public static byte[] decrypt(byte[] cipher, PrivateKey privateKey) { try { Signature signature = Signature.getInstance("SHA256withRSA"); signature.initVerify(publicKey); signature.update(cipher); return signature.verify(cipher); } catch (Exception e) { e.printStackTrace(); } return null; } }这一代码中出现的Incompatible types. Found: 'boolean', required: 'byte[]'问题怎么解决

在这段代码中，`signature.verify(cipher)`返回的是`boolean`类型的值，而方法的返回类型是`byte[]`，这就导致了类型不兼容的错误。

要解决这个问题，你需要将方法的返回类型改为`boolean`，并且将方法名改为`verifySignature`，因为这个方法的作用是验证签名，而不是解密。

改造后的代码如下所示：

public static boolean verifySignature(byte[] cipher, PublicKey publicKey) {
    try {
        Signature signature = Signature.getInstance("SHA256withRSA");
        signature.initVerify(publicKey);
        signature.update(cipher);
        return signature.verify(cipher);
    } catch (Exception e) {
        e.printStackTrace();
    }
    return false;
}

注意，这里参数`publicKey`应该是验证签名所用的公钥，而不是解密所用的私钥，因为这里是验证签名的过程。

相关问题

import java.nio.charset.StandardCharsets; import java.security.KeyPair; import java.security.KeyPairGenerator; import java.security.NoSuchAlgorithmException; import java.security.PrivateKey; import java.security.PublicKey; import java.security.Signature; public class RSAEfficiency { private static PublicKey publicKey; private static PrivateKey privateKey; public static void main(String[] args) throws NoSuchAlgorithmException { String message = "Hello, World!"; byte[] messageBytes = message.getBytes(StandardCharsets.UTF_8); KeyPairGenerator keyPairGenerator = KeyPairGenerator.getInstance("RSA"); keyPairGenerator.initialize(2048); KeyPair keyPair = keyPairGenerator.generateKeyPair(); PublicKey publicKey = keyPair.getPublic(); PrivateKey privateKey = keyPair.getPrivate(); long startTime = System.nanoTime(); byte[] encryptedBytes = encrypt(messageBytes, publicKey); byte[] decryptedBytes = decrypt(encryptedBytes, privateKey); long endTime = System.nanoTime(); String decryptedMessage = new String(decryptedBytes, StandardCharsets.UTF_8); System.out.println("Original Message: " + message); System.out.println("Encrypted Message: " + new String(encryptedBytes, StandardCharsets.UTF_8)); System.out.println("Decrypted Message: " + decryptedMessage); System.out.println("Time taken: " + (endTime - startTime) + " ns"); } public static byte[] encrypt(byte[] message, PublicKey publicKey) { try { Signature signature = Signature.getInstance("SHA256withRSA"); signature.initSign(privateKey); signature.update(message); return signature.sign(); } catch (Exception e) { e.printStackTrace(); } return null; } public static boolean decrypt(byte[] cipher, PrivateKey privateKey) { try { Signature signature = Signature.getInstance("SHA256withRSA"); signature.initVerify(publicKey); signature.update(cipher); return signature.verify(cipher); } catch (Exception e) { e.printStackTrace(); } return null; } }这个代码有同样的问题怎么解决

这段代码和之前的代码一样存在类型不兼容的问题，因为`decrypt`方法的返回类型是`boolean`，而`return null;`语句返回了一个`null`值。

要解决这个问题，你需要将`return null;`语句改为`return false;`，因为返回的是`boolean`类型的值，而`false`表示解密失败，`true`表示解密成功。

改造后的代码如下所示：

public static boolean decrypt(byte[] cipher, PrivateKey privateKey) {
    try {
        Signature signature = Signature.getInstance("SHA256withRSA");
        signature.initVerify(publicKey);
        signature.update(cipher);
        return signature.verify(cipher);
    } catch (Exception e) {
        e.printStackTrace();
    }
    return false;
}

