你會如何存儲用戶的一些敏感信息，如登錄的token

使用keychain來存儲,也就是鑰匙串,使用keychain需要導入Security框架

iOS的keychain服務提供了一種安全的保存私密信息（密碼，序列號，證書等）的方式，每個ios程序都有一個獨立的keychain存儲。相對於 NSUserDefaults、文件保存等一般方式，keychain保存更爲安全，而且keychain裏保存的信息不會因App被刪除而丟失，所以在 重裝App後，keychain裏的數據還能使用。從ios 3。0開始，跨程序分享keychain變得可行。

如何需要在應用裏使 用使用keyChain，我們需要導入Security.framework ，keychain的操作接口聲明在頭文件SecItem.h裏。直接使用SecItem.h裏方法操作keychain，需要寫的代碼較爲複雜，爲減輕 咱們程序員的開發，我們可以使用一些已經封裝好了的工具類，下面我會簡單介紹下我用過的兩個工具類：KeychainItemWrapper和 SFHFKeychainUtils。

自定義一個keychain的類

• CSKeyChain.h

@interface CSKeyChain : NSObject

+ (NSMutableDictionary *)getKeychainQuery:(NSString *)service;

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

+ (id)load:(NSString *)service;

+ (void)delete:(NSString *)service;

@end

• CSKeyChain.m

#import "CSKeyChain.h"
#import<Security/Security.h>

@implementation CSKeyChain

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

+ (void)save:(NSString *)service data:(id)data {
    // 獲得搜索字典
    NSMutableDictionary *keychainQuery = [self getKeychainQuery:service];
    // 添加新的刪除舊的
    SecItemDelete((__bridge_retained CFDictionaryRef)keychainQuery);
    // 添加新的對象到字符串
    [keychainQuery setObject:[NSKeyedArchiver archivedDataWithRootObject:data] forKey:(__bridge_transfer id)kSecValueData];
    // 查詢鑰匙串
    SecItemAdd((__bridge_retained CFDictionaryRef)keychainQuery, NULL);
}

+ (id)load:(NSString *)service {
    id ret = nil;
    NSMutableDictionary *keychainQuery = [self getKeychainQuery:service];
    // 配置搜索設置
    [keychainQuery setObject:(id)kCFBooleanTrue forKey:(__bridge_transfer id)kSecReturnData];
    [keychainQuery setObject:(__bridge_transfer id)kSecMatchLimitOne forKey:(__bridge_transfer id)kSecMatchLimit];
    
    CFDataRef keyData = NULL;
    
    if (SecItemCopyMatching((__bridge_retained CFDictionaryRef)keychainQuery, (CFTypeRef *)&keyData) == noErr) {
        @try {
            ret = [NSKeyedUnarchiver unarchiveObjectWithData:(__bridge_transfer NSData *)keyData];
        } @catch (NSException *e) {
            NSLog(@"Unarchive of %@ failed: %@", service, e);
        } @finally {
        }
    }
    
    return ret;
}

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

@end

• 在別的類實現存儲,加載,刪除敏感信息方法

// 用來標識這個鑰匙串
static NSString * const KEY_IN_KEYCHAIN = @"com.cs.app.allinfo";
// 用來標識密碼
static NSString * const KEY_PASSWORD = @"com.cs.app.password";

+ (void)savePassWord:(NSString *)password {
    NSMutableDictionary *passwordDict = [NSMutableDictionary dictionary];
    [passwordDict setObject:password forKey:KEY_PASSWORD];
    [CSKeyChain save:KEY_IN_KEYCHAIN data:passwordDict];
}

+ (id)readPassWord {
    NSMutableDictionary *passwordDict = (NSMutableDictionary *)[CSKeyChain load:KEY_IN_KEYCHAIN];
    return [passwordDict objectForKey:KEY_PASSWORD];
}

+ (void)deletePassWord {
    [CSKeyChain delete:KEY_IN_KEYCHAIN];
}

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原文更多：iOS面試題大全