我找到了一个示例实现,它看起来像这样：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Security.Cryptography;

namespace OTP
{
    class Program
    {
        static void Main(string[] args)
        {
            System.Text.UTF8Encoding encoding = new System.Text.UTF8Encoding();
            byte[] secretKey = encoding.GetBytes("12345678901234567890");
            byte[] counter = encoding.GetBytes("1");
            Console.WriteLine(CalculateHotp(secretKey,counter));
            Console.ReadKey();
        }

        public static int CalculateHotp(byte[] key,byte[] counter)
        {
            var hmacsha1 = new HMACSHA1(key);
            byte[] hmac_result = hmacsha1.ComputeHash(counter);
            int offset = hmac_result[19] & 0x0f;
            int bin_code = (hmac_result[offset] & 0x7f) << 24
                           | (hmac_result[offset + 1] & 0xff) << 16
                           | (hmac_result[offset + 2] & 0xff) << 8
                           | (hmac_result[offset + 3] & 0xff);
            int hotp = bin_code % 1000000;
            return hotp;
        }
    }
}

问题是电话：

byte[] hmac_result = hmacsha1.ComputeHash(counter);

不返回预期的结果,因此返回的OTP将是错误的.阅读RFC4226附录D(http://tools.ietf.org/html/rfc4226#appendix-D),有一些测试值要使用,结果与它们不匹配：

From the RFC 4226,Appendix D:
The following test data uses the ASCII string
 "12345678901234567890" for the secret:

  Secret = 0x3132333435363738393031323334353637383930

  Table 1 details for each count,the intermediate HMAC value.

Count    Hexadecimal HMAC-SHA-1(secret,count)
0        cc93cf18508d94934c64b65d8ba7667fb7cde4b0
1        75a48a19d4cbe100644e8ac1397eea747a2d33ab
2        0bacb7fa082fef30782211938bc1c5e70416ff44
3        66c28227d03a2d5529262ff016a1e6ef76557ece
4        a904c900a64b35909874b33e61c5938a8e15ed1c
<snip>

Table 2 details for each count the truncated values (both in
hexadecimal and decimal) and then the HOTP value.

                  Truncated
Count    Hexadecimal    Decimal        HOTP
0        4c93cf18       1284755224     755224
1        41397eea       1094287082     287082
2         82fef30        137359152     359152
3        66ef7655       1726969429     969429
4        61c5938a       1640338314     338314
<snip>

由于我在上面的示例中使用“12345678901234567890”作为键,使用“1”作为计数器,我希望ComputeHash()的结果为：
75a48a19d4cbe100644e8ac1397eea747a2d33ab
和OTP是：
287082

但是我得到了OTP：
906627

我真的无法看到我在这里做错了什么,有没有人使用HMACSHA1类在C#中成功实现了基于计数器的OTP？