注意，这里参数`publicKey`应该是验证签名所用的公钥，而不是解密所用的私钥，因为这里是验证签名的过程。

给我一个SHA256withRSA的工具类

以下是一个使用Java编写的SHA256withRSA工具类的示例：

import java.security.Key;
import java.security.KeyFactory;
import java.security.PrivateKey;
import java.security.PublicKey;
import java.security.Signature;
import java.security.spec.PKCS8EncodedKeySpec;
import java.security.spec.X509EncodedKeySpec;

import javax.crypto.Cipher;

public class SHA256withRSAUtil {

    /**
     * 用私钥对信息生成数字签名
     * 
     * @param data 已加密数据
     * @param privateKey 私钥(BASE64编码)
     * 
     * @return
     * @throws Exception
     */
    public static String sign(byte[] data, String privateKey) throws Exception {
        byte[] keyBytes = Base64.decode(privateKey);
        PKCS8EncodedKeySpec pkcs8KeySpec = new PKCS8EncodedKeySpec(keyBytes);
        KeyFactory keyFactory = KeyFactory.getInstance("RSA");
        PrivateKey priKey = keyFactory.generatePrivate(pkcs8KeySpec);
        Signature signature = Signature.getInstance("SHA256withRSA");
        signature.initSign(priKey);
        signature.update(data);
        return Base64.encode(signature.sign());
    }

    /**
     * 校验数字签名
     * 
     * @param data 已加密数据
     * @param publicKey 公钥(BASE64编码)
     * @param sign 数字签名
     * 
     * @return
     * @throws Exception
     * 
     */
    public static boolean verify(byte[] data, String publicKey, String sign) throws Exception {
        byte[] keyBytes = Base64.decode(publicKey);
        X509EncodedKeySpec keySpec = new X509EncodedKeySpec(keyBytes);
        KeyFactory keyFactory = KeyFactory.getInstance("RSA");
        PublicKey pubKey = keyFactory.generatePublic(keySpec);
        Signature signature = Signature.getInstance("SHA256withRSA");
        signature.initVerify(pubKey);
        signature.update(data);
        return signature.verify(Base64.decode(sign));
    }

    /**
     * 私钥解密
     * 
     * @param encryptedData 已加密数据
     * @param privateKey 私钥(BASE64编码)
     * @return
     * @throws Exception
     */
    public static byte[] decryptByPrivateKey(byte[] encryptedData, String privateKey) throws Exception {
        byte[] keyBytes = Base64.decode(privateKey);
        PKCS8EncodedKeySpec pkcs8KeySpec = new PKCS8EncodedKeySpec(keyBytes);
        KeyFactory keyFactory = KeyFactory.getInstance("RSA");
        Key privateK = keyFactory.generatePrivate(pkcs8KeySpec);
        Cipher cipher = Cipher.getInstance("RSA");
        cipher.init(Cipher.DECRYPT_MODE, privateK);
        return cipher.doFinal(encryptedData);
    }

    /**
     * 公钥加密
     * 
     * @param data 源数据
     * @param publicKey 公钥(BASE64编码)
     * @return
     * @throws Exception
     */
    public static byte[] encryptByPublicKey(byte[] data, String publicKey) throws Exception {
        byte[] keyBytes = Base64.decode(publicKey);
        X509EncodedKeySpec x509KeySpec = new X509EncodedKeySpec(keyBytes);
        KeyFactory keyFactory = KeyFactory.getInstance("RSA");
        Key publicK = keyFactory.generatePublic(x509KeySpec);
        Cipher cipher = Cipher.getInstance("RSA");
        cipher.init(Cipher.ENCRYPT_MODE, publicK);
        return cipher.doFinal(data);
    }

}

注意：此工具类需要依赖Base64编码工具类，可以使用Java 8自带的Base64类或其他第三方库来实现。