iOS 키체인을 위한 헬퍼 클래스 입니다.

KeyChain.h

//
//  KeyChain.h
//  AppGroupProducer
//
//  Created by VIEWPOINT on 2016. 12. 20..
//  Copyright © 2016년 VIEWPOINT. All rights reserved.
//

#ifndef KeyChain_h
#define KeyChain_h

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

// Reference to http://hayageek.com/ios-keychain-tutorial/

@interface KeyChain : NSObject
+ (NSString *)groupIdWithAppIdPrefixWithKey:(NSString *)key;

- (id)initWithService:(NSString *)service_ withGroup:(NSString *)group_;

- (NSMutableDictionary *)prepareDict:(NSString *)key;

- (BOOL)insertWithKey:(NSString *)key :(NSData *)data;

- (NSData *)dataWithKey:(NSString *)key;
@end

@implementation KeyChain {
    NSString *service;
    NSString *group;
}

+ (NSString *)bundleSeedID {
    NSDictionary *query = @{
            (__bridge NSString *) kSecClass: (__bridge NSString *) kSecClassGenericPassword,
            (__bridge NSString *) kSecAttrAccount: @"bundleSeedID",
            (__bridge NSString *) kSecAttrService: @"",
            (__bridge NSString *) kSecReturnAttributes: (id) kCFBooleanTrue
    };
    CFDictionaryRef result = nil;
    OSStatus status = SecItemCopyMatching((__bridge CFDictionaryRef) query, (CFTypeRef *) &result);
    if (status == errSecItemNotFound)
        status = SecItemAdd((__bridge CFDictionaryRef) query, (CFTypeRef *) &result);
    if (status != errSecSuccess)
        return nil;
    NSString *accessGroup = ((__bridge NSDictionary *) result)[(__bridge NSString *) kSecAttrAccessGroup];
    NSArray *components = [accessGroup componentsSeparatedByString:@"."];
    NSString *bundleSeedID = [[components objectEnumerator] nextObject];
    CFRelease(result);
    return bundleSeedID;
}

/**
 * Return a group identifier appended with Application Identifier Prefix.
 * @param key Identifier except for Application Identifier Prefix
 * @return Group Identifier
 */
+ (NSString *)groupIdWithAppIdPrefixWithKey:(NSString *)key {
    NSString *seedId = [KeyChain bundleSeedID];
    NSString *result = [NSString stringWithFormat:@"%@.%@", seedId, key];
    NSLog(@"SeedId : %@, GroupId : %@", seedId, result);
    return result;
}

- (id)initWithService:(NSString *)service_ withGroup:(NSString *)group_ {
    self = [super init];
    if (self) {
        service = [NSString stringWithString:service_];

        if (group_)
            group = [NSString stringWithString:group_];
    }
    return self;
}

- (NSMutableDictionary *)prepareDict:(NSString *)key {
    NSMutableDictionary *dict = [[NSMutableDictionary alloc] init];
    dict[(__bridge id) kSecClass] = (__bridge id) kSecClassGenericPassword;

    NSData *encodedKey = [key dataUsingEncoding:NSUTF8StringEncoding];
    dict[(__bridge id) kSecAttrGeneric] = encodedKey;
    dict[(__bridge id) kSecAttrAccount] = encodedKey;
    dict[(__bridge id) kSecAttrService] = service;
    dict[(__bridge id) kSecAttrAccessible] = (__bridge id) kSecAttrAccessibleAlwaysThisDeviceOnly;

    //This is for sharing data across apps
    if (group != nil)
        dict[(__bridge id) kSecAttrAccessGroup] = group;

    return dict;

}

- (BOOL)insertWithKey:(NSString *)key :(NSData *)data {
    NSMutableDictionary *dict = [self prepareDict:key];
    dict[(__bridge id) kSecValueData] = data;

