1.新建一个LYKeychainTool类，导入系统Security框架 ，LYKeychainTool.h文件实现如下：

//
//  LYKeychainTool.h
//  keyChainTest
//
//  Created by Liyu on 2017/6/2.
//  Copyright © 2017年 liyu. All rights reserved.
//

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

@interface LYKeychainTool : NSObject

/**
 *  储存字符串到钥匙串
 *  @param sValue 对应的Value
 *  @param sKey   对应的Key
 */
+ (void)saveKeychainValue:(NSString *)sValue key:(NSString *)sKey;

/**
 *  从钥匙串获取字符串
 *  @param sKey 对应的Key
 *  @return 返回储存的Value
 */
+ (NSString *)readKeychainValue:(NSString *)sKey;

/**
 *  从钥匙串删除字符串
 *  @param sKey 对应的Key
 */
+ (void)deleteKeychainValue:(NSString *)sKey;

@end

2.LYKeychainTool.m文件实现如下：

//
//  LYKeychainTool.m
//  keyChainTest
//
//  Created by Liyu on 2017/6/2.
//  Copyright © 2017年 liyu. All rights reserved.
//

#import "LYKeychainTool.h"

@implementation LYKeychainTool

+ (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)saveKeychainValue:(NSString *)sValue key:(NSString *)sKey {
    NSMutableDictionary * keychainQuery = [self getKeychainQuery:sKey];
    SecItemDelete((__bridge_retained CFDictionaryRef)keychainQuery);
    [keychainQuery setObject:[NSKeyedArchiver archivedDataWithRootObject:sValue] forKey:(__bridge_transfer id)kSecValueData];
    SecItemAdd((__bridge_retained CFDictionaryRef)keychainQuery, NULL);
}

+ (NSString *)readKeychainValue:(NSString *)sKey {
    NSString *ret = nil;
    NSMutableDictionary *keychainQuery = [self getKeychainQuery:sKey];
    [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 CFDictionaryRef)keychainQuery, (CFTypeRef *)&keyData) == noErr) {
        @try {
            ret = (NSString *)[NSKeyedUnarchiver unarchiveObjectWithData:(__bridge NSData *)keyData];
        } @catch (NSException *e) {
            NSLog(@"Unarchive of %@ failed: %@", sKey, e);
        } @finally {
        }
    }
    if (keyData)
        CFRelease(keyData);
    return ret;
}

+ (void)deleteKeychainValue:(NSString *)sKey {
    NSMutableDictionary *keychainQuery = [self getKeychainQuery:sKey];
    SecItemDelete((__bridge CFDictionaryRef)keychainQuery);
}

@end

3.ViewController 调用

//
//  ViewController.m
//  keyChainTest
//
//  Created by Liyu on 2017/6/2.
//  Copyright © 2017年 liyu. All rights reserved.
//

#import "ViewController.h"
#import "LYKeychainTool.h"

@interface ViewController ()

@property (weak, nonatomic) IBOutlet UITextField *userNameTextField;

@property (weak, nonatomic) IBOutlet UITextField *passwordTextField;

@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];

}

- (IBAction)saveBtn:(id)sender {
    [LYKeychainTool saveKeychainValue:self.userNameTextField.text key:@"userName"];
    [LYKeychainTool saveKeychainValue:self.passwordTextField.text key:@"password"];
}

- (IBAction)readeBtn:(id)sender {
    self.userNameTextField.text = [NSString stringWithFormat:@"读取到用户名:%@",[LYKeychainTool readKeychainValue:@"userName"]];
    self.passwordTextField.text = [NSString stringWithFormat:@"读取到用户密码:%@",[LYKeychainTool readKeychainValue:@"password"]];
}

- (IBAction)deleteBtn:(id)sender {
    [LYKeychainTool deleteKeychainValue:@"userName"];
    [LYKeychainTool deleteKeychainValue:@"password"];
}

- (void)didReceiveMemoryWarning {
    [super didReceiveMemoryWarning];

}


@end

4.效果如下图：

图