Google Authenticator 的java代码

以下是 Google Authenticator 的 Java 代码：

import java.security.InvalidKeyException;
import java.security.NoSuchAlgorithmException;
import java.security.SecureRandom;
import java.util.Arrays;
import javax.crypto.Mac;
import javax.crypto.spec.SecretKeySpec;
import org.apache.commons.codec.binary.Base32;

public class GoogleAuthenticator {
  // These fields are required for generating codes.
  private static final int SECRET_SIZE = 10;
  private static final int INTERVAL = 30;

  // These fields are required for validating codes.
  private static final int WINDOW_SIZE = 3;

  private static final Base32 base32 = new Base32();

  /**
   * Generate a new secret key.
   */
  public static String generateSecretKey() {
    SecureRandom random = new SecureRandom();
    byte[] bytes = new byte[SECRET_SIZE];
    random.nextBytes(bytes);
    return base32.encodeToString(bytes);
  }

  /**
   * Generate a code for the given secret key and time.
   */
  public static int generateCode(String secret, long time) throws NoSuchAlgorithmException, InvalidKeyException {
    byte[] key = base32.decode(secret);
    byte[] data = new byte[8];
    long value = time / INTERVAL;
    for (int i = 7; i >= 0; i--) {
      data[i] = (byte) (value & 0xff);
      value >>= 8;
    }
    SecretKeySpec signingKey = new SecretKeySpec(key, "HmacSHA1");
    Mac mac = Mac.getInstance("HmacSHA1");
    mac.init(signingKey);
    byte[] hash = mac.doFinal(data);
    int offset = hash[hash.length - 1] & 0xf;
    int truncatedHash = 0;
    for (int i = 0; i < 4; i++) {
      truncatedHash <<= 8;
      truncatedHash |= (hash[offset + i] & 0xff);
    }
    truncatedHash &= 0x7fffffff;
    truncatedHash %= 1000000;
    return truncatedHash;
  }

  /**
   * Validate a code for the given secret key and time.
   */
  public static boolean validateCode(String secret, int code, long time) throws NoSuchAlgorithmException, InvalidKeyException {
    for (int i = -WINDOW_SIZE; i <= WINDOW_SIZE; i++) {
      long t = time + i * INTERVAL;
      int c = generateCode(secret, t);
      if (c == code) {
        return true;
      }
    }
    return false;
  }

  public static void main(String[] args) throws Exception {
    // Generate a new secret key.
    String secret = generateSecretKey();
    System.out.println("Secret key: " + secret);

    // Get the current time.
    long time = System.currentTimeMillis();

    // Generate a code for the current time.
    int code = generateCode(secret, time);
    System.out.println("Code: " + code);

    // Validate the code for the current time.
    boolean valid = validateCode(secret, code, time);
    System.out.println("Valid: " + valid);
  }
}

这个 Java 类包含了三个方法：

- `generateSecretKey()`：生成一个新的密钥。
- `generateCode(secret, time)`：使用给定的密钥和时间生成一个验证码。
- `validateCode(secret, code, time)`：使用给定的密钥、验证码和时间验证代码是否有效。

这三个方法都使用了 Google Authenticator 协议，可以用于生成和验证 Google Authenticator 代码。