iOS8指紋識別TouchID

      蘋果在2014年6月3日的WWDC2014開幕式上推出了新版iOS8系統，界面上iOS8與iOS7相比變化不大，只是在功能方面進行了無缺。iOS8通知中心更增強大，支持消息直接回復操做，並支持QuickType和第三方輸入法。短信功能改進明顯，支持羣聊。發送語音、視頻，分享地理位置等。從終端用戶的角度看。iOS8的不少新功能早已出現在其它平臺中。iOS8會向第三方軟件開放TouchID訪問，這意味着可以使用該感應器登錄銀行應用等。

      第三方應用可以使用TouchID接口，意味着將來的很是多應用都可以用指紋識別功能了。你可以選擇Touch ID登錄第三方應用程序，不需要輸入password，你的指紋數據是被保護的，在沒有被贊成的狀況下別的程序是訪問不到它的。

                                

      依據蘋果的解釋，一個單一的註冊指紋與別人指紋出現隨機匹配的機率爲五萬分之中的一個。

      蘋果聲稱「Secure Enclave」模塊系統能夠安全地管理並識別用戶的指紋，並將用戶的指紋信息獨立地保存在別的系統中。同一時候經過加密內存和一個硬件隨機數字password發生器進行管理。

      每個「Secure Enclave」是單獨設置的。不能訪問系統其它部分的，擁有本身的獨立的UID（惟一的ID），連蘋果也不知道這些UID。當設備啓動時，Touch ID會暫時建立一個祕鑰，與「Secure Enclave」的UID配合，對設備的內存空間進行加密。

      而在蘋果公佈的文件裏。蘋果對A7處理器進行指紋識別受權的描寫敘述是：A7和Touch ID之間經過一個串行外設接口總線進行通訊。A7處理器將數據發到「Secure Enclave」。但並不正確數據內容進行讀取。加密和身份驗證都是使用Touch ID和「Secure Enclave」之間的共享密鑰。

通訊密鑰交換使用兩方提供的一個隨機AES密鑰，並隨機創建會話密鑰和使用AES-CCM傳輸加密。

      據瞭解：iPhone 5s中的指紋傳感器檢測到的表皮上突起的紋線。

它檢測到的不是用戶手指外部的死皮指紋，這樣的指紋很是easy被複制。iPhone 5s的指紋傳感器利用射頻信號。檢測用戶手指表面下方那一層皮膚的「活」指紋。假設手指與人的身體分離，那麼傳感器是沒法檢測到這樣的指紋的。因此用戶不用操心本身的指紋被複制或盜竊以後，被用於解鎖設備，因爲傳感器是沒法識別這樣的「死」指紋的。

      近期研究了下iOS8的文檔，對指紋識別瞭解了下，並下載了一個官方提供的Demo。但是

      NS_CLASS_AVAILABLE(10_10, 8_0)

      從這句中可以看出，要想使用TouchID的接口，電腦的mac系統必須是10.10的，手機iOS系統必須是8.0，因此爲了這個Demo我也沒有升級電腦系統(畢竟還不穩定)。

但依據Demo中的代碼和文檔可以看出，TouchID的基本使用方法。

1.首先要使用TouchID。要先導入依賴包：LocalAuthentication.framework。

2.檢查設備可否用TouchID，返回檢查結果BOOL類型success：

LAContext *context = [[LAContext alloc] init];
    __block  NSString *msg;
    NSError *error;
    BOOL success;
    
    // test if we can evaluate the policy, this test will tell us if Touch ID is available and enrolled
    success = [context canEvaluatePolicy: LAPolicyDeviceOwnerAuthenticationWithBiometrics error:&error];
    if (success) {
        msg =[NSString stringWithFormat:NSLocalizedString(@"TOUCH_ID_IS_AVAILABLE", nil)];
    } else {
        msg =[NSString stringWithFormat:NSLocalizedString(@"TOUCH_ID_IS_NOT_AVAILABLE", nil)];
    }

3.假設設備能使用TouchID。代碼塊中返回識別結果BOOL類型的success：

LAContext *context = [[LAContext alloc] init];
    __block  NSString *msg;
    
