Java中的非对称加密密码学

// Java program to create a
// asymmetric key

package java_cryptography;
import java.security.KeyPair;
import java.security
	.KeyPairGenerator;
import java.security
	.SecureRandom;
import javax.xml.bind
	.DatatypeConverter;

// Class to create an asymmetric key
public class Asymmetric {

	private static final String RSA
		= "RSA";

	// Generating public and private keys
	// using RSA algorithm.
	public static KeyPair generateRSAKkeyPair()
		throws Exception
	{
		SecureRandom secureRandom
			= new SecureRandom();

		KeyPairGenerator keyPairGenerator
			= KeyPairGenerator.getInstance(RSA);

		keyPairGenerator.initialize(
			2048, secureRandom);

		return keyPairGenerator
			.generateKeyPair();
	}

	// Driver code
	public static void main(String args[])
		throws Exception
	{
		KeyPair keypair
			= generateRSAKkeyPair();

		System.out.println(
			"Public Key is: "
			+ DatatypeConverter.printHexBinary(
				keypair.getPublic().getEncoded()));

		System.out.println(
			"Private Key is: "
			+ DatatypeConverter.printHexBinary(
				keypair.getPrivate().getEncoded()));
	}
}

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// Java program to perform the
// encryption and decryption
// using asymmetric key

package java_cryptography;
import java.security.KeyPair;
import java.security.KeyPairGenerator;
import java.security.PrivateKey;
import java.security.PublicKey;
import java.security.SecureRandom;
import java.util.Scanner;

import javax.crypto.Cipher;
import javax.xml.bind
	.DatatypeConverter;

public class Asymmetric {

	private static final String RSA
		= "RSA";
	private static Scanner sc;

	// Generating public & private keys
	// using RSA algorithm.
	public static KeyPair generateRSAKkeyPair()
		throws Exception
	{
		SecureRandom secureRandom = new SecureRandom();
		KeyPairGenerator keyPairGenerator
			= KeyPairGenerator.getInstance(RSA);

		keyPairGenerator.initialize(
			2048, secureRandom);
		return keyPairGenerator
			.generateKeyPair();
	}

	// Encryption function which converts
	// the plainText into a cipherText
	// using private Key.
	public static byte[] do_RSAEncryption(
		String plainText,
		PrivateKey privateKey)
		throws Exception
	{
		Cipher cipher = Cipher.getInstance(RSA);
		cipher.init(Cipher.ENCRYPT_MODE, privateKey);
		return cipher.doFinal(
			plainText.getBytes());
	}

	// Decryption function which converts
	// the ciphertext back to the
	// original plaintext.
	public static String do_RSADecryption(
		byte[] cipherText,
		PublicKey publicKey)
		throws Exception
	{
		Cipher cipher
			= Cipher.getInstance(RSA);

		cipher.init(Cipher.DECRYPT_MODE,
					publicKey);
		byte[] result
			= cipher.doFinal(cipherText);

		return new String(result);
	}

	// Driver code
	public static void main(String args[])
		throws Exception
	{
		KeyPair keypair
			= generateRSAKkeyPair();

		String plainText = "This is the PlainText "+ "I want to Encrypt using RSA.";

		byte[] cipherText
			= do_RSAEncryption(
				plainText,
				keypair.getPrivate());

		System.out.println(
			"The Public Key is: "
			+ DatatypeConverter.printHexBinary(
				keypair.getPublic().getEncoded()));

		System.out.println(
			"The Private Key is: "
			+ DatatypeConverter.printHexBinary(
				keypair.getPrivate().getEncoded()));

		System.out.print("The Encrypted Text is: ");

		System.out.println(
			DatatypeConverter.printHexBinary(
				cipherText));

		String decryptedText
			= do_RSADecryption(
				cipherText,
				keypair.getPublic());

		System.out.println(
			"The decrypted text is: "
			+ decryptedText);
	}
}

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