Keychain的使用

之前做项目，用户保存账号密码都会保存到NSUserdefault中，每次卸载了app后，数据都会随之清除，而且不安全。后来系统就提供了keychain作为存储账号，密码，网络密码，认证令牌的工具，然后项目中就开始使用keychain来存储敏感信息，这些数据存储之后即使卸载了app也不会被清除。
下面就先来说说keychain的用法。
引入头文件#import <Security/Security.h>

NSString * const KEY_USERNAME_PASSWORD = @"com.company.app.usernamepassword";

+ (void)keyChainSave:(NSString *)string {
  NSMutableDictionary *tempDic = [NSMutableDictionary dictionary];
  [tempDic setObject:string forKey:kSYDictionaryKey];
//    [self save:kSYKeyChainKey data:tempDic];
  [self setSaveObject:tempDic forKey:kSYKeyChainKey];
}

+ (NSString *)keyChainLoad{
  NSMutableDictionary *tempDic = (NSMutableDictionary *)[self objectForKey:kSYKeyChainKey];
//    [self load:kSYKeyChainKey];
  return [tempDic objectForKey:kSYDictionaryKey];
}

+ (void)keyChainDelete{
  [self removeObjectForKey:kSYKeyChainKey];
}

+ (NSMutableDictionary *)getKeychainQuery:(NSString *)service {
  return [NSMutableDictionary dictionaryWithObjectsAndKeys:
          (id)kSecClassGenericPassword,(id)kSecClass,
          service, (id)kSecAttrService,
          service, (id)kSecAttrAccount,
          (id)kSecAttrAccessibleAfterFirstUnlock,(id)kSecAttrAccessible,
          nil];
}

+ (void)setSaveObject:(id )value forKey:(NSString *)forKey{
  
  //Get search dictionary
  NSMutableDictionary *keychainQuery = [self getKeychainQuery:forKey];
  //Delete old item before add new item
  SecItemDelete((CFDictionaryRef)keychainQuery);
  //Add new object to search dictionary(Attention:the data format)
  [keychainQuery setObject:[NSKeyedArchiver archivedDataWithRootObject:value] forKey:(id)kSecValueData];
  //Add item to keychain with the search dictionary
  SecItemAdd((CFDictionaryRef)keychainQuery, NULL);
}

+ (id)objectForKey:(NSString *)service {
  id ret = nil;
  NSMutableDictionary *keychainQuery = [self getKeychainQuery:service];
  //Configure the search setting
  //Since in our simple case we are expecting only a single attribute to be returned (the password) we can set the attribute kSecReturnData to kCFBooleanTrue
  [keychainQuery setObject:(id)kCFBooleanTrue forKey:(id)kSecReturnData];
  [keychainQuery setObject:(id)kSecMatchLimitOne forKey:(id)kSecMatchLimit];
  CFDataRef keyData = NULL;
  if (SecItemCopyMatching((CFDictionaryRef)keychainQuery, (CFTypeRef *)&keyData) == noErr) {
      @try {
          ret = [NSKeyedUnarchiver unarchiveObjectWithData:(__bridge NSData *)keyData];
      } @catch (NSException *e) {
          NSLog(@"Unarchive of %@ failed: %@", service, e);
      } @finally {
      }
  }
  if (keyData)
      CFRelease(keyData);
  return ret;
}

+ (void)removeObjectForKey:(NSString *)service {
  NSMutableDictionary *keychainQuery = [self getKeychainQuery:service];
  SecItemDelete((CFDictionaryRef)keychainQuery);
  
  
}

  看完这些代码，可以发现keychain类似于数据库，有增删改查功能。

就这样，利用keychain很方便的保存了用户的登录信息，但是我们的项目又要求当用户卸载app重新安装后，不能保留用户信息。所以对于keychain，我百度搜了很多，但是都是不能清除。
最后想到一种办法，就是利用NSUserDefault看是否首次安装或重新安装，移除用户名，用户密码。

if (![[NSUserDefaults standardUserDefaults] objectForKey:@"FirstInstall"]) {
      [[NSUserDefaults standardUserDefaults] setValue:@"isFirst" forKey:@"FirstInstall"];
      [[NSUserDefaults standardUserDefaults] synchronize];
//首次安装，移除用户名，用户密码
      [SYKeyChain removeObjectForKey:SYSaveAuthTokenKey_account];
      [SYKeyChain removeObjectForKey:SYSaveAuthTokenKey_passwordTF];
      

  }

注意，在.m中定义KEY_USERNAME_PASSWORD以上数据，如果要在其他页面用，要在.h中
UIKIT_EXTERN NSString *const KEY_USERNAME_PASSWORD;这样定义，然后在其他页面导入此控制器才行。