什么变量在特定的固定时间间隔内保持真实？

Question

我有一个很酷的方法来生成一个6位数的散列用于电话验证。

该代码永远不会被存储，而是通过操纵该特定手机加上一些其他变量（包括导致在小时结束时发布的代码在用户有机会使用它们之前到期的发布时间）来计算的。

我怎么能拿到一定的时间间隔内保持不变，包括它使代码后自动失效时间变量？

public string getTimeVariable(long minutes) 
{ 
    var now=DateTime.Now; 
    //Some imprementation I cant think of.... 
} 

public bool verifyVariable(string variable) 
{ 
    //Some other implementation to return true if specified minutes haven't elapsed since variable was issued 
} 

Answer 1

考虑一下这段代码，它只是简单地开放以查看哪些代码在上一段时间内是有效的。代码现在每秒更改一次。您可以更改期限大小以及过去仍被视为有效的期数。

顺便说一句 - 你有什么酷的方法是什么呢？

using System; 
using System.Text; 
using System.Threading; 

public class Test { 

private static long secret = 0xdeadbeef; 
private static int digits = 6; 
private static int period_size_in_seconds = 1; 

public string phonenumber; 
public int validperiods; 

private string reference(long delta) { 
    // get current minute (UTC) 
    long now = DateTime.Now.ToUniversalTime().ToFileTimeUtc(); 
    now /= (period_size_in_seconds * 10000000); 
    // factor in phone number 
    var inputBytes = Encoding.ASCII.GetBytes(phonenumber); 
    long mux = 0; 
    foreach(byte elem in inputBytes) { 
    mux ^= elem; 
    mux <<= 1; 
    } 
    // limit number of digits 
    long mod = Convert.ToInt64(Math.Pow(10, digits)) - 1; // how many digits? 
    // apply time shift for validations 
    now -= delta; 
    // and play a little bit 
    now *= mux; // factor in phone number 
    now ^= secret; // play a bit 
    now >>= 1; // with the number 
    if (0 != (now & 0x1)) { // to make the code 
    now >>= 1; // read about LFSR to learn more 
    now ^= secret; // less deterministic 
    } 
    now = Math.Abs(now); 
    now %= mod; // keep the output in range 
    return now.ToString().PadLeft(digits, '0'); 
} 

public string getTimeVariable() { 
    return reference(0); 
} 

public bool verifyVariable(string variable) { 
    for (int i = 0; i < validperiods; i++) { 
    if (variable == reference(i)) { 
    return true; 
    } 
    } 
    return false; 
} 

public void test() { 
    phonenumber = "+48602171819"; 
    validperiods = 900; 
    string code = getTimeVariable(); 

    if (verifyVariable(getTimeVariable())) 
    System.Console.Write("OK1"); 

    if (verifyVariable(code)) 
    System.Console.Write(" OK2"); 

    Thread.Sleep(2*1000*period_size_in_seconds); 

    if (verifyVariable(code)) { 
    System.Console.WriteLine(" OK3"); 
    } 

    System.Console.WriteLine(code); 
} 

public static void Main() { 
    (new Test()).test(); 
} 
}