iOS的keychain服务提供了一种安全的保存私密信息（密码，序列号，证书等）的方式，每个iOS程序都有一个独立的keychain存储。相对于NSUserDefaults、文件保存等一般方式，keychain保存更为安全，而且keychain里保存的信息不会因App被删除而丢失，所以在重装App后，keychain里的数据还能使用。

在应用里使用使用keyChain，我们需要导入Security.framework

#pragma mark--获取设备UUID
-(NSString*) uuid {if ([CHKeychain load:UUIDKEY]) {NSString *result = [CHKeychain load:UUIDKEY];return result;}else{CFUUIDRef puuid = CFUUIDCreate( nil );CFStringRef uuidString = CFUUIDCreateString( nil, puuid );NSString * result = (NSString *)CFStringCreateCopy( NULL, uuidString);CFRelease(puuid);CFRelease(uuidString);[CHKeychain save:UUIDKEY data:result];return [result autorelease];}return nil;
}

#import <Foundation/Foundation.h>@interface CHKeychain : NSObject+ (void)save:(NSString *)service data:(id)data;
+ (id)load:(NSString *)service;
+ (void)deleteData:(NSString *)service;@end

#import "CHKeychain.h"@implementation CHKeychain
+ (NSMutableDictionary *)getKeychainQuery:(NSString *)service {return [NSMutableDictionary dictionaryWithObjectsAndKeys:(id)kSecClassGenericPassword,(id)kSecClass,service, (id)kSecAttrService,service, (id)kSecAttrAccount,(id)kSecAttrAccessibleAfterFirstUnlock,(id)kSecAttrAccessible,nil];
}+ (void)save:(NSString *)service data:(id)data {//Get search dictionaryNSMutableDictionary *keychainQuery = [self getKeychainQuery:service];//Delete old item before add new itemSecItemDelete((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 dictionarySecItemAdd((CFDictionaryRef)keychainQuery, NULL);
}+ (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;
}+ (void)delete:(NSString *)service {NSMutableDictionary *keychainQuery = [self getKeychainQuery:service];SecItemDelete((CFDictionaryRef)keychainQuery);
}@end