java.security.interfaces

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1. Verifying a Digital Signature

import java.security.KeyFactory;
import java.security.PublicKey;
import java.security.Signature;
import java.security.spec.X509EncodedKeySpec;

public class VerifySignature {

    public static boolean verify(byte[] signatureBytes, byte[] message, PublicKey publicKey) throws Exception {
        Signature signature = Signature.getInstance("SHA256withRSA");
        signature.initVerify(publicKey);
        signature.update(message);
        return signature.verify(signatureBytes);
    }
}

2. Encrypting a Secret Key Using a Public Key

import java.security.Cipher;
import java.security.KeyFactory;
import java.security.PublicKey;
import java.security.spec.X509EncodedKeySpec;

public class EncryptSecretKey {

    public static byte[] encrypt(byte[] secretKey, PublicKey publicKey) throws Exception {
        Cipher cipher = Cipher.getInstance("RSA");
        cipher.init(Cipher.ENCRYPT_MODE, publicKey);
        return cipher.doFinal(secretKey);
    }
}

3. Decrypting a Secret Key Using a Private Key

import java.security.Cipher;
import java.security.KeyFactory;
import java.security.PrivateKey;
import java.security.spec.PKCS8EncodedKeySpec;

public class DecryptSecretKey {

    public static byte[] decrypt(byte[] encryptedSecretKey, PrivateKey privateKey) throws Exception {
        Cipher cipher = Cipher.getInstance("RSA");
        cipher.init(Cipher.DECRYPT_MODE, privateKey);
        return cipher.doFinal(encryptedSecretKey);
    }
}

4. Generating a Diffie-Hellman Key Pair

import java.security.KeyPairGenerator;
import java.security.spec.DHParameterSpec;

public class GenerateDHKeyPair {

    public static void generate() throws Exception {
        KeyPairGenerator keyGenerator = KeyPairGenerator.getInstance("DH");
        DHParameterSpec dhParameterSpec = new DHParameterSpec(2048, 1);
        keyGenerator.initialize(dhParameterSpec);
        KeyPair keyPair = keyGenerator.generateKeyPair();
    }
}

5. Calculating the Diffie-Hellman Secret

import java.security.KeyPair;
import java.security.spec.DHParameterSpec;

public class CalculateDHSecret {

    public static byte[] calculate(KeyPair keyPair1, PublicKey keyPair2, DHParameterSpec dhParameterSpec) throws Exception {
        byte[] secret1 = keyPair1.getPrivate().calculateSecret(keyPair2.getPublic(), dhParameterSpec);
        byte[] secret2 = keyPair2.getPrivate().calculateSecret(keyPair1.getPublic(), dhParameterSpec);
        return secret1; // Should be same as secret2
    }
}

6. Generating an RSA Key Pair

import java.security.KeyPairGenerator;

public class GenerateRSAKeyPair {

    public static void generate() throws Exception {
        KeyPairGenerator keyGenerator = KeyPairGenerator.getInstance("RSA");
        keyGenerator.initialize(2048);
        KeyPair keyPair = keyGenerator.generateKeyPair();
    }
}

7. Generating an AES Key Pair

import java.security.KeyGenerator;

public class GenerateAESKeyPair {

    public static void generate() throws Exception {
        KeyGenerator keyGenerator = KeyGenerator.getInstance("AES");
        keyGenerator.init(256);
        keyGenerator.generateKey();
    }
}

8. Encrypting Data with an AES Key

import java.security.Cipher;

public class EncryptAES {

    public static byte[] encrypt(byte[] data, byte[] key) throws Exception {
        Cipher cipher = Cipher.getInstance("AES/ECB/NoPadding");
        cipher.init(Cipher.ENCRYPT_MODE, new SecretKeySpec(key, "AES"));
        return cipher.doFinal(data);
    }
}

9. Decrypting Data with an AES Key

import java.security.Cipher;

public class DecryptAES {

    public static byte[] decrypt(byte[] data, byte[] key) throws Exception {
        Cipher cipher = Cipher.getInstance("AES/ECB/NoPadding");
        cipher.init(Cipher.DECRYPT_MODE, new SecretKeySpec(key, "AES"));
        return cipher.doFinal(data);
    }
}

10. Hashing Data with SHA-256

import java.security.MessageDigest;

public class HashSHA256 {

    public static byte[] hash(byte[] data) throws Exception {
        MessageDigest digest = MessageDigest.getInstance("SHA-256");
        return digest.digest(data);
    }
}

11. Signing Data with an RSA Private Key

import java.security.Signature;

public class SignRSA {

    public static byte[] sign(byte[] data, PrivateKey privateKey) throws Exception {
        Signature signature = Signature.getInstance("SHA256withRSA");
        signature.initSign(privateKey);
        signature.update(data);
        return signature.sign();
    }
}

12. Verifying a Signature with an RSA Public Key

import java.security.Signature;

public class VerifyRSA {

    public static boolean verify(byte[] signatureBytes, byte[] data, PublicKey publicKey) throws Exception {
        Signature signature = Signature.getInstance("SHA256withRSA");
        signature.initVerify(publicKey);
        signature.update(data);
        return signature.verify(signatureBytes);
    }
}

13. Generating an ECDSA Key Pair

import java.security.KeyPairGenerator;

public class GenerateECDSAKeyPair {

    public static void generate() throws Exception {
        KeyPairGenerator keyGenerator = KeyPairGenerator.getInstance("EC");
        keyGenerator.initialize(256);
        KeyPair keyPair = keyGenerator.generateKeyPair();
    }
}

