java SHA256 with RSA 代码

在Java中，SHA256是一种哈希函数用于数据摘要，而RSA是一种公钥加密算法。将SHA256的结果用作RSA加密的内容通常是这样的流程：

首先，你需要生成一个SHA256摘要（hash）：

import javax.crypto.Mac;
import javax.crypto.spec.SecretKeySpec;
import java.nio.charset.StandardCharsets;
import java.security.InvalidKeyException;
import java.security.NoSuchAlgorithmException;

public byte[] sha256(String input) {
    try {
        Mac sha256Hmac = Mac.getInstance("HmacSHA256");
        SecretKeySpec keySpec = new SecretKeySpec("your-secret-key".getBytes(StandardCharsets.UTF_8), "HmacSHA256");
        sha256Hmac.init(keySpec);
        return sha256Hmac.doFinal(input.getBytes(StandardCharsets.UTF_8));
    } catch (NoSuchAlgorithmException | InvalidKeyException e) {
        throw new RuntimeException("Error generating SHA-256", e);
    }
}

然后，你可以使用RSA加密这个摘要：

import java.math.BigInteger;
import java.security.KeyFactory;
import java.security.PrivateKey;
import java.security.spec.PKCS8EncodedKeySpec;
import javax.crypto.Cipher;

public String encryptWithRSA(byte[] hash, PrivateKey privateKey) {
    try {
        KeyFactory kf = KeyFactory.getInstance("RSA");
        PKCS8EncodedKeySpec privKeySpec = new PKCS8EncodedKeySpec(privateKey.getEncoded());
        PrivateKey privKey = kf.generatePrivate(privKeySpec);

        Cipher cipher = Cipher.getInstance("RSA/OAEPWithSHA-256AndMGF1Padding");
        cipher.init(Cipher.ENCRYPT_MODE, privKey);

        byte[] encryptedHash = cipher.doFinal(hash);
        return Base64.getEncoder().encodeToString(encryptedHash);
    } catch (Exception e) {
        throw new RuntimeException("Error encrypting with RSA", e);
    }
}

这里的`"your-secret-key"`需要替换为实际的密钥，`privateKey`是一个RSA私钥。