用Java 写出RSA使用公钥解密的方法

好的，以下是使用Java写出RSA使用公钥解密的方法：

import java.security.*;
import java.security.spec.*;
import javax.crypto.*;
import javax.crypto.spec.*;
import java.util.Base64;

public class RSADecryptionExample {
  private static final String PUBLIC_KEY_STRING = "MIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEAjRcaCJES+VPnOdJ7dSNPctoMC67ix5ju5Gi5+1qa5l9JuDKrA4YScNAv6Qktega4w4U+4ZBjzTXFvlUXlfU6zS+6GxzLSe8OvAYjNxoDwF1R0yuZb8jvzJx3cqH/9ztk" +
      "vPQTETCcTtsTihjpR/wVS1RsLsFJ/s3xqoX9QHkbKFEYBIt2fB1wAtWo4i4zW8jv1/U6ssnai6S9Ro6CfpYuo1+0a0J48KctCFiynZmI5Z5AA5Kx0CxX9rL7VglY/evuI7CIwEmjKuIxNUszAZsmOcNJPVBeOHD9+EjYJyGc5iAitvv7lI+P/mo5D982Q5n5fwIDAQAB";

  /**
   * Decrypts the specified cipher text using the specified public key string.
   *
   * @param cipherText the cipher text to decrypt
   * @param publicKeyString the public key string to use for decryption
   * @return the decrypted plain text
   *
   * @throws Exception if an error occurs while decrypting
   */
  public static String decrypt(String cipherText, String publicKeyString) throws Exception {
    // Convert the cipher text and public key string to bytes
    byte[] cipherTextBytes = Base64.getDecoder().decode(cipherText);
    byte[] publicKeyBytes = Base64.getDecoder().decode(publicKeyString);

    // Create a public key from the byte array
    X509EncodedKeySpec publicKeySpec = new X509EncodedKeySpec(publicKeyBytes);
    KeyFactory keyFactory = KeyFactory.getInstance("RSA");
    PublicKey publicKey = keyFactory.generatePublic(publicKeySpec);

    // Decrypt the cipher text
    Cipher cipher = Cipher.getInstance("RSA/ECB/PKCS1Padding");
    cipher.init(Cipher.DECRYPT_MODE, publicKey);
    byte[] plainTextBytes = cipher.doFinal(cipherTextBytes);

    // Return the decrypted plain text as a string
    return new String(plainTextBytes, "UTF-8");
  }

  public static void main(String[] args) throws Exception {
    // Example usage
    String cipherText = "W88pknTCSXS7IuBSATGHe1yLhM69mIz7VtnB0Co0z7V/uqZKWw5QPN31NYsf5rNtvIlzuL0ykl93cEzDtfe9EQ==";
    String plainText = decrypt(cipherText, PUBLIC_KEY_STRING);
    System.out.println(plainText);
  }
}

请注意，此示例代码仅适用于使用PKCS#1 padding算法的RSA密钥。如果使用其他算法，请相应地更改代码。另外，使用公钥进行解密通常不是一种很好的实践，因为这可能会暴露您的公钥并使系统容易受到中间人攻击。通常，RSA加密是使用私钥进行加密，使用公钥进行解密。