最近项目需要存储用户的唯一标识符，但是由于如果用户重装APP，获取到的又会是一个新的UDID。查询了一系列资料下来，可以用Keychain进行存储UDID，然后就算重装了APP，也能从Keychain中读取出之前存储的UDID。
Keychain存储在iOS系统的内部数据库中,由系统进行管理和加密，哪怕APP被删除了，它存储在Keychain中的数据也不会被删除。
So，Keychain使用走起～
首先一定要在Capabilities中打开Keychain，如图：
6B836BEE-1CDC-4D49-8E7E-50490DE2E953.png
好吧，不打开的话进行Keychain操作将会返回一个34018的错误码。。
当然别忘记引入import <Security/Security.h>
Keychain存储的流程如图所示：
B9C180AB-88D0-44B6-905E-37802CC13B6E.png
简单来说，如果要存储一个password，需要先遍历Keychain，看它的password是否已经存在于Keychain中，存在的话就更新它的值，不存在就存储。
所以这就使用到苹果提供的方法：
// 查询
OSStatus SecItemCopyMatching(CFDictionaryRef query, CFTypeRef *result);
// 添加
OSStatus SecItemAdd(CFDictionaryRef attributes, CFTypeRef *result);
// 更新
OSStatus SecItemUpdate(CFDictionaryRef query, CFDictionaryRef attributesToUpdate);
// 删除
OSStatus SecItemDelete(CFDictionaryRef query)
接下来看看操作Keychain常用的key-value.
kSecClass:有五个值，分别为
kSecClassGenericPassword(通用密码－－也是接下来使用的)、
kSecClassInternetPassword(互联网密码)、
kSecClassCertificate(证书)、
kSecClassKey(密钥)、
kSecClassIdentity(身份)
kSecAttrService:服务
kSecAttrServer:服务器域名或IP地址
kSecAttrAccount:账号
kSecAttrAccessGroup: 可以在应用之间共享keychain中的数据
kSecMatchLimit:返回搜索结果，kSecMatchLimitOne（一个）、kSecMatchLimitAll（全部）
//
这是基于CoreFundation框架的操作，通过带有以上key－value值的字典进行操作，所以写起来还是有些繁琐的。所幸苹果提供了一个源码Demo。demo中使用service和account以及accessGroup进行password的存储，也就是一个kSecClassGenericPassword类型的Keychain表，一个account对应一个password，可以很方便在APP中进行Key-Value类型的存储。
不过由于它是使用Swift编写的，在我的小项目中不适合引入混编，所以我就按着demo 的逻辑抄了个OC版的出来。个人看来，OC的还是好懂点，去除了各种try catch，思路上会清晰很多。
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当中共享
}
return self;
}
主要方法有：
- (void)savePassword:(NSString *)password;
- (BOOL)deleteItem;
- (NSString *)readPassword;
//返回当前accessGroup下的service的所有Keychain Item
+ (NSArray *)passwordItemsForService:(NSString *)service accessGroup:(NSString *)accessGroup;
（具体代码在后面贴吧，防止影响篇幅，有兴趣的朋友也可以下demo看看）
使用起来就是：
存储：
KeychainWrapper *wrapper = [[KeychainWrapper alloc] initWithSevice:kKeychainService account:self.accountField.text accessGroup:kKeychainAccessGroup];
[wrapper savePassword:self.passwordField.text];
读取当前account 的password：
KeychainWrapper *item = [[KeychainWrapper alloc] initWithSevice:service account:acount accessGroup:accessGroup];
[item readPassword];
返回当前accessGroup下的service的所有Keychain：
NSArray *keychains = [KeychainWrapper passwordItemsForService:kKeychainService accessGroup:kKeychainAccessGroup];
踩坑：OSStatus状态错误码：
- 50: 请求参数错误。我就曾经把kSecAttrService写成了kSecAttrServer，crash到哭了。。。
- 34018:前面说的Capabilities...
代码：
- (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
参考：
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
