// 查询
OSStatus SecItemCopyMatching(CFDictionaryRef query, CFTypeRef *result);

// 添加
OSStatus SecItemAdd(CFDictionaryRef attributes, CFTypeRef *result);

// 更新KeyChain中的Item
OSStatus SecItemUpdate(CFDictionaryRef query, CFDictionaryRef attributesToUpdate);

// 删除KeyChain中的Item
OSStatus SecItemDelete(CFDictionaryRef query)

NSString *accessGroup = [NSString stringWithUTF8String:"APPIdentifier.com.cnblogs.smileEvday"];
    if (accessGroup != nil)
    {
#if TARGET_IPHONE_SIMULATOR
        // Ignore the access group if running on the iPhone simulator.
        //
        // Apps that are built for the simulator aren't signed, so there's no keychain access group
        // for the simulator to check. This means that all apps can see all keychain items when run
        // on the simulator.
        //
        // If a SecItem contains an access group attribute, SecItemAdd and SecItemUpdate on the
        // simulator will return -25243 (errSecNoAccessForItem).
#else
        [dictForQuery setObject:accessGroup forKey:(id)kSecAttrAccessGroup];
#endif
    }

+ (BOOL)settUDIDToKeyChain:(NSString*)udid
{
    NSMutableDictionary *dictForAdd = [[NSMutableDictionary alloc] init];
    
    [dictForAdd setValue:(id)kSecClassGenericPassword forKey:(id)kSecClass];
    [dictForAdd setValue:[NSString stringWithUTF8String:kKeychainUDIDItemIdentifier] forKey:kSecAttrDescription];
    
    [dictForAdd setValue:@"UUID" forKey:(id)kSecAttrGeneric];
    
    // Default attributes for keychain item.
    [dictForAdd setObject:@"" forKey:(id)kSecAttrAccount];
    [dictForAdd setObject:@"" forKey:(id)kSecAttrLabel];
    
    // The keychain access group attribute determines if this item can be shared
    // amongst multiple apps whose code signing entitlements contain the same keychain access group.
    NSString *accessGroup = [NSString stringWithUTF8String:kKeyChainUDIDAccessGroup];
    if (accessGroup != nil)
    {
#if TARGET_IPHONE_SIMULATOR
        // Ignore the access group if running on the iPhone simulator.
        //
        // Apps that are built for the simulator aren't signed, so there's no keychain access group
        // for the simulator to check. This means that all apps can see all keychain items when run
        // on the simulator.
        //
        // If a SecItem contains an access group attribute, SecItemAdd and SecItemUpdate on the
        // simulator will return -25243 (errSecNoAccessForItem).
#else
        [dictForAdd setObject:accessGroup forKey:(id)kSecAttrAccessGroup];
#endif
    }

    const char *udidStr = [udid UTF8String];
    NSData *keyChainItemValue = [NSData dataWithBytes:udidStr length:strlen(udidStr)];
    [dictForAdd setValue:keyChainItemValue forKey:(id)kSecValueData];
    
    OSStatus writeErr = noErr;
    if ([SvUDIDTools getUDIDFromKeyChain]) {        // there is item in keychain
        [SvUDIDTools updateUDIDInKeyChain:udid];
        [dictForAdd release];
        return YES;
    }
    else {          // add item to keychain
        writeErr = SecItemAdd((CFDictionaryRef)dictForAdd, NULL);
        if (writeErr != errSecSuccess) {
            NSLog(@"Add KeyChain Item Error!!! Error Code:%ld", writeErr);
            
            [dictForAdd release];
            return NO;
        }
        else {
            NSLog(@"Add KeyChain Item Success!!!");
            [dictForAdd release];
            return YES;
        }
    }
    
    [dictForAdd release];
    return NO;
}

+ (NSString*)getUDIDFromKeyChain
{
    NSMutableDictionary *dictForQuery = [[NSMutableDictionary alloc] init];
    [dictForQuery setValue:(id)kSecClassGenericPassword forKey:(id)kSecClass];
    
    // set Attr Description for query
    [dictForQuery setValue:[NSString stringWithUTF8String:kKeychainUDIDItemIdentifier]
                    forKey:kSecAttrDescription];
    
    // set Attr Identity for query
    NSData *keychainItemID = [NSData dataWithBytes:kKeychainUDIDItemIdentifier
                                            length:strlen(kKeychainUDIDItemIdentifier)];
    [dictForQuery setObject:keychainItemID forKey:(id)kSecAttrGeneric];
    
    // The keychain access group attribute determines if this item can be shared
    // amongst multiple apps whose code signing entitlements contain the same keychain access group.
    NSString *accessGroup = [NSString stringWithUTF8String:kKeyChainUDIDAccessGroup];
    if (accessGroup != nil)
    {
#if TARGET_IPHONE_SIMULATOR
        // Ignore the access group if running on the iPhone simulator.
        //
        // Apps that are built for the simulator aren't signed, so there's no keychain access group
        // for the simulator to check. This means that all apps can see all keychain items when run
        // on the simulator.
        //
        // If a SecItem contains an access group attribute, SecItemAdd and SecItemUpdate on the
        // simulator will return -25243 (errSecNoAccessForItem).
#else
        [dictForQuery setObject:accessGroup forKey:(id)kSecAttrAccessGroup];
#endif
    }
    
    [dictForQuery setValue:(id)kCFBooleanTrue forKey:(id)kSecMatchCaseInsensitive];
    [dictForQuery setValue:(id)kSecMatchLimitOne forKey:(id)kSecMatchLimit];
    [dictForQuery setValue:(id)kCFBooleanTrue forKey:(id)kSecReturnData];
    
    OSStatus queryErr   = noErr;
    NSData   *udidValue = nil;
    NSString *udid      = nil;
    queryErr = SecItemCopyMatching((CFDictionaryRef)dictForQuery, (CFTypeRef*)&udidValue);
    
    NSMutableDictionary *dict = nil;
    [dictForQuery setValue:(id)kCFBooleanTrue forKey:(id)kSecReturnAttributes];
    queryErr = SecItemCopyMatching((CFDictionaryRef)dictForQuery, (CFTypeRef*)&dict);
    
    if (queryErr == errSecItemNotFound) {
        NSLog(@"KeyChain Item: %@ not found!!!", [NSString stringWithUTF8String:kKeychainUDIDItemIdentifier]);
    }
    else if (queryErr != errSecSuccess) {
        NSLog(@"KeyChain Item query Error!!! Error code:%ld", queryErr);
    }
    if (queryErr == errSecSuccess) {
        NSLog(@"KeyChain Item: %@", udidValue);
        
        if (udidValue) {
            udid = [NSString stringWithUTF8String:udidValue.bytes];
        }
    }
    
    [dictForQuery release];
    return udid;
}