KeyChain是苹果提供的一种安全的保存用户名、密码、证书的方式，将敏感信息保存在keychain中后，这些信息不会随着app的卸载而丢失，除非开发人员在app中手动删除敏感信息，否则，这些信息将会一直保存在keychain中。
在使用keychain时，我们首先要将security.framework引入到工程中。由于使用时不支持arc，所以我们在arc环境中需要针对相关文件启用mrc模式。
首先，我们构造一个工具类，通过这个类来操作keychain。
#import<foundation foundation.h="">
#import<security security.h="">
@interfaceKeyChain : NSObject
// save username and password to keychain
+ (void)save:(NSString *)service data:(id)data;
// take out username and passwore from keychain
+ (id)load:(NSString *)service;
// delete username and password from keychain
+ (void)delete:(NSString *)service;
@end
在实现文件中，我们这样写：
#import"KeyChain.h"
@implementationKeyChain
/**
*该类需要工作在mrc模式下，acr的项目按照如下步骤操作
*选中工程->TARGETS->相应的target然后选中右侧的“Build Phases”，向下就找到“Compile Sources”了。然后在相应的文件后面添加:-fno-objc-arc参数
*
**/
+ (NSMutableDictionary *)getKeychainQuery:(NSString *)service {
return[NSMutableDictionary dictionaryWithObjectsAndKeys:
(id)kSecClassGenericPassword,(id)kSecClass,
service, (id)kSecAttrService,
service, (id)kSecAttrAccount,
(id)kSecAttrAccessibleAfterFirstUnlock,(id)kSecAttrAccessible,
nil];
}
#pragma mark 写入
+ (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);
}
#pragma mark 读取
+ (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);
returnret;
}
#pragma mark 删除
+ (void)delete:(NSString *)service {
NSMutableDictionary *keychainQuery = [self getKeychainQuery:service];
SecItemDelete((CFDictionaryRef)keychainQuery);
}
@end
修改工程的相关放在在代码注释中已经写清楚了。
下边是使用这个类
首先，我们定义几个字符串类型的标识符
NSString *constKEY_USERNAME_PASSWORD = @"com.company.app.usernamepassword";
NSString *constKEY_USERNAME = @"com.company.app.username";
NSString *constKEY_PASSWORD = @"com.company.app.password";
之后，我们创建一个字典，并将用户名和密码放入字典中
NSMutableDictionary *userNamePasswordKVPairs = [NSMutableDictionary dictionary];
[userNamePasswordKVPairs setObject:@"userName"forKey:KEY_USERNAME];
[userNamePasswordKVPairs setObject:@"password"forKey:KEY_PASSWORD];
下边引用工具类的各个方法，分别进行用户名和密码的添加、读取、删除操作
// A、将用户名和密码写入keychain
[KeyChain save:KEY_USERNAME_PASSWORD data:userNamePasswordKVPairs];
// B、从keychain中读取用户名和密码
NSMutableDictionary *readUsernamePassword = (NSMutableDictionary *)[KeyChain load:KEY_USERNAME_PASSWORD];
NSString *userName = [readUsernamePassword objectForKey:KEY_USERNAME];
NSString *password = [readUsernamePassword objectForKey:KEY_PASSWORD];
NSLog(@"username = %@", userName);
NSLog(@"password = %@", password);
// C、将用户名和密码从keychain中删除
[KeyChain delete:KEY_USERNAME_PASSWORD];
keychain的用法还有很多，我们在这里只是简单的将用户名和密码保存在keychain，而不是数据库或nsuserdefaults中，以增加安全性。
