Tips:在实习过程中，有个需求是实现App的七天免登陆。当时的想法是用NSUserDefaults存储，用NSDate判断时间，取七天的间隔判断登陆状态。现在想想用NSUserDefaults直接存储用户信息是非常不安全的。通常情况下，可以用NSUserDefaults存储数据信息，但是对于一些私密信息，比如账号、密码等等，就需要使用更为安全的KeyChain了。而KeyChain的信息是存在于每个应用（app）的沙盒之外的，所以KeyChain里保存的信息不会因App被删除而丢失，在用户重新安装App后依然有效，数据还在。

2016.12.22最新更新
最近一直有朋友说不知道怎么用，特来更新了 PDKeyChain，添加了注释，有问题可以提 issue 欢迎讨论。

2016.8.23最新更新
最近一直有朋友问源码，整理了一下发在这里。

2016.3.23最新更新
近期项目中又用到keychain，于是回头翻了翻以前写的代码，感觉写的/(ㄒoㄒ)/~~
设计不科学，命名不规范，怎么看怎么别扭，那就重写吧~

KeyChain

话不多说，咱们直接来看怎么快速集成KeyChain。

  1. 自定义一个类，取名XXXKeyChain，如下：
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#import <Foundation/Foundation.h>
#import <Security/Security.h>
#define KEY_PASSWORD  @"com.rry.app.password"
#define KEY_USERNAME_PASSWORD  @"com.rry.app.usernamepassword"
@interface RRYKeyChain : NSObject
+ (void)save:(NSString *)service data:(id)data;
+ (id)load:(NSString *)service;
+ (void)delete:(NSString *)service;
@end

以上代码自定义了三个方法，存、取、删。并且定义了几个字符串用来做key。当然，想使用keychain请不要忘记引入Security包，引入文件 #import<Security/Security.h>。

  1. 再来看.m文件的具体实现
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#import "RRYKeyChain.h"

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

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

+ (id)load:(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:(NSData *)keyData];
        } @catch (NSException *e) {
            NSLog(@"Unarchive of %@ failed: %@", service, e);
        } @finally {
        }
    }
    if (keyData)
        CFRelease(keyData);
    return ret;
}

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

然后就是存，其中password是要存的密码字符串。

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NSMutableDictionary *usernamepasswordKVPairs = [NSMutableDictionary dictionary];
[usernamepasswordKVPairs setObject:password forKey:KEY_PASSWORD];
[RRYKeyChain save:KEY_USERNAME_PASSWORD data:usernamepasswordKVPairs];

取

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

NSLog(@"%@",[usernamepasswordKVPairs objectForKey:KEY_PASSWORD]);

删

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[RRYKeyChain delete:KEY_USERNAME_PASSWORD];

搞定收工，使用KeyChain快速存储密码。

2016.3.23最新更新

话不多说，直接上代码，首先是.h

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#import <Foundation/Foundation.h>
#import <Security/Security.h>

@interface RHKeyChain : NSObject

+ (void)rhKeyChainSave:(NSString *)service;

+ (NSString *)rhKeyChainLoad;

+ (void)rhKeyChainDelete:(NSString *)service;

@end

只对外提供三个方法，存、取、删，实现放在内部，再是.m

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static NSString * const kRHDictionaryKey = @"com.xxxx.dictionaryKey";
static NSString * const kRHKeyChainKey = @"com.xxxx.keychainKey";

+ (void)rhKeyChainSave:(NSString *)service {
    NSMutableDictionary *tempDic = [NSMutableDictionary dictionary];
    [tempDic setObject:service forKey:kRHDictionaryKey];
    [self save:kRHKeyChainKey data:tempDic];
}

+ (NSString *)rhKeyChainLoad{
    NSMutableDictionary *tempDic = (NSMutableDictionary *)[self load:kRHKeyChainKey];
    return [tempDic objectForKey:kRHDictionaryKey];
}

+ (void)rhKeyChainDelete{
    [self delete:kRHKeyChainKey];
}

三个方法的实现。