    OSStatus status = SecItemAdd((__bridge CFDictionaryRef) dict, NULL);
    if (errSecSuccess != status) {
        NSLog(@"Unable add item with key =%@ error:%d", key, (int) status);
    }
    return (errSecSuccess == status);
}

- (BOOL)update:(NSString *)key :(NSData *)data {
    NSMutableDictionary *dictKey = [self prepareDict:key];

    NSMutableDictionary *dictUpdate = [[NSMutableDictionary alloc] init];
    dictUpdate[(__bridge id) kSecValueData] = data;

    OSStatus status = SecItemUpdate((__bridge CFDictionaryRef) dictKey, (__bridge CFDictionaryRef) dictUpdate);
    if (errSecSuccess != status) {
        NSLog(@"Unable add update with key =%@ error:%ld", key, status);
    }
    return (errSecSuccess == status);

    return YES;

}

- (BOOL)remove:(NSString *)key {
    NSMutableDictionary *dict = [self prepareDict:key];
    OSStatus status = SecItemDelete((__bridge CFDictionaryRef) dict);
    if (status != errSecSuccess) {
        NSLog(@"Unable to remove item for key %@ with error:%ld", key, status);
        return NO;
    }
    return YES;
}

- (NSData *)dataWithKey:(NSString *)key {
    NSMutableDictionary *dict = [self prepareDict:key];
    dict[(__bridge id) kSecMatchLimit] = (__bridge id) kSecMatchLimitOne;
    dict[(__bridge id) kSecReturnData] = (id) kCFBooleanTrue;
    CFTypeRef result = NULL;
    OSStatus status = SecItemCopyMatching((__bridge CFDictionaryRef) dict, &result);

    if (status != errSecSuccess) {
        NSLog(@"Unable to fetch item for key %@ with error:%d", key, (int) status);
        return nil;
    }

    return (__bridge NSData *) result;
}
@end

#endif /* KeyChain_h */

ViewController.m

//
//  ViewController.m
//  AppGroupProducer
//
//  Created by VIEWPOINT on 2016. 12. 16..
//  Copyright © 2016년 VIEWPOINT. All rights reserved.
//

#import "ViewController.h"
#import "KeyChain.h"

#define KEYCHAIN
//#define APP_GROUP

@interface ViewController ()
@property(weak, nonatomic) IBOutlet UITextField *textField;
@end

NSString *kDefaultSuiteName = @"group.viewpoint.test";

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.

    [self load];
}

- (void)load {
#ifdef APP_GROUP
    NSUserDefaults* sharedDefault = [[NSUserDefaults alloc] initWithSuiteName:kDefaultSuiteName];
    NSString* text = [sharedDefault objectForKey:@"text"];
    if(text)
        self.textField.text = text;
#else
    KeyChain *chain = [[KeyChain alloc] initWithService:@"Service"
                                              withGroup:[KeyChain groupIdWithAppIdPrefixWithKey:@"com.viewpoint.AppGroupProducer"]];
    NSData *data = [chain dataWithKey:@"text"];
    if (data)
        self.textField.text = [[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding];
#endif
}

- (IBAction)onClickSave:(id)sender {
#ifdef APP_GROUP
    NSString* text = [self.textField text];
    NSUserDefaults* sharedDefault = [[NSUserDefaults alloc] initWithSuiteName:kDefaultSuiteName];
    [sharedDefault setObject:text forKey:@"text"];
    [sharedDefault synchronize];
#else
    KeyChain *chain = [[KeyChain alloc] initWithService:@"Service"
                                              withGroup:[KeyChain groupIdWithAppIdPrefixWithKey:@"com.viewpoint.AppGroupProducer"]];
    if ([chain dataWithKey:@"text"] == nil)
        [chain insertWithKey:@"text" :[[self.textField text] dataUsingEncoding:NSUTF8StringEncoding]];
    else
        [chain update:@"text" :[[self.textField text] dataUsingEncoding:NSUTF8StringEncoding]];
#endif
}

@end