一、Google Authenticator 基本概念
Google Authenticator是谷歌推出的一款动态口令工具，旨在解决大家Google账户遭到恶意攻击的问题，在手机端生成动态口令后，在Google相关的服务登陆中除了用正常用户名和密码外，需要输入一次动态口令才能验证成功，此举是为了保护用户的信息安全。
谷歌验证（Google Authenticator）通过两个验证步骤，在登录时为用户的谷歌帐号提供一层额外的安全保护。使用谷歌验证可以直接在用户的设备上生成动态密码，无需网络连接。其基本步骤如下：
- 使用google authenticator PAM插件为登录账号生成动态验证码。
- 手机安装Google身份验证器，通过此工具扫描上一步生成的二维码图形，获取动态验证码。
当用户在Google帐号中启用“两步验证”功能后，就可以使用Google Authenticator来防止陌生人通过盗取的密码访问用户的帐户。通过两步验证流程登录时，用户需要同时使用密码和通过手机产生的动态密码来验证用户的身份。也就是说，即使可能的入侵者窃取或猜出了用户的密码，也会因不能使用用户的手机而无法登录帐户。
更多原理可以查看阅读“详解Google Authenticator工作原理”。
二、.NET 使用 Google Authenticator
第一步，通过 Nuget 下载 Google Authenticator 安装包
第二步，例如我们要实现这样的功能：手机扫描 PC 生成的二维码，绑定用户信息后，后续使用手机生成的验证码输入到 PC 端进行校验。我们通过编程生成一个二维码如下图所示：
第三步：安装 Google Authenticator APP，安卓版下载、IOS下载（注意：安卓版本下载需翻墙）。安装成功后，扫描上图的二维码添加如下：
第四步：输入生成的验证码，在 PC 端输入口令后，展示校验通过（注意：口令有效时间为30秒）。
Google Authenticator 在 PC 端生成二维码、手机上生成验证码、 PC 端校验验证码，这些过程无需网络，只需要保证 PC 时间和手机时间正确一致即可。
Google Authenticator 工具类代码如下（引用自 https://www.cnblogs.com/denuk/p/11608510.html）：
1 public class GoogleAuthenticator
2 {
3 private readonly static DateTime _epoch = new DateTime(1970, 1, 1, 0, 0, 0, DateTimeKind.Utc);
4 private TimeSpan DefaultClockDriftTolerance { get; set; }
5
6 public GoogleAuthenticator()
7 {
8 DefaultClockDriftTolerance = TimeSpan.FromMinutes(5);
9 }
10
11 /// <summary>
12 /// Generate a setup code for a Google Authenticator user to scan
13 /// </summary>
14 /// <param name="issuer">Issuer ID (the name of the system, i.e. 'MyApp'), can be omitted but not recommended https://github.com/google/google-authenticator/wiki/Key-Uri-Format </param>
15 /// <param name="accountTitleNoSpaces">Account Title (no spaces)</param>
16 /// <param name="accountSecretKey">Account Secret Key</param>
17 /// <param name="QRPixelsPerModule">Number of pixels per QR Module (2 pixels give ~ 100x100px QRCode)</param>
18 /// <returns>SetupCode object</returns>
19 public SetupCode GenerateSetupCode(string issuer, string accountTitleNoSpaces, string accountSecretKey, int QRPixelsPerModule)
20 {
21 byte[] key = Encoding.UTF8.GetBytes(accountSecretKey);
22 return GenerateSetupCode(issuer, accountTitleNoSpaces, key, QRPixelsPerModule);
23 }
24
25 /// <summary>
26 /// Generate a setup code for a Google Authenticator user to scan
27 /// </summary>
28 /// <param name="issuer">Issuer ID (the name of the system, i.e. 'MyApp'), can be omitted but not recommended https://github.com/google/google-authenticator/wiki/Key-Uri-Format </param>
29 /// <param name="accountTitleNoSpaces">Account Title (no spaces)</param>
30 /// <param name="accountSecretKey">Account Secret Key as byte[]</param>
