iOS KeyChain使用

最近項目需要存儲用戶的唯一標識符，但是由於如果用戶重裝APP，獲取到的又會是一個新的UDID。查詢了一系列資料下來，可以用Keychain進行存儲UDID，然後就算重裝了APP，也能從Keychain中讀取出之前存儲的UDID。

Keychain存儲在iOS系統的內部數據庫中,由系統進行管理和加密，哪怕APP被刪除了，它存儲在Keychain中的數據也不會被刪除。

So，Keychain使用走起～
首先一定要在Capabilities中打開Keychain，如圖：

6B836BEE-1CDC-4D49-8E7E-50490DE2E953.png

好吧，不打開的話進行Keychain操作將會返回一個34018的錯誤碼。。

當然別忘記引入import <Security/Security.h>

Keychain存儲的流程如圖所示：

B9C180AB-88D0-44B6-905E-37802CC13B6E.png

簡單來說，如果要存儲一個password，需要先遍歷Keychain，看它的password是否已經存在於Keychain中，存在的話就更新它的值，不存在就存儲。
所以這就使用到蘋果提供的方法：

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

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

// 更新
OSStatus SecItemUpdate(CFDictionaryRef query, CFDictionaryRef attributesToUpdate);

// 刪除
OSStatus SecItemDelete(CFDictionaryRef query)

接下來看看操作Keychain常用的key-value.

kSecClass:有五個值，分別爲
      kSecClassGenericPassword(通用密碼－－也是接下來使用的)、
      kSecClassInternetPassword(互聯網密碼)、
      kSecClassCertificate(證書)、
      kSecClassKey(密鑰)、
      kSecClassIdentity(身份)

kSecAttrService:服務
kSecAttrServer:服務器域名或IP地址
kSecAttrAccount:賬號
kSecAttrAccessGroup: 可以在應用之間共享keychain中的數據
kSecMatchLimit:返回搜索結果，kSecMatchLimitOne（一個）、kSecMatchLimitAll（全部）
//

這是基於CoreFundation框架的操作，通過帶有以上key－value值的字典進行操作，所以寫起來還是有些繁瑣的。所幸蘋果提供了一個源碼Demo。demo中使用service和account以及accessGroup進行password的存儲，也就是一個kSecClassGenericPassword類型的Keychain表，一個account對應一個password，可以很方便在APP中進行Key-Value類型的存儲。

不過由於它是使用Swift編寫的，在我的小項目中不適合引入混編，所以我就按着demo 的邏輯抄了個OC版的出來。個人看來，OC的還是好懂點，去除了各種try catch，思路上會清晰很多。

初始化方法：

- (instancetype)initWithSevice:(NSString *)service account :(NSString *)account accessGroup:(NSString *)accessGroup {
    if (self = [super init]) {
        _service = service;
        _account = account;
        _accessGroup = accessGroup;//可以在不同的app當中共享
    }
    return self;
}

主要方法有：

- (void)savePassword:(NSString *)password;
- (BOOL)deleteItem;

- (NSString *)readPassword;

//返回當前accessGroup下的service的所有Keychain Item
+ (NSArray *)passwordItemsForService:(NSString *)service accessGroup:(NSString *)accessGroup;

（具體代碼在後面貼吧，防止影響篇幅，有興趣的朋友也可以下demo看看）

使用起來就是：
存儲：

    KeychainWrapper *wrapper = [[KeychainWrapper alloc] initWithSevice:kKeychainService account:self.accountField.text accessGroup:kKeychainAccessGroup];
    [wrapper savePassword:self.passwordField.text];

讀取當前account 的password：

KeychainWrapper *item = [[KeychainWrapper alloc] initWithSevice:service account:acount accessGroup:accessGroup];
[item readPassword];

返回當前accessGroup下的service的所有Keychain：

NSArray *keychains = [KeychainWrapper passwordItemsForService:kKeychainService accessGroup:kKeychainAccessGroup];

踩坑：OSStatus狀態錯誤碼：

• 50: 請求參數錯誤。我就曾經把kSecAttrService寫成了kSecAttrServer，crash到哭了。。。
• 34018:前面說的Capabilities…

代碼：

- (void)savePassword:(NSString *)password {
    NSData *encodePasswordData = [password dataUsingEncoding:NSUTF8StringEncoding];

    // if password was existed, update
    NSString *originPassword = [self readPassword];

    if (originPassword.length > 0) {
        NSMutableDictionary *updateAttributes = [NSMutableDictionary dictionary];
        updateAttributes[(__bridge id)kSecValueData] = encodePasswordData;

