一、HOTP
HOTP 算法,全称是“An HMAC-Based One-Time Password Algorithm”,是一种基于事件计数的一次性密码生成算法,详细的算法介绍可以查看 RFC 4226。其实算法本身非常简单,算法本身可以用两条简短的表达式描述:
HOTP(K,C) = Truncate(HMAC-SHA-1(K,C))
PWD(K,C,digit) = HOTP(K,C) mod 10^Digit
二、TOTP
TOTP 算法,全称是 TOTP: Time-Based One-Time Password Algorithm,其基于 HOTP 算法实现,核心是将移动因子从 HOTP 中的事件计数改为时间差。完整的 TOTP 算法的说明可以查看 RFC 6238,其公式描述也非常简单:
TOTP = HOTP(K, T) // T is an integer
and represents the number of time steps between the initial counter
time T0 and the current Unix time
More specifically, T = (Current Unix time - T0) / X, where the
default floor function is used in the computation.
参考《/a/1190000008394200》
这篇文章已经介绍清楚动态密码的原理,本文仅在理论的基础上使用Java实现。
三、TOTP具体Java实现
子服务端:启用不含verifyTOTP*()验证方法的TOTP,使用子服务端的账户和密码加密,向验证服务端发送动态口令。
验证服务端:验证子服务端的口令,根据子服务端标识信息,使用其账户和密码加密得到口令,比对口令是否一致即可。
前提:因为使用时间作为动态因子加密口令,子服务端的时间应和验证服务端的时间一致,比如使用同一个授时服务器授时。
推荐使用柔性口令验证,使用柔性验证时请设置时间回溯参数,避免因口令在网络中传输消耗时间,或者服务端时间误差导致口令失效。
/**
*
ClassName: TOTP
*
Description: TOTP = HOTP(K, T) // T is an integer
* and represents the number of time steps between the initial counter
* time T0 and the current Unix time
*
* More specifically, T = (Current Unix time - T0) / X, where the
* default floor function is used in the computation.
*
* @author wangqian
* @date -04-03 11:44
*/
public class TOTP {
public static void main(String[] args) {
try {
for (int j = 0; j < 10; j++) {
String totp = generateMyTOTP("account01", "12345");
System.out.println(String.format("加密后: %s", totp));
Thread.sleep(1000);
}
} catch (final Exception e) {
e.printStackTrace();
}
}
/**
* 共享密钥
*/
private static final String SECRET_KEY = "ga35sdia43dhqj6k3f0la";
/**
* 时间步长 单位:毫秒 作为口令变化的时间周期
*/
private static final long STEP = 30000;
/**
* 转码位数 [1-8]
*/
private static final int CODE_DIGITS = 8;
/**
* 初始化时间
*/
private static final long INITIAL_TIME = 0;
/**
* 柔性时间回溯
*/
private static final long FLEXIBILIT_TIME = 5000;
/**
* 数子量级
*/
private static final int[] DIGITS_POWER = {1, 10, 100, 1000, 10000, 100000, 1000000, 10000000, 100000000};
private TOTP() {
}
/**
* 生成一次性密码
*
* @param code 账户
* @param pass 密码
* @return String
*/
public static String generateMyTOTP(String code, String pass) {
if (EmptyUtil.isEmpty(code) || EmptyUtil.isEmpty(pass)) {
throw new RuntimeException("账户密码不许为空");
}
long now = new Date().getTime();
String time = Long.toHexString(timeFactor(now)).toUpperCase();
return generateTOTP(code + pass + SECRET_KEY, time);
}
/**
* 刚性口令验证
*
* @param code 账户
* @param pass 密码
* @param totp 待验证的口令
* @return boolean
*/
public static boolean verifyTOTPRigidity(String code, String pass, String totp) {
return generateMyTOTP(code, pass).equals(totp);
}
/**
* 柔性口令验证
*
* @param code 账户
* @param pass 密码
* @param totp 待验证的口令
* @return boolean
*/
public static boolean verifyTOTPFlexibility(String code, String pass, String totp) {
long now = new Date().getTime();
String time = Long.toHexString(timeFactor(now)).toUpperCase();
String tempTotp = generateTOTP(code + pass + SECRET_KEY, time);
if (tempTotp.equals(totp)) {
return true;
}
String time2 = Long.toHexString(timeFactor(now - FLEXIBILIT_TIME)).toUpperCase();
String tempTotp2 = generateTOTP(code + pass + SECRET_KEY, time2);
return tempTotp2.equals(totp);
}
/**
* 获取动态因子
*
* @param targetTime 指定时间
* @return long
*/
private static long timeFactor(long targetTime) {
return (targetTime - INITIAL_TIME) / STEP;
}
/**
* 哈希加密
*
* @param crypto 加密算法
* @param keyBytes 密钥数组
* @param text 加密内容
* @return byte[]
*/
private static byte[] hmac_sha(String crypto, byte[] keyBytes, byte[] text) {
try {
Mac hmac;
hmac = Mac.getInstance(crypto);
SecretKeySpec macKey = new SecretKeySpec(keyBytes, "AES");
hmac.init(macKey);
return hmac.doFinal(text);
} catch (GeneralSecurityException gse) {
throw new UndeclaredThrowableException(gse);
}
}
private static byte[] hexStr2Bytes(String hex) {
byte[] bArray = new BigInteger("10" + hex, 16).toByteArray();
byte[] ret = new byte[bArray.length - 1];
System.arraycopy(bArray, 1, ret, 0, ret.length);
return ret;
}
private static String generateTOTP(String key, String time) {
return generateTOTP(key, time, "HmacSHA1");
}
private static String generateTOTP256(String key, String time) {
return generateTOTP(key, time, "HmacSHA256");
}
private static String generateTOTP512(String key, String time) {
return generateTOTP(key, time, "HmacSHA512");
}
private static String generateTOTP(String key, String time, String crypto) {
StringBuilder timeBuilder = new StringBuilder(time);
while (timeBuilder.length() < 16)
timeBuilder.insert(0, "0");
time = timeBuilder.toString();
byte[] msg = hexStr2Bytes(time);
byte[] k = key.getBytes();
byte[] hash = hmac_sha(crypto, k, msg);
return truncate(hash);
}
/**
* 截断函数
*
* @param target 20字节的字符串
* @return String
*/
private static String truncate(byte[] target) {
StringBuilder result;
int offset = target[target.length - 1] & 0xf;
int binary = ((target[offset] & 0x7f) << 24)
| ((target[offset + 1] & 0xff) << 16)
| ((target[offset + 2] & 0xff) << 8) | (target[offset + 3] & 0xff);
int otp = binary % DIGITS_POWER[CODE_DIGITS];
result = new StringBuilder(Integer.toString(otp));
while (result.length() < CODE_DIGITS) {
result.insert(0, "0");
}
return result.toString();
}
}