前言
获取设备唯一标识符，开发者大脑里产生的第一方案就是获取设备MAC地址，遗憾的是苹果iOS7之后获取到的mac是固定值，因此在通过MAC地址充当唯一标识此路不通；苹果iOS6另外一个新的方法（IDFA），提供了一个方法advertisingIdentifier，通过调用该方法会返回一个NSUUID实例，最后可以获得一个UUID，由系统存储着的，由于IDFA会出现取不到的情况，故绝不可以作为设备唯一标识符。还有IDFV(identifierForVendor)，应用提供商标识符，如果用户将属于此Vender的所有App卸载，则IDFV的值会被重置，即再重装此Vender的App，IDFV的值和之前不同，因此想通过IDFV作为设备唯一标识符，需要KeyChain配合（KeyChain的优缺点）本文不阐述。
1、结构设计方案（KeyChain+IDFV）
（1）创建一个共用的KeyChain（钥匙串）的管理对象，负责对KeyChain中Item的增删改查以及Item是否App之间共享等等；
（2）然后根据需求二次封装，不管你要保存UUID还是账户密码，你需要做的就是创建特定的广利对象（比如说下文的XPQKeychainUUID用于管理UUID）封装相应的存储逻辑，最后通过XPQKeychainManager写入KeyChain。
#import@interface XPQKeychainManager : NSObject- (instancetype)initSecAttrAccessGroup:(NSString *)secAttrAccessGroup;- (id)secValueDataForService:(NSString *)aService;- (id)secValueDataForService:(NSString *)aService account:(NSString *)account;- (BOOL)saveKeychainData:(id)data service:(NSString *)aService;- (BOOL)saveKeychainData:(id)data service:(NSString *)aService account:(NSString *)account;- (BOOL)deleteKeychainDataForService:(NSString *)aService;- (BOOL)deleteKeychainDataForService:(NSString *)aService account:(NSString *)account;@end#import "XPQKeychainManager.h"@interface XPQKeychainManager ()@property (nonatomic, copy) NSString *secAttrAccessGroup;@end@implementation XPQKeychainManager- (instancetype)init{ return [self initSecAttrAccessGroup:nil];}- (instancetype)initSecAttrAccessGroup:(NSString *)secAttrAccessGroup{ self = [super init]; if (self) { self.secAttrAccessGroup = secAttrAccessGroup; } return self;}- (NSMutableDictionary *)queryKeychainForService:(NSString *)aService account:(NSString *)account{ return [NSMutableDictionary dictionaryWithObjectsAndKeys: (__bridge id)kSecClassGenericPassword,(__bridge_transfer id)kSecClass, aService, (__bridge_transfer id)kSecAttrService, account, (__bridge_transfer id)kSecAttrAccount, (__bridge id)kSecAttrAccessibleAfterFirstUnlock,(__bridge_transfer id)kSecAttrAccessible, nil];}- (id)secValueDataForService:(NSString *)aService { return [self secValueDataForService:aService account:aService];}- (id)secValueDataForService:(NSString *)aService account:(NSString *)account{ if (!aService && !account) { return nil; } NSMutableDictionary *keychainQuery = [self queryKeychainForService:aService account:account]; if (self.secAttrAccessGroup) { [keychainQuery setObject:self.secAttrAccessGroup forKey:(__bridge_transfer id)kSecAttrAccessGroup]; } NSMutableDictionary *attributeQuery = [keychainQuery mutableCopy]; [attributeQuery setObject:(id)kCFBooleanTrue forKey:(__bridge_transfer id)kSecReturnAttributes]; CFTypeRef attrResult = NULL; OSStatus status = SecItemCopyMatching(((__bridge_retained CFDictionaryRef)attributeQuery), (CFTypeRef *)&attrResult); if (status != noErr) { return nil; } NSMutableDictionary *secValueDataQuery = [keychainQuery mutableCopy]; [secValueDataQuery setObject:(id)kCFBooleanTrue forKey:(__bridge_transfer id)kSecReturnData]; CFTypeRef resData = NULL; status = SecItemCopyMatching(((__bridge_retained CFDictionaryRef)secValueDataQuery), (CFTypeRef *)&resData); NSData *resultData = (__bridge_transfer NSData *)resData; if (status != noErr) { return nil; } return resultData ? [NSKeyedUnarchiver unarchiveObjectWithData:resultData] : nil;}- (BOOL)saveKeychainData:(id)data service:(NSString *)aService { return [self saveKeychainData:data service:aService account:aService];}- (BOOL)saveKeychainData:(id)data service:(NSString *)aService account:(NSString *)account{ if (!aService && !account) { return NO; } NSMutableDictionary *keychainQuery = [self queryKeychainForService:aService account:account]; if (self.secAttrAccessGroup) { [keychainQuery setObject:self.secAttrAccessGroup forKey:(__bridge_transfer id)kSecAttrAccessGroup]; } id keychainData = [self secValueDataForService:aService account:account]; OSStatus status = noErr; if (keychainData) { NSMutableDictionary *updateKeychainData = [keychainQuery mutableCopy]; if (![keychainData isEqualToString:data]) { NSMutableDictionary *tempCheck = [NSMutableDictionary dictionaryWithObject:[NSKeyedArchiver archivedDataWithRootObject:data] forKey:(__bridge_transfer id)kSecValueData]; status = SecItemUpdate(((__bridge_retained CFDictionaryRef)updateKeychainData), (__bridge_retained CFDictionaryRef)tempCheck); } } else { NSMutableDictionary *addKeychainData = [keychainQuery mutableCopy]; [addKeychainData setObject:[NSKeyedArchiver archivedDataWithRootObject:data] forKey:(__bridge_transfer id)kSecValueData]; status = SecItemAdd(((__bridge_retained CFDictionaryRef)addKeychainData), NULL); } if (status != noErr) { return NO; } return YES;}- (BOOL)deleteKeychainDataForService:(NSString *)aService { return [self deleteKeychainDataForService:aService account:aService];}- (BOOL)deleteKeychainDataForService:(NSString *)aService account:(NSString *)account{ if (!aService && !account) { return NO; } NSMutableDictionary *keychainQuery = [self queryKeychainForService:aService account:account]; OSStatus status = SecItemDelete(((__bridge_retained CFDictionaryRef)keychainQuery)); if (status != noErr) { return NO; } return YES;}@end
2、保存与获取IDFV，关键代码NSString *uuid =
[[UIDevice currentDevice].identifierForVendor UUIDString];#import#import @interface XPQKeychainUUID : NSObject- (id)readUUID;- (BOOL)deleteItem;@end#import "XPQKeychainUUID.h"#import "XPQKeychainManager.h"@interface XPQKeychainUUID ()@property (nonatomic, copy) NSString *uuid;@property (nonatomic, strong) XPQKeychainManager *keychainManager;@endstatic NSString * const KEY_IN_KEYCHAIN_UUID = @"com.xpq.keychain.uuid";@implementation XPQKeychainUUID- (instancetype)init{ self = [super init]; if (self) { self.keychainManager = [[XPQKeychainManager alloc] init]; } return self;}- (BOOL)save:(id)data service:(NSString *)service { return [self.keychainManager saveKeychainData:data service:KEY_IN_KEYCHAIN_UUID];}- (NSString *)getUUID { return [[UIDevice currentDevice].identifierForVendor UUIDString];}- (id)readUUID { if (!_uuid || _uuid.length == 0) { NSString *strUUID = [self load:KEY_IN_KEYCHAIN_UUID]; if (!strUUID || strUUID.length == 0) { strUUID = [self getUUID]; [self save:strUUID]; } _uuid = strUUID; } return _uuid;}- (id)load:(NSString *)service { return [self.keychainManager secValueDataForService:KEY_IN_KEYCHAIN_UUID];}- (BOOL)save:(id)data { return [self save:data service:KEY_IN_KEYCHAIN_UUID];}- (BOOL)deleteItem { return [self.keychainManager deleteKeychainDataForService:KEY_IN_KEYCHAIN_UUID];}@end
总结
Keychain内部的数据会自动加密。如果设备没有越狱并且不暴力破解，keychain确实很安全。但是越狱后的设备，keychain就很危险了，因此还需要对重要信息进行加密处理再放入Keychain。