IOS开发模块总结（一）本地数据存储6 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>

@interface CHKeychain : NSObject

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

@end

CHKeychain.m

#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 dictionary
NSMutableDictionary *keychainQuery = [self getKeychainQuery:service];
//Delete old item before add new item
SecItemDelete((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 dictionary
SecItemAdd((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

首先需要定义几个字符串用来做key：

NSString * const KEY_USERNAME_PASSWORD = @"com.company.app.usernamepassword";
NSString * const KEY_USERNAME = @"com.company.app.username";
NSString * const KEY_PASSWORD = @"com.company.app.password";

把用户名和密码存入keychain：

NSMutableDictionary *usernamepasswordKVPairs = [NSMutableDictionary dictionary];
[usernamepasswordKVPairs setObject:txtfldUsername.text forKey:KEY_USERNAME];
[usernamepasswordKVPairs setObject:txtfldPassword.text forKey:KEY_PASSWORD];
[CHKeychain save:KEY_USERNAME_PASSWORD data:usernamepasswordKVPairs];

从keychain中取出用户名和密码：

NSMutableDictionary *usernamepasswordKVPairs = (NSMutableDictionary *)[CHKeychain load:KEY_USERNAME_PASSWORD];
txtfldUsername.text = [usernamepasswordKVPairs objectForKey:KEY_USERNAME];
txtfldPassword.text = [usernamepasswordKVPairs objectForKey:KEY_PASSWORD];

删除一个keychain item:

[CHKeychain delete:KEY_USERNAME_PASSWORD];

另外在使用系统的KeychainItemWrapper文件时，更改identify后保存用户名密会失败。解决办法http://stackoverflow.com/questions/4891562/ios-keychain-services-only-specific-values-allowed-for-ksecattrgeneric-key