    // show the authentication UI with our reason string
    [context evaluatePolicy:LAPolicyDeviceOwnerAuthenticationWithBiometrics localizedReason:NSLocalizedString(@"UNLOCK_ACCESS_TO_LOCKED_FATURE", nil) reply:
     ^(BOOL success, NSError *authenticationError) {
         if (success) {
             msg =[NSString stringWithFormat:NSLocalizedString(@"EVALUATE_POLICY_SUCCESS", nil)];
         } else {
             msg = [NSString stringWithFormat:NSLocalizedString(@"EVALUATE_POLICY_WITH_ERROR", nil), authenticationError.localizedDescription];
         }
     }];

4.對於檢查和識別的兩個方法在 LocalAuthentication.framework/Headers/LAContext.h 中定義的：

/// Determines if a particular policy can be evaluated.
///
/// @discussion Policies can have certain requirements which, when not satisfied, would always cause
///             the policy evaluation to fail. Examples can be a passcode set or a fingerprint
///             enrolled with Touch ID. This method allows easy checking for such conditions.
///
///             Applications should consume the returned value immediately and avoid relying on it
///             for an extensive period of time. At least, it is guaranteed to stay valid until the
///             application enters background.
///
/// @warning    Do not call this method in the reply block of evaluatePolicy:reply: because it could
///             lead to a deadlock.
///
/// @param policy Policy for which the preflight check should be run.
///
/// @param error Optional output parameter which is set to nil if the policy can be evaluated, or it
///              contains error information if policy evaluation is not possible.
///
/// @return YES if the policy can be evaluated, NO otherwise.
- (BOOL)canEvaluatePolicy:(LAPolicy)policy error:(NSError * __autoreleasing *)error;

/// Evaluates the specified policy.
///
/// @discussion Policy evaluation may involve prompting user for various kinds of interaction
///             or authentication. Actual behavior is dependent on evaluated policy, device type,
///             and can be affected by installed configuration profiles.
///
///             Be sure to keep a strong reference to the context while the evaluation is in progress.
///             Otherwise, an evaluation would be canceled when the context is being deallocated.
///
///             The method does not block. Instead, the caller must provide a reply block to be
///             called asynchronously when evaluation finishes. The block is executed on a private
///             queue internal to the framework in an unspecified threading context. Other than that,
///             no guarantee is made about which queue, thread, or run-loop the block is executed on.
///
///             Implications of successful policy evaluation are policy specific. In general, this
///             operation is not idempotent. Policy evaluation may fail for various reasons, including
///             user cancel, system cancel and others, see LAError codes.
///
/// @param policy Policy to be evaluated.
///
/// @param reply Reply block that is executed when policy evaluation finishes.
///
/// @param localizedReason Application reason for authentication. This string must be provided in correct
///                        localization and should be short and clear. It will be eventually displayed in
///                        the authentication dialog subtitle. A name of the calling application will be
///                        already displayed in title, so it should not be duplicated here.
///
/// @param success Reply parameter that is YES if the policy has been evaluated successfully or NO if
///                the evaluation failed.
///
/// @param error Reply parameter that is nil if the policy has been evaluated successfully, or it contains
///              error information about the evaluation failure.
///
/// @warning localizedReason parameter is mandatory and the call will throw NSInvalidArgumentException if
///          nil or empty string is specified.
///
/// @see LAError
///
/// Typical error codes returned by this call are:
/// @li          LAErrorUserFallback if user tapped the fallback button
/// @li          LAErrorUserCancel if user has tapped the Cancel button
/// @li          LAErrorSystemCancel if some system event interrupted the evaluation (e.g. Home button pressed).
- (void)evaluatePolicy:(LAPolicy)policy localizedReason:(NSString *)localizedReason reply:(void(^)(BOOL success, NSError *error))reply;

歡迎小夥伴們對測試結果檢驗一下啊！

（轉載請註明出處，謝謝！

http://blog.csdn.net/yujianxiang666/article/details/35280025）