java 实现 gcm

在Java中实现GCM加密可以使用Java Cryptography Extension (JCE)提供的javax.crypto.Cipher类，该类提供了GCM加密算法的实现。以下是一个简单的示例代码：

import javax.crypto.Cipher;
import javax.crypto.spec.GCMParameterSpec;
import javax.crypto.spec.SecretKeySpec;
import java.nio.charset.StandardCharsets;
import java.security.SecureRandom;
import java.util.Base64;

public class GcmExample {

    private static final int TAG_LENGTH_BITS = 128;
    private static final int IV_LENGTH_BYTES = 12;
    private static final int KEY_LENGTH_BYTES = 16;

    public static void main(String[] args) throws Exception {
        // 示例数据
        String keyStr = "000102030405060708090a0b0c0d0e0f";
        String ivStr = "10111213141516";
        String data = "Hello, world!";

        byte[] key = hexToBytes(keyStr);
        byte[] iv = hexToBytes(ivStr);

        // 加密
        byte[] encrypted = encrypt(data.getBytes(StandardCharsets.UTF_8), key, iv);
        System.out.println("Cipher text: " + Base64.getEncoder().encodeToString(encrypted));

        // 解密
        byte[] decrypted = decrypt(encrypted, key, iv);
        System.out.println("Decrypted data: " + new String(decrypted, StandardCharsets.UTF_8));
    }

    private static byte[] encrypt(byte[] data, byte[] key, byte[] iv) throws Exception {
        Cipher cipher = Cipher.getInstance("AES/GCM/NoPadding");
        SecretKeySpec keySpec = new SecretKeySpec(key, "AES");
        GCMParameterSpec gcmSpec = new GCMParameterSpec(TAG_LENGTH_BITS, iv);
        cipher.init(Cipher.ENCRYPT_MODE, keySpec, gcmSpec);
        byte[] encrypted = cipher.doFinal(data);
        byte[] tag = cipher.getParameters().getParameterSpec(GCMParameterSpec.class).getIV();
        byte[] result = new byte[encrypted.length + tag.length];
        System.arraycopy(encrypted, 0, result, 0, encrypted.length);
        System.arraycopy(tag, 0, result, encrypted.length, tag.length);
        return result;
    }

    private static byte[] decrypt(byte[] data, byte[] key, byte[] iv) throws Exception {
        Cipher cipher = Cipher.getInstance("AES/GCM/NoPadding");
        SecretKeySpec keySpec = new SecretKeySpec(key, "AES");
        GCMParameterSpec gcmSpec = new GCMParameterSpec(TAG_LENGTH_BITS, iv);
        cipher.init(Cipher.DECRYPT_MODE, keySpec, gcmSpec);
        int encryptedLength = data.length - IV_LENGTH_BYTES;
        byte[] encrypted = new byte[encryptedLength];
        System.arraycopy(data, 0, encrypted, 0, encryptedLength);
        byte[] tag = new byte[IV_LENGTH_BYTES];
        System.arraycopy(data, encryptedLength, tag, 0, IV_LENGTH_BYTES);
        cipher.updateAAD(tag);
        return cipher.doFinal(encrypted);
    }

    private static byte[] hexToBytes(String hex) {
        byte[] bytes = new byte[hex.length() / 2];
        for (int i = 0; i < bytes.length; i++) {
            bytes[i] = (byte) Integer.parseInt(hex.substring(i * 2, i * 2 + 2), 16);
        }
        return bytes;
    }

    private static byte[] generateRandomBytes(int length) {
        byte[] bytes = new byte[length];
        new SecureRandom().nextBytes(bytes);
        return bytes;
    }
}

在上面的示例中，我们使用JCE提供的javax.crypto.Cipher类实现了GCM加密和解密的功能。首先，我们定义了`encrypt`和`decrypt`两个函数，分别用于加密和解密。在加密函数中，我们首先使用`Cipher.getInstance`方法获取AES/GCM/NoPadding的Cipher实例，并使用`SecretKeySpec`和`GCMParameterSpec`分别设置密钥和初始化向量。然后，我们调用`Cipher.init`方法进行初始化，并使用`Cipher.doFinal`方法进行加密。最后，我们将加密结果和完整性校验值拼接在一起返回。

在解密函数中，我们首先使用`Cipher.getInstance`方法获取AES/GCM/NoPadding的Cipher实例，并使用`SecretKeySpec`和`GCMParameterSpec`分别设置密钥和初始化向量。然后，我们从输入数据中分离出加密结果和完整性校验值，并使用`Cipher.updateAAD`方法设置解密所需的完整性校验值。最后，我们调用`Cipher.doFinal`方法进行解密，并返回解密后的数据。

最后，我们使用示例数据进行加密和解密，并输出结果。