【Java】Google身份验证服务端实现

import org.apache.commons.codec.binary.Base32;
import org.apache.commons.codec.binary.Base64;
import javax.crypto.Mac;
import javax.crypto.spec.SecretKeySpec;
import java.security.InvalidKeyException;
import java.security.NoSuchAlgorithmException;
import java.security.SecureRandom;
 
/**
 * google身份验证器，java服务端实现
 */
public class GoogleAuthenticator {
 
	// 生成的key长度( Generate secret key length)
	public static final int SECRET_SIZE = 10;
 
	public static final String SEED = "g8GjEvTbW5oVSV7avL47357438reyhreyuryetredLDVKs2m0QN7vxRs2im5MDaNCWGmcD2rvcZx";
	// Java实现随机数算法
	public static final String RANDOM_NUMBER_ALGORITHM = "SHA1PRNG";
	// 最多可偏移的时间
	int window_size = 3; // default 3 - max 17
 
	/**
	 * set the windows size. This is an integer value representing the number of
	 * 30 second windows we allow The bigger the window, the more tolerant of
	 * clock skew we are.
	 * 
	 * @param s
	 *            window size - must be >=1 and = 1 && s >>= 8) {
			data[i] = (byte) value;
		}
		SecretKeySpec signKey = new SecretKeySpec(key, "HmacSHA1");
		Mac mac = Mac.getInstance("HmacSHA1");
		mac.init(signKey);
		byte[] hash = mac.doFinal(data);
		int offset = hash[20 - 1] & 0xF;
		// We're using a long because Java hasn't got unsigned int.
		long truncatedHash = 0;
		for (int i = 0; i < 4; ++i) {
			truncatedHash