31 /// <param name="QRPixelsPerModule">Number of pixels per QR Module (2 = ~120x120px QRCode)</param>
32 /// <returns>SetupCode object</returns>
33 public SetupCode GenerateSetupCode(string issuer, string accountTitleNoSpaces, byte[] accountSecretKey, int QRPixelsPerModule)
34 {
35 if (accountTitleNoSpaces == null) { throw new NullReferenceException("Account Title is null"); }
36 accountTitleNoSpaces = RemoveWhitespace(accountTitleNoSpaces);
37 string encodedSecretKey = Base32Encoding.ToString(accountSecretKey);
38 string provisionUrl = null;
39 provisionUrl = String.Format("otpauth://totp/{2}:{0}?secret={1}&issuer={2}", accountTitleNoSpaces, encodedSecretKey.Replace("=", ""), UrlEncode(issuer));
40
41
42
43 using (QRCodeGenerator qrGenerator = new QRCodeGenerator())
44 using (QRCodeData qrCodeData = qrGenerator.CreateQrCode(provisionUrl, QRCodeGenerator.ECCLevel.M))
45 using (QRCode qrCode = new QRCode(qrCodeData))
46 using (Bitmap qrCodeImage = qrCode.GetGraphic(QRPixelsPerModule))
47 using (MemoryStream ms = new MemoryStream())
48 {
49 qrCodeImage.Save(ms, System.Drawing.Imaging.ImageFormat.Png);
50
51 return new SetupCode(accountTitleNoSpaces, encodedSecretKey, String.Format("data:image/png;base64,{0}", Convert.ToBase64String(ms.ToArray())));
52 }
53
54 }
55
56 private static string RemoveWhitespace(string str)
57 {
58 return new string(str.Where(c => !Char.IsWhiteSpace(c)).ToArray());
59 }
60
61 private string UrlEncode(string value)
62 {
63 StringBuilder result = new StringBuilder();
64 string validChars = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789-_.~";
65
66 foreach (char symbol in value)
67 {
68 if (validChars.IndexOf(symbol) != -1)
69 {
70 result.Append(symbol);
71 }
72 else
73 {
74 result.Append('%' + String.Format("{0:X2}", (int)symbol));
75 }
76 }
77
78 return result.ToString().Replace(" ", "%20");
79 }
80
81 public string GeneratePINAtInterval(string accountSecretKey, long counter, int digits = 6)
82 {
83 return GenerateHashedCode(accountSecretKey, counter, digits);
84 }
85
86 internal string GenerateHashedCode(string secret, long iterationNumber, int digits = 6)
87 {
88 byte[] key = Encoding.UTF8.GetBytes(secret);
89 return GenerateHashedCode(key, iterationNumber, digits);
90 }
91
92 internal string GenerateHashedCode(byte[] key, long iterationNumber, int digits = 6)
93 {
94 byte[] counter = BitConverter.GetBytes(iterationNumber);
95
96 if (BitConverter.IsLittleEndian)
97 {
98 Array.Reverse(counter);
99 }
100
101 HMACSHA1 hmac = new HMACSHA1(key);
102
103 byte[] hash = hmac.ComputeHash(counter);
104
105 int offset = hash[hash.Length - 1] & 0xf;
106
107 // Convert the 4 bytes into an integer, ignoring the sign.