        NSMutableDictionary *query = [self keychainQueryWithService:_service account:_account accessGroup:_accessGroup];
        OSStatus statusCode = SecItemUpdate(
                                           (__bridge CFDictionaryRef)query,
                                           (__bridge CFDictionaryRef)updateAttributes);
        NSAssert(statusCode == noErr, @"Couldn't update the Keychain Item." );
    }else{
        // else , add
        NSMutableDictionary *attributes = [self keychainQueryWithService:_service account:_account accessGroup:_accessGroup];
        attributes[(__bridge id)kSecValueData] = encodePasswordData;

        OSStatus status = SecItemAdd((__bridge CFDictionaryRef)attributes, nil);

        NSAssert(status == noErr, @"Couldn't add the Keychain Item.");
    }
}

- (NSString *)readPassword {
    NSMutableDictionary *attributes = [self keychainQueryWithService:_service account:_account accessGroup:_accessGroup];
    attributes[(__bridge id)kSecMatchLimit] = (__bridge id)(kSecMatchLimitOne);
    attributes[(__bridge id)kSecReturnAttributes] = (__bridge id _Nullable)(kCFBooleanTrue);
    attributes[(__bridge id)kSecReturnData] = (__bridge id _Nullable)(kCFBooleanTrue);

    CFMutableDictionaryRef queryResult = nil;
    OSStatus keychainError = noErr;
    keychainError = SecItemCopyMatching((__bridge CFDictionaryRef)attributes,(CFTypeRef *)&queryResult);
    if (keychainError == errSecItemNotFound) {
        if (queryResult) CFRelease(queryResult);
        return nil;
    }else if (keychainError == noErr) {

        if (queryResult == nil){return nil;}

        NSMutableDictionary *resultDict = (__bridge NSMutableDictionary *)queryResult;
        NSData *passwordData = resultDict[(__bridge id)kSecValueData];

        NSString *password = [[NSString alloc] initWithData:passwordData encoding:NSUTF8StringEncoding];

        return password;
    }else
    {
        NSAssert(NO, @"Serious error.\n");
        if (queryResult) CFRelease(queryResult);
    }

    return nil;
}

- (NSMutableDictionary *)keychainQueryWithService:(NSString *)service account:(NSString *)account accessGroup:(NSString *)accessGroup {

    NSMutableDictionary *query = [NSMutableDictionary dictionary];

    query[(__bridge id)kSecClass] = (__bridge id)kSecClassGenericPassword;

    query[(__bridge id)kSecAttrService] = service;

    query[(__bridge id)kSecAttrAccount] = account;

    query[(__bridge id)kSecAttrAccessGroup] = accessGroup;

    return query;
}

+ (NSArray *)passwordItemsForService:(NSString *)service accessGroup:(NSString *)accessGroup {
    NSMutableDictionary *query = [[[self alloc]init] keychainQueryWithService:service account:nil accessGroup:accessGroup];

    query[(__bridge id)kSecMatchLimit] = (__bridge id)kSecMatchLimitAll;
    query[(__bridge id)kSecReturnAttributes] = (__bridge id _Nullable)(kCFBooleanTrue);
    query[(__bridge id)kSecReturnData] = (__bridge id _Nullable)(kCFBooleanFalse);

    CFMutableArrayRef queryResult = nil;
    OSStatus status = noErr;
    status = SecItemCopyMatching((__bridge CFDictionaryRef)query,(CFTypeRef *)&queryResult);

    if (status == errSecItemNotFound) {
        return @[];
    }else if (status == noErr) {

        NSArray<NSDictionary *> *resultArray = (__bridge NSArray<NSDictionary *> *)queryResult;

        if (resultArray.count == 0){return @[];}

        NSMutableArray *passwordItems = [NSMutableArray array];

        for (NSDictionary *result in resultArray) {
            NSString *acount = result[(__bridge id)kSecAttrAccount];

            if (acount.length > 0) {
                KeychainWrapper *item = [[KeychainWrapper alloc] initWithSevice:service account:acount accessGroup:accessGroup];
                [passwordItems addObject:item];
            }
        }

        return passwordItems;
    }else {
        NSAssert(NO, @"Serious error.\n");
        if (queryResult) CFRelease(queryResult);
        return @[];
    }
}

- (BOOL)deleteItem {
    // Delete the existing item from the keychain.
    NSMutableDictionary *query = [self keychainQueryWithService:self.service account:self.account accessGroup:self.accessGroup];

    OSStatus status = SecItemDelete((__bridge CFDictionaryRef)query);

    if (status != noErr && status != errSecItemNotFound) {
        return NO;
    }
    return true;
}

demo
參考：
https://developer.apple.com/library/prerelease/content/documentation/Security/Conceptual/keychainServConcepts/iPhoneTasks/iPhoneTasks.html#//apple_ref/doc/uid/TP30000897-CH208-SW1
http://www.360doc.com/content/15/0708/15/20918780_483580050.shtml
https://my.oschina.net/w11h22j33/blog/206713