keychain的功能简介

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keychain（钥匙串）提供了一种安全的保存私密信息（密码，序列号，证书等）的方式。即使重新安装程序保存过的密码也不会丢失。

keychain可以安全的记录用户的密码，其中keychain保存的密码文件都是经过加密的，通常情况下即使直接打开这个加密文件也获取不到keychain中的密码。

Apple提供了使用keychain的API，详细可见：Keychain Services Reference

IOS中keychain与NSUserdefaults相比

NSUserdefaults适用于保存轻量级的数据，加载NSUserdefaults中的数据相对要快一些，数据以明文的形式保存在plist文件，所以不适合用来保存密码。文件的位置是Library/Application Support/iPhone Simulator/模拟器版本/Applications/应用对应的数字/Library/Preference/.plist文件

keychain采用的是将数据加密之后再保存到本地的，这样对数据而言有更高的安全性，适合保存密码之类的数据。数据保存的目录是Library/Application Support/iPhone Simulator/模拟器版本/Library/Keychains/

使用方法：

在工程中导入Security.framework

代码：

CHKeychain.h

   1:  #import <Foundation/Foundation.h>

   2:  #import <Security/Security.h>

3:

4:

   5:  @interface CHKeychain : NSObject

6:

   7:  + (void)save:(NSString *)service data:(id)data;

   8:  + (id)load:(NSString *)service;

   9:  + (void)delete:(NSString *)service;

10:

11:

  12:  @end

CHKeychain.m

   1:  #import "CHKeychain.h"

2:

   3:  @implementation CHKeychain

   4:  + (NSMutableDictionary *)getKeychainQuery:(NSString *)service {

   5:      return [NSMutableDictionary dictionaryWithObjectsAndKeys:

   6:              (id)kSecClassGenericPassword,(id)kSecClass,

   7:              service, (id)kSecAttrService,

   8:              service, (id)kSecAttrAccount,

   9:              (id)kSecAttrAccessibleAfterFirstUnlock,(id)kSecAttrAccessible,

  10:              nil];

  11:  }

12:

  13:  + (void)save:(NSString *)service data:(id)data {

  14:      //Get search dictionary

  15:      NSMutableDictionary *keychainQuery = [self getKeychainQuery:service];

  16:      //Delete old item before add new item

  17:      SecItemDelete((CFDictionaryRef)keychainQuery);

  18:      //Add new object to search dictionary(Attention:the data format)

  19:      [keychainQuery setObject:[NSKeyedArchiver archivedDataWithRootObject:data] forKey:(id)kSecValueData];

  20:      //Add item to keychain with the search dictionary

  21:      SecItemAdd((CFDictionaryRef)keychainQuery, NULL);

  22:  }

23:

  24:  + (id)load:(NSString *)service {

  25:      id ret = nil;

  26:      NSMutableDictionary *keychainQuery = [self getKeychainQuery:service];

  27:      //Configure the search setting

  28:      //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

  29:      [keychainQuery setObject:(id)kCFBooleanTrue forKey:(id)kSecReturnData];

  30:      [keychainQuery setObject:(id)kSecMatchLimitOne forKey:(id)kSecMatchLimit];

  31:      CFDataRef keyData = NULL;

  32:      if (SecItemCopyMatching((CFDictionaryRef)keychainQuery, (CFTypeRef *)&keyData) == noErr) {

  33:          @try {

  34:              ret = [NSKeyedUnarchiver unarchiveObjectWithData:(NSData *)keyData];

  35:          } @catch (NSException *e) {

  36:              NSLog(@"Unarchive of %@ failed: %@", service, e);

  37:          } @finally {

  38:  }

  39:      }

  40:      if (keyData)

  41:      CFRelease(keyData);

  42:      return ret;

  43:  }

44:

  45:  + (void)delete:(NSString *)service {

  46:      NSMutableDictionary *keychainQuery = [self getKeychainQuery:service];

  47:      SecItemDelete((CFDictionaryRef)keychainQuery);

  48:  }

49:

50:

  51:  @end

１．定义几个字符串用来做key：

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

   2:  NSString * const KEY_USERNAME = @"com.company.app.username";

   3:  NSString * const KEY_PASSWORD = @"com.company.app.password";

2. 把用户名和密码存入keychain：

   1:  NSMutableDictionary *usernamepasswordKVPairs = [NSMutableDictionary dictionary];

   2:  [usernamepasswordKVPairs setObject:txtfldUsername.text forKey:KEY_USERNAME];

   3:  [usernamepasswordKVPairs setObject:txtfldPassword.text forKey:KEY_PASSWORD];

   4:  [CHKeychain save:KEY_USERNAME_PASSWORD data:usernamepasswordKVPairs];

3. 从keychain中取出用户名和密码：

   1:  NSMutableDictionary *usernamepasswordKVPairs = (NSMutableDictionary *)[CHKeychain load:KEY_USERNAME_PASSWORD];

   2:  txtfldUsername.text = [usernamepasswordKVPairs objectForKey:KEY_USERNAME];

   3:  txtfldPassword.text = [usernamepasswordKVPairs objectForKey:KEY_PASSWORD];

4. 删除一个keychain item:

   1:  [CHKeychain delete:KEY_USERNAME_PASSWORD];