108 int binary =
109 ((hash[offset] & 0x7f) << 24)
110 | (hash[offset + 1] << 16)
111 | (hash[offset + 2] << 8)
112 | (hash[offset + 3]);
113
114 int password = binary % (int)Math.Pow(10, digits);
115 return password.ToString(new string('0', digits));
116 }
117
118 private long GetCurrentCounter()
119 {
120 return GetCurrentCounter(DateTime.UtcNow, _epoch, 30);
121 }
122
123 private long GetCurrentCounter(DateTime now, DateTime epoch, int timeStep)
124 {
125 return (long)(now - epoch).TotalSeconds / timeStep;
126 }
127
128 public bool ValidateTwoFactorPIN(string accountSecretKey, string twoFactorCodeFromClient)
129 {
130 return ValidateTwoFactorPIN(accountSecretKey, twoFactorCodeFromClient, DefaultClockDriftTolerance);
131 }
132
133 public bool ValidateTwoFactorPIN(string accountSecretKey, string twoFactorCodeFromClient, TimeSpan timeTolerance)
134 {
135 var codes = GetCurrentPINs(accountSecretKey, timeTolerance);
136 return codes.Any(c => c == twoFactorCodeFromClient);
137 }
138
139 public string[] GetCurrentPINs(string accountSecretKey, TimeSpan timeTolerance)
140 {
141 List<string> codes = new List<string>();
142 long iterationCounter = GetCurrentCounter();
143 int iterationOffset = 0;
144
145 if (timeTolerance.TotalSeconds > 30)
146 {
147 iterationOffset = Convert.ToInt32(timeTolerance.TotalSeconds / 30.00);
148 }
149
150 long iterationStart = iterationCounter - iterationOffset;
151 long iterationEnd = iterationCounter + iterationOffset;
152
153 for (long counter = iterationStart; counter <= iterationEnd; counter++)
154 {
155 codes.Add(GeneratePINAtInterval(accountSecretKey, counter));
156 }
157
158 return codes.ToArray();
159 }
160
161 /// <summary>
162 /// Writes a string into a bitmap
163 /// </summary>
164 /// <param name="qrCodeSetupImageUrl"></param>
165 /// <returns></returns>
166 public static Image GetQRCodeImage(string qrCodeSetupImageUrl)
167 {
168 // data:image/png;base64,
169 qrCodeSetupImageUrl = qrCodeSetupImageUrl.Replace("data:image/png;base64,", "");
170 Image img = null;
171 byte[] buffer = Convert.FromBase64String(qrCodeSetupImageUrl);
172 using (MemoryStream ms = new MemoryStream(buffer))
173 {
174 img = Image.FromStream(ms);
175 }
176 return img;
177 }
178 }
179
180 public class Base32Encoding
181 {
182 /// <summary>
183 /// Base32 encoded string to byte[]
184 /// </summary>
185 /// <param name="input">Base32 encoded string</param>
186 /// <returns>byte[]</returns>
187 public static byte[] ToBytes(string input)
188 {
189 if (string.IsNullOrEmpty(input))
190 {
191 throw new ArgumentNullException("input");
192 }
193
194 input = input.TrimEnd('='); //remove padding characters
195 int byteCount = input.Length * 5 / 8; //this must be TRUNCATED
196 byte[] returnArray = new byte[byteCount];
197
198 byte curByte = 0, bitsRemaining = 8;
199 int mask = 0, arrayIndex = 0;
200
201 foreach (char c in input)
202 {
203 int cValue = CharToValue(c);
204
205 if (bitsRemaining > 5)
206 {
207 mask = cValue << (bitsRemaining - 5);
208 curByte = (byte)(curByte | mask);
209 bitsRemaining -= 5;
210 }
211 else
212 {
213 mask = cValue >> (5 - bitsRemaining);
214 curByte = (byte)(curByte | mask);
215 returnArray[arrayIndex++] = curByte;
216 curByte = (byte)(cValue << (3 + bitsRemaining));
217 bitsRemaining += 3;
218 }
219 }
220
221 //if we didn't end with a full byte
222 if (arrayIndex != byteCount)
223 {
