rsa算法实现java

RSA算法是常用的非对称加密算法，以下是Java实现RSA算法的示例代码：

import java.security.KeyPair;
import java.security.KeyPairGenerator;
import java.security.NoSuchAlgorithmException;
import java.security.PrivateKey;
import java.security.PublicKey;
import javax.crypto.Cipher;

public class RSAEncryptionExample {
    public static void main(String[] args) throws Exception {
        String plainText = "Hello, world!";
        KeyPair keyPair = generateKeyPair();

        // 加密
        byte[] cipherText = encrypt(plainText, keyPair.getPublic());
        System.out.println("Cipher text: " + new String(cipherText));

        // 解密
        String decryptedText = decrypt(cipherText, keyPair.getPrivate());
        System.out.println("Decrypted text: " + decryptedText);
    }

    public static KeyPair generateKeyPair() throws NoSuchAlgorithmException {
        KeyPairGenerator keyPairGenerator = KeyPairGenerator.getInstance("RSA");
        keyPairGenerator.initialize(2048);
        return keyPairGenerator.generateKeyPair();
    }

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

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

以上代码中，`generateKeyPair`方法用于生成密钥对，`encrypt`方法用于加密，`decrypt`方法用于解密。其中，加密和解密都使用了`Cipher`类来完成。在实际使用中，需要注意安全性和效率问题。