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Keychain介绍与使用

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介绍

引言：

Mac OS可以利用KeyChain保存各应用中用户的账号密码，让用户不用重复输入。其实在iOS中也有KeyChain，也可以用KeyChain在应用间共享数据，只是有一些限制，无法像Mac OS一样开放，也无法让用户手动控制。那么KeyChain到底如何使用呢？

我们可以把KeyChain理解为一个Dictionary，所有数据都以key-value的形式存储，可以对这个Dictionary进行add、update、get、delete这四个操作。对于每一个应用来说，KeyChain都有两个访问区，私有区和公共区。私有区是一个sandbox，本程序存储的任何数据都对其他程序不可见。而要想在将存储的内容放在公共区，需要先声明公共区的名称，官方文档管这个名称叫“keychain access group”

使用

通常情况下，我们用NSUserDefaults存储数据信息，但是对于一些私密信息，比如密码、证书等等，就需要使用更为安全的keychain了。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。

使用苹果官方发布的KeychainItemWrapper或者SFHFKeychainUtils很方便，后来看到 iphone使用keychain来存取用户名和密码 一文，觉得对了解keychain有很大的帮助，于是ARC控也尝试了一把。

需要导入Security.framework

@implementation WQKeyChain
+ (NSMutableDictionary *)getKeychainQuery:(NSString *)service {
return [NSMutableDictionary dictionaryWithObjectsAndKeys:
        (__bridge_transfer id)kSecClassGenericPassword,(__bridge_transfer id)kSecClass,
        service, (__bridge_transfer id)kSecAttrService,
        service, (__bridge_transfer id)kSecAttrAccount,
        (__bridge_transfer id)kSecAttrAccessibleAfterFirstUnlock,(__bridge_transfer 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((__bridge_retained CFDictionaryRef)keychainQuery);
    //Add new object to search dictionary(Attention:the data format)
    [keychainQuery setObject:[NSKeyedArchiver archivedDataWithRootObject:data] forKey:(__bridge_transfer id)kSecValueData];
    //Add item to keychain with the search dictionary
    SecItemAdd((__bridge_retained CFDictionaryRef)keychainQuery, NULL);
}

+ (id)load:(NSString *)service {
    id ret = nil;
    NSMutableDictionary *keychainQuery = [self getKeychainQuery:service];
    //Configure the search setting
    [keychainQuery setObject:(id)kCFBooleanTrue forKey:(__bridge_transfer id)kSecReturnData];
    [keychainQuery setObject:(__bridge_transfer id)kSecMatchLimitOne forKey:(__bridge_transfer id)kSecMatchLimit];
    CFDataRef keyData = NULL;
    if (SecItemCopyMatching((__bridge_retained CFDictionaryRef)keychainQuery, (CFTypeRef *)&keyData) == noErr) {
        @try {
            ret = [NSKeyedUnarchiver unarchiveObjectWithData:(__bridge_transfer NSData *)keyData];
        } @catch (NSException *e) {
            NSLog(@"Unarchive of %@ failed: %@", service, e);
        } @finally {
        }
    }
    return ret;
}

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

比如，保存密码

@interface WQUserDataManager : NSObject


+(void)savePassWord:(NSString *)password;


+(id)readPassWord;


+(void)deletePassWord;

@end

#import "WQUserDataManager.h"

@implementation WQUserDataManager

static NSString * const KEY_IN_KEYCHAIN = @"com.wuqian.app.allinfo";
static NSString * const KEY_PASSWORD = @"com.wuqian.app.password";

+(void)savePassWord:(NSString *)password
{
    NSMutableDictionary *usernamepasswordKVPairs = [NSMutableDictionary dictionary];
    [usernamepasswordKVPairs setObject:password forKey:KEY_PASSWORD];
    [WQKeyChain save:KEY_IN_KEYCHAIN data:usernamepasswordKVPairs];
}

+(id)readPassWord
{
    NSMutableDictionary *usernamepasswordKVPair = (NSMutableDictionary *)[WQKeyChain load:KEY_IN_KEYCHAIN];
    return [usernamepasswordKVPair objectForKey:KEY_PASSWORD];
}

+(void)deletePassWord
{
    [WQKeyChain delete:KEY_IN_KEYCHAIN];
}
@end

实现一个简单的界面，把设定的密码存起来，然后立即读取显示出来看看效果

-(IBAction)btnAciton:(id)sender
{
    [WQUserDataManager savePassWord:self.textfield.text];
    self.label.text = [WQUserDataManager readPassWord];
}
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