使用Keychain存储用户敏感信息

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。keyChain是苹果提供的一种安全的保存用户名、密码、证书的方式，将敏感信息保存在keychain中后，这些信息不会随着app的卸载而丢失，除非开发人员在app中手动删除敏感信息，否则，这些信息将会一直保存在keychain中。

** 在使用keychain时，我们首先要将security.framework引入到工程中**

自定义一个类，取名KeyChain，头文件.h如下：

#import 
#import 
@interface KeyChain : NSObject

// save username and password to keychain
+ (void)save:(NSString *)service data:(id)data;

// take out username and passwore from keychain
+ (id)load:(NSString *)service;

// delete username and password from keychain
+ (void)delete:(NSString *)service;

@end

在实现文件中.m中，我们这样写：

#import "KeyChain.h"

@implementation KeyChain


+ (NSMutableDictionary *)getKeychainQuery:(NSString *)service {
    return [NSMutableDictionary dictionaryWithObjectsAndKeys:
            (id)kSecClassGenericPassword,(id)kSecClass,
            service, (id)kSecAttrService,
            service, (id)kSecAttrAccount,
            (id)kSecAttrAccessibleAfterFirstUnlock,(id)kSecAttrAccessible,
            nil];
}
#pragma mark 写入
+ (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);
}
#pragma mark 读取
+ (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:(__bridge NSData *)keyData];
        } @catch (NSException *e) {
            NSLog(@"Unarchive of %@ failed: %@", service, e);
        } @finally {
        }
    }
    if (keyData)
        CFRelease(keyData);
    return ret;
}
#pragma mark 删除
+ (void)delete:(NSString *)service {
    NSMutableDictionary *keychainQuery = [self getKeychainQuery:service];
    SecItemDelete((CFDictionaryRef)keychainQuery);
}
@end

下边是使用这个类,在viewController中，我们定义几个字符串类型的标识符

#import "ViewController.h"
#import "KeyChain.h"
@interface ViewController ()

@end
NSString * const KEY_USERNAME_PASSWORD = @"com.company.app.usernamepassword";
NSString * const KEY_USERNAME = @"com.company.app.username";
NSString * const KEY_PASSWORD = @"com.company.app.password";
@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    NSMutableDictionary *userNamePasswordKVPairs = [NSMutableDictionary dictionary];
    [userNamePasswordKVPairs setObject:@"userName" forKey:KEY_USERNAME];
    [userNamePasswordKVPairs setObject:@"password" forKey:KEY_PASSWORD];
    // Do any additional setup after loading the view, typically from a nib.
    
    
    // A、将用户名和密码写入keychain
    [KeyChain save:KEY_USERNAME_PASSWORD data:userNamePasswordKVPairs];
    
    // B、从keychain中读取用户名和密码
    NSMutableDictionary *readUsernamePassword = (NSMutableDictionary *)[KeyChain load:KEY_USERNAME_PASSWORD];
    NSString *userName = [readUsernamePassword objectForKey:KEY_USERNAME];
    NSString *password = [readUsernamePassword objectForKey:KEY_PASSWORD];
    NSLog(@"username = %@", userName);
    NSLog(@"password = %@", password);
    
    // C、将用户名和密码从keychain中删除
    [KeyChain delete:KEY_USERNAME_PASSWORD];

}

运行结果如下：

2016-08-15 16:36:08.588 KeyChain[8563:1595142] username = userName
2016-08-15 16:36:08.589 KeyChain[8563:1595142] password = password