iOS开发，使用keychain保存用户名密码

本文提供完整版demo，源码下载地址：GitHub Demo下载

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>
@interface KeyChain : 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"

@implementation KeyChain

        /**
         *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);
    return ret;
}
#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 * const KEY_USERNAME_PASSWORD = @"com.company.app.usernamepassword";
    NSString * const KEY_USERNAME = @"com.company.app.username";
    NSString * const KEY_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。