一、Google Authenticator 基本概念
Google Authenticator是谷歌推出的一款動態口令工具，旨在解決大家Google賬戶遭到惡意攻擊的問題，在手機端生成動態口令后，在Google相關的服務登陸中除了用正常用戶名和密碼外，需要輸入一次動態口令才能驗證成功，此舉是為了保護用戶的信息安全。
谷歌驗證（Google Authenticator）通過兩個驗證步驟，在登錄時為用戶的谷歌帳號提供一層額外的安全保護。使用谷歌驗證可以直接在用戶的設備上生成動態密碼，無需網絡連接。其基本步驟如下：
- 使用google authenticator PAM插件為登錄賬號生成動態驗證碼。
- 手機安裝Google身份驗證器，通過此工具掃描上一步生成的二維碼圖形，獲取動態驗證碼。
當用戶在Google帳號中啟用“兩步驗證”功能后，就可以使用Google Authenticator來防止陌生人通過盜取的密碼訪問用戶的帳戶。通過兩步驗證流程登錄時，用戶需要同時使用密碼和通過手機產生的動態密碼來驗證用戶的身份。也就是說，即使可能的入侵者竊取或猜出了用戶的密碼，也會因不能使用用戶的手機而無法登錄帳戶。
更多原理可以查看閱讀“詳解Google Authenticator工作原理”。
二、.NET 使用 Google Authenticator
第一步，通過 Nuget 下載 Google Authenticator 安裝包
第二步，例如我們要實現這樣的功能：手機掃描 PC 生成的二維碼，綁定用戶信息后，后續使用手機生成的驗證碼輸入到 PC 端進行校驗。我們通過編程生成一個二維碼如下圖所示：
第三步：安裝 Google Authenticator APP，安卓版下載、IOS下載（注意：安卓版本下載需FQ）。安裝成功后，掃描上圖的二維碼添加如下：
第四步：輸入生成的驗證碼，在 PC 端輸入口令后，展示校驗通過（注意：口令有效時間為30秒）。
Google Authenticator 在 PC 端生成二維碼、手機上生成驗證碼、 PC 端校驗驗證碼，這些過程無需網絡，只需要保證 PC 時間和手機時間正確一致即可。
Google Authenticator 工具類代碼如下（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 }
測試代碼如下：
1 // 密鑰
2 private string key = "123456";
3
4 // 生成新的二維碼
5 private void ButtonBase_OnClick1(object sender, RoutedEventArgs e)
6 {
7 // 發行人
8 string issuer = TextBoxIssuer.Text;
9
10 //登陸賬號名稱
11 string user = TextBoxUser.Text;
12
13 // 生成 SetupCode
14 var code = new GoogleAuthenticator().GenerateSetupCode(issuer, user, key, 5);
15
16 // 轉換成位圖
17 var img = GoogleAuthenticator.GetQRCodeImage(code.QrCodeSetupImageUrl);
18
19 // 展示位圖
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()); //創建imgSource
24 ImageQRCode.Source = imgsource;
25 }
26 }
27
28 // 驗證校驗
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("動態碼校驗通過！", "提示信息", MessageBoxButton.OK, MessageBoxImage.Question);
39 }
40 else
41 {
42 MessageBox.Show("動態碼校驗未通過！", "提示信息", MessageBoxButton.OK, MessageBoxImage.Warning);
43 }
44 }
45 }