【Java加解密系列】- SM2加解密

上一篇部落格介紹了SM2演算法生成金鑰的過程，詳見-SM2生成金鑰。這篇部落格接著介紹SM2演算法如何用上篇部落格生成的金鑰進行加解密操作。

因為金鑰都是byte陣列，在進行加解密前，我們需要將金鑰轉換成BC庫的CipherParameters。程式碼如下：

/**
     * 私鑰轉換為 {@link ECPrivateKeyParameters}
     * @param key key
     * @return
     * @throws InvalidKeyException
     */
    public static ECPrivateKeyParameters privateKeyToParams(String algorithm, byte[] key) throws InvalidKeyException, InvalidKeySpecException, NoSuchAlgorithmException {
        Preconditions.checkNotNull(key, "key must be not null !");
        PrivateKey privateKey = generatePrivateKey(algorithm, key);
        return (ECPrivateKeyParameters) ECUtil.generatePrivateKeyParameter(privateKey);
    }

    /**
     * 生成私鑰
     * @param algorithm 演算法
     * @param key       key
     * @return
     */
    public static PrivateKey generatePrivateKey(String algorithm, byte[] key) throws NoSuchAlgorithmException, InvalidKeySpecException {
        Preconditions.checkNotNull(algorithm, "algorithm must be not null !");
        Preconditions.checkNotNull(key, "key must be not null !");
        KeySpec keySpec = new PKCS8EncodedKeySpec(key);
        algorithm = getAlgorithmAfterWith(algorithm);
        return getKeyFactory(algorithm).generatePrivate(keySpec);
    }

    /**
     * 公鑰轉換為 {@link ECPublicKeyParameters}
     * @param key key
     * @return
     * @throws InvalidKeyException
     */
    public static ECPublicKeyParameters publicKeyToParams(String algorithm, byte[] key) throws InvalidKeyException, InvalidKeySpecException, NoSuchAlgorithmException {
        Preconditions.checkNotNull(key, "key must be not null !");
        PublicKey publicKey = generatePublicKey(algorithm, key);
        return (ECPublicKeyParameters) ECUtil.generatePublicKeyParameter(publicKey);
    }

    /**
     * 生成公鑰
     * @param algorithm 演算法
     * @param key       key
     * @return
     */
    public static PublicKey generatePublicKey(String algorithm, byte[] key) throws NoSuchAlgorithmException, InvalidKeySpecException {
        Preconditions.checkNotNull(algorithm, "algorithm must be not null !");
        Preconditions.checkNotNull(key, "key must be not null !");
        KeySpec keySpec = new X509EncodedKeySpec(key);
        algorithm = getAlgorithmAfterWith(algorithm);
        return getKeyFactory(algorithm).generatePublic(keySpec);
    }

    /**
     * 獲取用於金鑰生成的演算法<br>
     * 獲取XXXwithXXX演算法的後半部分演算法，如果為ECDSA或SM2，返回演算法為EC
     * @param algorithm XXXwithXXX演算法
     * @return 演算法
     */
    private static String getAlgorithmAfterWith(String algorithm) {
        Preconditions.checkNotNull(algorithm, "algorithm must be not null !");
        int indexOfWith = StringUtils.lastIndexOfIgnoreCase(algorithm, "with");
        if (indexOfWith > 0) {
            algorithm = StringUtils.substring(algorithm, indexOfWith + "with".length());
        }
        if ("ECDSA".equalsIgnoreCase(algorithm) || "SM2".equalsIgnoreCase(algorithm)) {
            algorithm = "EC";
        }
        return algorithm;
    }

    /**
     * 獲取{@link KeyFactory}
     * @param algorithm 非對稱加密演算法
     * @return {@link KeyFactory}
     */
    private static KeyFactory getKeyFactory(String algorithm) throws NoSuchAlgorithmException {
        final Provider provider = new BouncyCastleProvider();
        return KeyFactory.getInstance(algorithm, provider);
    }

SM2操作主要有四類：加密、解密、簽名和驗籤。程式碼如下：

/**
     * 加密
     * @param data      資料
     * @param publicKey 公鑰
     * @return 加密之後的資料
     */
    public static byte[] encrypt(byte[] data, byte[] publicKey) throws Exception {
        CipherParameters pubKeyParameters = new ParametersWithRandom(publicKeyToParams("SM2", publicKey));
        SM2Engine engine = new SM2Engine(DIGEST);
        engine.init(true, pubKeyParameters);
        return engine.processBlock(data, 0, data.length);
    }

    /**
     * 解密
     * @param data       資料
     * @param privateKey 私鑰
     * @return 解密之後的資料
     */
    public static byte[] decrypt(byte[] data, byte[] privateKey) throws Exception {
        CipherParameters privateKeyParameters = privateKeyToParams("SM2", privateKey);
        SM2Engine engine = new SM2Engine(DIGEST);
        engine.init(false, privateKeyParameters);
        byte[] byteDate = engine.processBlock(data, 0, data.length);
        return byteDate;
    }

    /**
     * 簽名
     * @param data 資料
     * @return 簽名
     */
    public static byte[] sign(byte[] data, byte[] privateKey) throws Exception {
        SM2Signer signer = new SM2Signer();
        CipherParameters param = new ParametersWithRandom(privateKeyToParams("SM2", privateKey));
        signer.init(true, param);
        signer.update(data, 0, data.length);
        return signer.generateSignature();
    }

    /**
     * 用公鑰檢驗數字簽名的合法性
     * @param data      資料
     * @param sign      簽名
     * @param publicKey 公鑰
     * @return 是否驗證通過
     */
    public static boolean verify(byte[] data, byte[] sign, byte[] publicKey) throws Exception {
        SM2Signer signer = new SM2Signer();
        CipherParameters param = publicKeyToParams("SM2", publicKey);
        signer.init(false, param);
        signer.update(data, 0, data.length);
        return signer.verifySignature(sign);
    }

跑個測試用例試下：

public static void main(String[] args) throws Exception {
        KeyPair keyPair = generateSm2KeyPair();
        //明文
        String plaintext = "test";
        //加密
        String ciphertext = Base64Utils.encode(encrypt(plaintext.getBytes("utf-8"), keyPair.getPublic().getEncoded()));
        //生成簽名
        String signature = Base64Utils.encode(sign(plaintext.getBytes("utf-8"),keyPair.getPrivate().getEncoded()));
        System.out.println("ciphertext: " + ciphertext);
        System.out.println("signature: " + signature);
        //解密
        plaintext = new String(decrypt(Base64Utils.decode(ciphertext),keyPair.getPrivate().getEncoded()),"utf-8");
        //驗籤
        boolean result = verify(plaintext.getBytes("utf-8"),Base64Utils.decode(signature),keyPair.getPublic().getEncoded());
        System.out.println("plaintext: " + plaintext);
        System.out.println("verify result: " + result);
    }

輸出結果如下：

ciphertext: BFH0SXC1bX7OL1i5I4GO/Ck8Lak6gfzrsEzhrk4GY2cKZOug73ThLBYSjbtnpC5z30CJuKmaAf/W+jlviRr9PT1dcBWyrO599UUC4XWW8as4XHej8nE/Rlr9TP5+wP+4AWaub6o=
signature: MEYCIQC7OldJ7B8JvP51zw8P2DfieG5iAj5rWEybqZ3bPG8D5wIhAIVXlOmMxk0t4cNm0oQ0HYIzJZ5JShGIWuVwZLZ/t9mQ
plaintext: test
verify result: true

從結果可以看出，可以進行正常的加解密、生成簽名以及驗籤操作。