14. Signing Data with an ECDSA Private Key

import java.security.Signature;

public class SignECDSA {

    public static byte[] sign(byte[] data, PrivateKey privateKey) throws Exception {
        Signature signature = Signature.getInstance("SHA256withECDSA");
        signature.initSign(privateKey);
        signature.update(data);
        return signature.sign();
    }
}

15. Verifying a Signature with an ECDSA Public Key

import java.security.Signature;

public class VerifyECDSA {

    public static boolean verify(byte[] signatureBytes, byte[] data, PublicKey publicKey) throws Exception {
        Signature signature = Signature.getInstance("SHA256withECDSA");
        signature.initVerify(publicKey);
        signature.update(data);
        return signature.verify(signatureBytes);
    }
}

16. Generating a DSA Key Pair

import java.security.KeyPairGenerator;

public class GenerateDSAKeyPair {

    public static void generate() throws Exception {
        KeyPairGenerator keyGenerator = KeyPairGenerator.getInstance("DSA");
        keyGenerator.initialize(1024);
        KeyPair keyPair = keyGenerator.generateKeyPair();
    }
}

17. Signing Data with a DSA Private Key

import java.security.Signature;

public class SignDSA {

    public static byte[] sign(byte[] data, PrivateKey privateKey) throws Exception {
        Signature signature = Signature.getInstance("SHA256withDSA");
        signature.initSign(privateKey);
        signature.update(data);
        return signature.sign();
    }
}

18. Verifying a Signature with a DSA Public Key

import java.security.Signature;

public class VerifyDSA {

    public static boolean verify(byte[] signatureBytes, byte[] data, PublicKey publicKey) throws Exception {
        Signature signature = Signature.getInstance("SHA256withDSA");
        signature.initVerify(publicKey);
        signature.update(data);
        return signature.verify(signatureBytes);
    }
}

19. Generating a DH Key Pair

import java.security.KeyPairGenerator;

public class GenerateDHKeyPair {

    public static void generate() throws Exception {
        KeyPairGenerator keyGenerator = KeyPairGenerator.getInstance("DH");
        keyGenerator.initialize(2048);
        KeyPair keyPair = keyGenerator.generateKeyPair();
    }
}

20. Agreeing on a Secret Key with DH

import java.security.KeyPair;

public class AgreeDHSecret {

    public static byte[] agree(KeyPair keyPair1, PublicKey keyPair2) throws Exception {
        byte[] secret1 = keyPair1.getPrivate().calculateSecret(keyPair2.getPublic());
        byte[] secret2 = keyPair2.getPrivate().calculateSecret(keyPair1.getPublic());
        return secret1; // Should be same as secret2
    }
}

21. Generating an ElGamal Key Pair

import java.security.KeyPairGenerator;

public class GenerateElGamalKeyPair {

    public static void generate() throws Exception {
        KeyPairGenerator keyGenerator = KeyPairGenerator.getInstance("ElGamal");
        keyGenerator.initialize(2048);
        KeyPair keyPair = keyGenerator.generateKeyPair();
    }
}

22. Encrypting Data with an ElGamal Public Key

import java.security.Cipher;

public class EncryptElGamal {

    public static byte[] encrypt(byte[] data, PublicKey publicKey) throws Exception {
        Cipher cipher = Cipher.getInstance("ElGamal");
        cipher.init(Cipher.ENCRYPT_MODE, publicKey);
        return cipher.doFinal(data);
    }
}

23. Decrypting Data with an ElGamal Private Key

import java.security.Cipher;

public class DecryptElGamal {

    public static byte[] decrypt(byte[] data, PrivateKey privateKey) throws Exception {
        Cipher cipher = Cipher.getInstance("ElGamal");
        cipher.init(Cipher.DECRYPT_MODE, privateKey);
        return cipher.doFinal(data);
    }
}

24. Generating a DES Key Pair

import java.security.KeyGenerator;

public class GenerateDESKeyPair {

    public static void generate() throws Exception {
        KeyGenerator keyGenerator = KeyGenerator.getInstance("DES");
        keyGenerator.init(56);
        keyGenerator.generateKey();
    }
}

25. Encrypting Data with a DES Key

import java.security.Cipher;

public class EncryptDES {

    public static byte[] encrypt(byte[] data, byte[] key) throws Exception {
        Cipher cipher = Cipher.getInstance("DES/ECB/NoPadding");
        cipher.init(Cipher.ENCRYPT_MODE, new SecretKeySpec(key, "DES"));
        return cipher.doFinal(data);
    }
}

26. Decrypting Data with a DES Key

import java.security.Cipher;

public class DecryptDES {

    public static byte[] decrypt(byte[] data, byte[] key) throws Exception {
        Cipher cipher = Cipher.getInstance("DES/ECB/NoPadding");
        cipher.init(Cipher.DECRYPT_MODE, new SecretKeySpec(key, "DES"));
        return cipher.doFinal(data);
    }
}

27. Generating a TripleDES Key Pair

import java.security.KeyGenerator;

public class GenerateTripleDESKeyPair {

    public static void generate() throws Exception {
        KeyGenerator keyGenerator = KeyGenerator.getInstance("TripleDES");
        keyGenerator.init(168);
        keyGenerator.generateKey();
    }
}

28. Encrypting Data with a TripleDES Key

import java.security.Cipher;

public class EncryptTripleDES {

    public static byte[] encrypt(byte[] data, byte[] key) throws Exception {
        Cipher cipher = Cipher.getInstance("TripleDES/ECB/NoPadding");
        cipher.init(Cipher.ENCRYPT_MODE, new SecretKeySpec(key, "TripleDES"));
        return cipher.doFinal(data);
    }
}

29. Decrypting Data with a TripleDES Key