm.AES);
+        System.out.println("wallet loaded successfully, wallet name=" + w2.getName());
+    }
+
+}

src/main/java/hu/saborsoft/blockchain/support/EncryptionAlgorithm.java

@@ -0,0 +1,5 @@
+package hu.saborsoft.blockchain.support;
+
+public enum EncryptionAlgorithm {
+    XOR, AES
+}

src/main/java/hu/saborsoft/blockchain/support/UtilityMethods.java

@@ -158,6 +158,20 @@ public static void displayTransaction(Transaction t, PrintStream out, int level)
         displayTab(out, level, "}");
     }
 
+    public static byte[] encrypt(byte[] key, String password, EncryptionAlgorithm algo) {
+        return switch (algo) {
+            case XOR -> encryptionByXOR(key, password);
+            case AES -> encryptionByAES(key, password);
+        };
+    }
+
+    public static byte[] decrypt(byte[] key, String password, EncryptionAlgorithm algo) {
+        return switch (algo) {
+            case XOR -> decryptionByXOR(key, password);
+            case AES -> decryptionByAES(key, password);
+        };
+    }
+
     public static byte[] encryptionByXOR(byte[] key, String password) {
         int more = 100;
         byte[] p = messageDigestSHA256ToBytes(password);
@@ -204,7 +218,6 @@ public static byte[] decryptionByXOR(FileInputStream keyIn, String password) {
         }
     }
 
-
     public static byte[] encryptionByAES(byte[] key, String password) {
         try {
             byte[] salt = new byte[8];

src/main/java/hu/saborsoft/blockchain/wallet/Miner.java

@@ -0,0 +1,15 @@
+package hu.saborsoft.blockchain.wallet;
+
+import hu.saborsoft.blockchain.block.Block;
+
+public class Miner extends Wallet {
+
+    public Miner(String minerName, String password) {
+        super(minerName, password);
+    }
+
+    public boolean mineBlock(Block block) {
+        return block.mineTheBlock();
+    }
+
+}

src/main/java/hu/saborsoft/blockchain/wallet/Wallet.java

@@ -1,20 +1,41 @@
 package hu.saborsoft.blockchain.wallet;
 
+import hu.saborsoft.blockchain.support.EncryptionAlgorithm;
 import hu.saborsoft.blockchain.support.UtilityMethods;
 
+import java.io.*;
 import java.security.KeyPair;
 import java.security.PrivateKey;
 import java.security.PublicKey;
 
 public class Wallet {
 
+    private static final String KEY_LOCATION = "keys";
+
     private KeyPair keyPair;
 
     private String walletName;
 
-    public Wallet(String walletName) {
-        keyPair = UtilityMethods.generateKeyPair(2048);
+    public Wallet(String walletName, String password) {
+        this(walletName, password, EncryptionAlgorithm.AES);
+    }
+
+    public Wallet(String walletName, String password, EncryptionAlgorithm algo) {
+        keyPair = UtilityMethods.generateKeyPair();
         this.walletName = walletName;
+        try {
+            populateExistingWallet(password, algo);
+            System.out.println("A wallet exists with the same name "
+                    + "and password. Loaded the existing wallet");
+        } catch (Exception ee) {
+            try {
+                prepareWallet(password, algo);
+                System.out.println("Created a new wallet based on "
+                        + "the name and password");
+            } catch (IOException ioe) {
+                throw new RuntimeException(ioe);
+            }
+        }
     }
 
     public String getName() {
@@ -29,4 +50,37 @@ public PrivateKey getPrivateKey() {
         return keyPair.getPrivate();
     }
 
+    private void prepareWallet(String password, EncryptionAlgorithm algo) throws IOException {
+        ByteArrayOutputStream bo = new ByteArrayOutputStream();
+        ObjectOutputStream out = new ObjectOutputStream(bo);
+        out.writeObject(this.keyPair);
+        byte[] keyBytes = UtilityMethods.encrypt(bo.toByteArray(), password, algo);
+        File f = new File(KEY_LOCATION);
+        if (!f.exists()) {
+            f.mkdir();
+        }
+        FileOutputStream fout = new FileOutputStream(getFilePath());
+        fout.write(keyBytes);
+        fout.close();
+        bo.close();
+    }
+
+    private void populateExistingWallet(String password, EncryptionAlgorithm algo) throws IOException, ClassNotFoundException {
+        FileInputStream fin = new FileInputStream(getFilePath());
+        byte[] bb = new byte[4096];
+        int size = fin.read(bb);
+        fin.close();
+        byte[] data = new byte[size];
+        for (int i = 0; i < data.length; i++) {
+            data[i] = bb[i];
+        }
+        byte[] keyBytes = UtilityMethods.decrypt(data, password, algo);
+        ObjectInputStream in = new ObjectInputStream(new ByteArrayInputStream(keyBytes));
+        keyPair = (KeyPair) in.readObject();
+    }
+
+    private String getFilePath() {
+        return KEY_LOCATION + "/" + getName().replace(" ", "_") + "_keys";
+    }
+
 }