对文本或文件进行数字签名。

Kotlin 代码：

代码区域可编辑，点击右上角可运行，运行结果在代码底部。

网页链接

公钥、私钥和签名内容均以 Base64 编码为字符串。

SignatureToolbox 中的方法：

• createKeyPair()
  新建一对公钥和私钥并返回。
• signText()/signFile()
  使用私钥，对文本/文件进行数字签名，并返回签名内容。
• verifyTextSign()/verifyFileSign()
  使用公钥和签名，验证文本/文件的内容是否正确并返回结果。

密钥算法是 DSA ，长度 2048，签名算法是 SHA256withDSA。编辑代码中的这些常量可以变更算法。

@tasy5kg，以下是将给定的Kotlin代码转换为Java代码后的结果：

import java.io.BufferedInputStream;
import java.io.FileInputStream;
import java.security.*;
import java.security.spec.PKCS8EncodedKeySpec;
import java.security.spec.X509EncodedKeySpec;
import java.util.Base64;

public class Main {
    private static final String KEY_PAIR_GENERATOR_ALGORITHM = "DSA";
    private static final int KEY_SIZE = 2048;
    private static final String SIGNATURE_ALGORITHM = "SHA256withDSA";
    private static final int FILE_BUFFER_SIZE = 4096;

    public static void main(String[] args) {
        SignatureToolbox signatureToolbox = SignatureToolbox.getInstance();
        SignatureToolbox.KeyPairBase64 keyPair = signatureToolbox.createKeyPair();
        String publicKey = keyPair.getPublicKey();
        String privateKey = keyPair.getPrivateKey();
        System.out.println("New key pair created.");
        System.out.println("Public key: " + publicKey);
        System.out.println("Private key: " + privateKey);
        String textToSign = "这里是要被数字签名的文字。";
        System.out.println("Text to sign: " + textToSign);
        String signature = signatureToolbox.signText(textToSign, privateKey);
        System.out.println("Signature: " + signature);
        System.out.println("Verify signature: " + signatureToolbox.verifyTextSign(textToSign, publicKey, signature));
    }

    static class SignatureToolbox {
        private static final String KEY_PAIR_GENERATOR_ALGORITHM = Main.KEY_PAIR_GENERATOR_ALGORITHM;
        private static final int KEY_SIZE = Main.KEY_SIZE;
        private static final String SIGNATURE_ALGORITHM = Main.SIGNATURE_ALGORITHM;
        private static final int FILE_BUFFER_SIZE = Main.FILE_BUFFER_SIZE;

        private static SignatureToolbox instance;

        private SignatureToolbox() {
        }

        public static SignatureToolbox getInstance() {
            if (instance == null) {
                instance = new SignatureToolbox();
            }
            return instance;
        }

        public KeyPairBase64 createKeyPair() throws NoSuchAlgorithmException {
            KeyPairGenerator keyPairGenerator = KeyPairGenerator.getInstance(KEY_PAIR_GENERATOR_ALGORITHM);
            keyPairGenerator.initialize(KEY_SIZE);
            KeyPair keyPair = keyPairGenerator.generateKeyPair();
            return new KeyPairBase64(keyPair);
        }

        public String signText(String text, String privateKeyBase64) throws Exception {
            Signature signature = Signature.getInstance(SIGNATURE_ALGORITHM);
            signature.initSign(base64ToPrivateKey(privateKeyBase64));
            signature.update(text.getBytes());
            byte[] signedBytes = signature.sign();
            return toBase64(signedBytes);
        }

        public String signFile(String filePath, String privateKeyBase64) throws Exception {
            Signature signature = Signature.getInstance(SIGNATURE_ALGORITHM);
            signature.initSign(base64ToPrivateKey(privateKeyBase64));
            BufferedInputStream bufferedInputStream = new BufferedInputStream(new FileInputStream(filePath));
            byte[] buffer = new byte[FILE_BUFFER_SIZE];
            int len;
            while ((len = bufferedInputStream.read(buffer)) >= 0) {
                signature.update(buffer, 0, len);
            }
            bufferedInputStream.close();
            byte[] signedBytes = signature.sign();
            return toBase64(signedBytes);
        }

        public boolean verifyTextSign(String text, String publicKeyBase64, String signatureBase64) throws Exception {
            Signature signature = Signature.getInstance(SIGNATURE_ALGORITHM);
            signature.initVerify(base64ToPublicKey(publicKeyBase64));
            signature.update(text.getBytes());
            byte[] signatureBytes = base64ToByteArray(signatureBase64);
            return signature.verify(signatureBytes);
        }

        public boolean verifyFileSign(String filePath, String publicKeyBase64,