224 returnArray[arrayIndex] = curByte;
225 }
226
227 return returnArray;
228 }
229
230 /// <summary>
231 /// byte[] to Base32 string, if starting from an ordinary string use Encoding.UTF8.GetBytes() to convert it to a byte[]
232 /// </summary>
233 /// <param name="input">byte[] of data to be Base32 encoded</param>
234 /// <returns>Base32 String</returns>
235 public static string ToString(byte[] input)
236 {
237 if (input == null || input.Length == 0)
238 {
239 throw new ArgumentNullException("input");
240 }
241
242 int charCount = (int)Math.Ceiling(input.Length / 5d) * 8;
243 char[] returnArray = new char[charCount];
244
245 byte nextChar = 0, bitsRemaining = 5;
246 int arrayIndex = 0;
247
248 foreach (byte b in input)
249 {
250 nextChar = (byte)(nextChar | (b >> (8 - bitsRemaining)));
251 returnArray[arrayIndex++] = ValueToChar(nextChar);
252
253 if (bitsRemaining < 4)
254 {
255 nextChar = (byte)((b >> (3 - bitsRemaining)) & 31);
256 returnArray[arrayIndex++] = ValueToChar(nextChar);
257 bitsRemaining += 5;
258 }
259
260 bitsRemaining -= 3;
261 nextChar = (byte)((b << bitsRemaining) & 31);
262 }
263
264 //if we didn't end with a full char
265 if (arrayIndex != charCount)
266 {
267 returnArray[arrayIndex++] = ValueToChar(nextChar);
268 while (arrayIndex != charCount) returnArray[arrayIndex++] = '='; //padding
269 }
270
271 return new string(returnArray);
272 }
273
274 private static int CharToValue(char c)
275 {
276 int value = (int)c;
277
278 //65-90 == uppercase letters
279 if (value < 91 && value > 64)
280 {
281 return value - 65;
282 }
283 //50-55 == numbers 2-7
284 if (value < 56 && value > 49)
285 {
286 return value - 24;
287 }
288 //97-122 == lowercase letters
289 if (value < 123 && value > 96)
290 {
291 return value - 97;
292 }
293
294 throw new ArgumentException("Character is not a Base32 character.", "c");
295 }
296
297 private static char ValueToChar(byte b)
298 {
299 if (b < 26)
300 {
301 return (char)(b + 65);
302 }
303
304 if (b < 32)
305 {
306 return (char)(b + 24);
307 }
308
309 throw new ArgumentException("Byte is not a value Base32 value.", "b");
310 }
311 }
测试代码如下：
1 // 密钥
2 private string key = "123456";
3
4 // 生成新的二维码
5 private void ButtonBase_OnClick1(object sender, RoutedEventArgs e)
6 {
7 // 发行人
8 string issuer = TextBoxIssuer.Text;
9
10 //登陆账号名称
11 string user = TextBoxUser.Text;
12
13 // 生成 SetupCode
14 var code = new GoogleAuthenticator().GenerateSetupCode(issuer, user, key, 5);
15
16 // 转换成位图
17 var img = GoogleAuthenticator.GetQRCodeImage(code.QrCodeSetupImageUrl);
18
19 // 展示位图
20 {
21 Bitmap bitmap = img as Bitmap;
22 IntPtr myImagePtr = bitmap.GetHbitmap();
23 ImageSource imgsource = System.Windows.Interop.Imaging.CreateBitmapSourceFromHBitmap(myImagePtr, IntPtr.Zero, Int32Rect.Empty, BitmapSizeOptions.FromEmptyOptions()); //创建imgSource
24 ImageQRCode.Source = imgsource;
25 }
26 }
27
28 // 验证校验
29 private void ButtonBase_OnClick(object sender, RoutedEventArgs e)
30 {
31 string token = TextBoxToken.Text;
32 if (string.IsNullOrEmpty(token) == false)
33 {
34 GoogleAuthenticator gat = new GoogleAuthenticator();
35 var result = gat.ValidateTwoFactorPIN(key, token.ToString());
36 if (result)
37 {
38 MessageBox.Show("动态码校验通过！", "提示信息", MessageBoxButton.OK, MessageBoxImage.Question);
39 }
40 else
41 {
42 MessageBox.Show("动态码校验未通过！", "提示信息", MessageBoxButton.OK, MessageBoxImage.Warning);
43 }
44 }
45 }