KeyChain是蘋果提供的一種安全的保存用戶名、密碼、證書的方式，將敏感信息保存在keychain中後，這些信息不會隨著app的卸載而丟失，除非開發人員在app中手動刪除敏感信息，否則，這些信息將會一直保存在keychain中。

在使用keychain時，我們首先要將security.framework引入到工程中。由於使用時不支持arc，所以我們在arc環境中需要針對相關文件啟用mrc模式。

首先，我們構造一個工具類，通過這個類來操作keychain。

 

#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

在實現文件中，我們這樣寫：

 

 

#import "KeyChain.h"

@implementation KeyChain

        /**
         *該類需要工作在mrc模式下，acr的項目按照如下步驟操作
         *選中工程->TARGETS->相應的target然後選中右側的“Build Phases”，向下就找到“Compile Sources”了。然後在相應的文件後面添加:-fno-objc-arc參數
         *
        **/



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


@end

修改工程的相關放在在代碼注釋中已經寫清楚了。

 

下邊是使用這個類

首先，我們定義幾個字符串類型的標識符

 

    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";

之後，我們創建一個字典，並將用戶名和密碼放入字典中

 

 

    NSMutableDictionary *userNamePasswordKVPairs = [NSMutableDictionary dictionary];
    [userNamePasswordKVPairs setObject:@"userName" forKey:KEY_USERNAME];
    [userNamePasswordKVPairs setObject:@"password" forKey:KEY_PASSWORD];

下邊引用工具類的各個方法，分別進行用戶名和密碼的添加、讀取、刪除操作

 

 

 // A、將用戶名和密碼寫入keychain
    [KeyChain save:KEY_USERNAME_PASSWORD data:userNamePasswordKVPairs];
    
    // B、從keychain中讀取用戶名和密碼
    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、將用戶名和密碼從keychain中刪除
    [KeyChain delete:KEY_USERNAME_PASSWORD];

keychain的用法還有很多，我們在這裡只是簡單的將用戶名和密碼保存在keychain，而不是數據庫或nsuserdefaults中，以增加安全性。