SHA256withRSA签名与验签代码示例

以下是SHA256withRSA签名与验签的Java代码示例：

**签名代码：**

import java.security.*;
import java.util.Base64;

public class RSASignatureExample {

    public static void main(String[] args) throws Exception {
        String message = "This is a message to be signed.";

        // Generate key pair
        KeyPairGenerator keyGen = KeyPairGenerator.getInstance("RSA");
        keyGen.initialize(2048);
        KeyPair keyPair = keyGen.generateKeyPair();

        // Create a signature object
        Signature signature = Signature.getInstance("SHA256withRSA");

        // Initialize the signature object with the private key
        PrivateKey privateKey = keyPair.getPrivate();
        signature.initSign(privateKey);

        // Update the signature object with the message
        signature.update(message.getBytes());

        // Sign the message
        byte[] signatureBytes = signature.sign();

        // Print the signature in Base64 encoding
        System.out.println("Signature: " + Base64.getEncoder().encodeToString(signatureBytes));
    }
}

**验签代码：**

import java.security.*;
import java.util.Base64;

public class RSASignatureExample {

    public static void main(String[] args) throws Exception {
        String message = "This is a message to be signed.";
        String signatureString = "PLl6yBb6IhOv0Jd3k1y/YlR9a3UOx0WJQy6RbbS/3W8mQ2ztcL5x+JShHl6O8gTlJn4wtNQ7Ggz0ZiPwq9SInQf/9d4eG4qSkZCzVgP9U9bQY7jwFVhWXfzqU6l5K8SxyA2pBw+PQs0N2dJQ2Xk9V3tXZP5h+UcMXwLQe/3K7uh2M=";

        // Generate key pair
        KeyPairGenerator keyGen = KeyPairGenerator.getInstance("RSA");
        keyGen.initialize(2048);
        KeyPair keyPair = keyGen.generateKeyPair();

        // Create a signature object
        Signature signature = Signature.getInstance("SHA256withRSA");

        // Initialize the signature object with the public key
        PublicKey publicKey = keyPair.getPublic();
        signature.initVerify(publicKey);

        // Update the signature object with the message
        signature.update(message.getBytes());

        // Verify the signature
        boolean verified = signature.verify(Base64.getDecoder().decode(signatureString));

        // Print the verification result
        System.out.println("Signature verified: " + verified);
    }
}

以上代码示例中，我们使用SHA256withRSA算法对一个字符串进行签名和验签。在签名时，我们首先生成了一个RSA密钥对，然后使用私钥对消息进行签名，并打印出Base64编码的签名结果。在验签时，我们使用同样的RSA密钥对和签名算法，使用公钥初始化签名对象，并使用该对象对消息进行验证，最终打印验证结果。需要注意的是，验签时需要将签名结果从Base64编码中解码。