keychain使用介绍

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。从ios 3.0开始，跨程序分享keychain变得可行。

使用苹果官方发布的KeychainItemWrapper或者SFHFKeychainUtils很方便。

苹果已经有现成的类封装好了keychain,KeychainItemWrapper.h和KeychainItemWrapper.m文件,可以在GenericKeychain实例里找到。

下面就使用keychain来实现存取用户名和密码。

代码如下：

CHKeychain.h

#import<Foundation/Foundation.h>
#import<Security/Security.h>


@interfaceCHKeychain:NSObject

+(void)save:(NSString*)servicedata:(id)data;
+(id)load:(NSString*)service;
+(void)delete:(NSString*)service;


@end

CHKeychain.m

#import"CHKeychain.h"

@implementationCHKeychain
+(NSMutableDictionary*)getKeychainQuery:(NSString*)service{
return[NSMutableDictionarydictionaryWithObjectsAndKeys:
(id)kSecClassGenericPassword,(id)kSecClass,
service,(id)kSecAttrService,
service,(id)kSecAttrAccount,
(id)kSecAttrAccessibleAfterFirstUnlock,(id)kSecAttrAccessible,
nil];
}

+(void)save:(NSString*)servicedata:(id)data{
//Getsearchdictionary
NSMutableDictionary*keychainQuery=[selfgetKeychainQuery:service];
//Deleteolditembeforeaddnewitem
SecItemDelete((CFDictionaryRef)keychainQuery);
//Addnewobjecttosearchdictionary(Attention:thedataformat)
[keychainQuerysetObject:[NSKeyedArchiverarchivedDataWithRootObject:data]forKey:(id)kSecValueData];
//Additemtokeychainwiththesearchdictionary
SecItemAdd((CFDictionaryRef)keychainQuery,NULL);
}

+(id)load:(NSString*)service{
idret=nil;
NSMutableDictionary*keychainQuery=[selfgetKeychainQuery:service];
//Configurethesearchsetting
//Sinceinoursimplecaseweareexpectingonlyasingleattributetobereturned(thepassword)wecansettheattributekSecReturnDatatokCFBooleanTrue
[keychainQuerysetObject:(id)kCFBooleanTrueforKey:(id)kSecReturnData];
[keychainQuerysetObject:(id)kSecMatchLimitOneforKey:(id)kSecMatchLimit];
CFDataRefkeyData=NULL;
if(SecItemCopyMatching((CFDictionaryRef)keychainQuery,(CFTypeRef*)&keyData)==noErr){
@try{
ret=[NSKeyedUnarchiverunarchiveObjectWithData:(NSData*)keyData];
}@catch(NSException*e){
NSLog(@"Unarchiveof%@failed:%@",service,e);
}@finally{
}
}
if(keyData)
CFRelease(keyData);
returnret;
}

+(void)delete:(NSString*)service{
NSMutableDictionary*keychainQuery=[selfgetKeychainQuery:service];
SecItemDelete((CFDictionaryRef)keychainQuery);
}


@end

首先需要定义几个字符串用来做key：

NSString*constKEY_USERNAME_PASSWORD=@"com.company.app.usernamepassword";
NSString*constKEY_USERNAME=@"com.company.app.username";
NSString*constKEY_PASSWORD=@"com.company.app.password";

把用户名和密码存入keychain：

NSMutableDictionary*usernamepasswordKVPairs=[NSMutableDictionarydictionary];
[usernamepasswordKVPairssetObject:txtfldUsername.textforKey:KEY_USERNAME];
[usernamepasswordKVPairssetObject:txtfldPassword.textforKey:KEY_PASSWORD];
[CHKeychainsave:KEY_USERNAME_PASSWORDdata:usernamepasswordKVPairs];

从keychain中取出用户名和密码：

NSMutableDictionary*usernamepasswordKVPairs=(NSMutableDictionary*)[CHKeychainload:KEY_USERNAME_PASSWORD];
txtfldUsername.text=[usernamepasswordKVPairsobjectForKey:KEY_USERNAME];
txtfldPassword.text=[usernamepasswordKVPairsobjectForKey:KEY_PASSWORD];

删除一个keychain item:

[CHKeychaindelete:KEY_USERNAME_PASSWORD];

这样一个简单的使用keychain存取用户名密码的功能就做好了。

另外附上一篇写得更详细的e文：http://useyourloaf.com/blog/2010/3/29/simple-iphone-keychain-access.html