manager for KeychainAccess. suitable for ARC.

KeychainAccessGroups.plist

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
	<key>application-identifier</key>
	<string>$(AppIdentifierPrefix)$(CFBundleIdentifier)</string>
	<key>keychain-access-groups</key>
	<array>
		<string>$(AppIdentifierPrefix)yourAccessGroup</string>
	</array>
</dict>
</plist>

ZTMKeychainManager.m

//
//  ZTMKeychainManager.m
//
//  Created by Kechol on 2012/11/24.
//  Copyright (c) 2012 Kechol.
//

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


@interface ZTMKeychainManager()

@end

@implementation ZTMKeychainManager

static NSString * const kAccessGroup = @"APPPREFIX.yourAccessGroup";
static NSString * const kService     = @"set.your.app.identifier";

- (id)initWithIdentifier: (NSString *)identifier
{
    if (self = [super init])
    {
        _defaultDict = [NSMutableDictionary dictionary];
        
		[_defaultDict setObject:(__bridge id)kSecClassGenericPassword forKey:(__bridge id)kSecClass];
        [_defaultDict setObject:(id)kCFBooleanTrue forKey:(__bridge id)kSecReturnAttributes];
        
        #if !TARGET_IPHONE_SIMULATOR
        [_defaultDict setObject:kAccessGroup forKey:(__bridge id)kSecAttrAccessGroup];
        [_defaultDict setObject:kService forKey:(__bridge id)kSecAttrService];
        #endif
		
        NSDictionary *query = [NSDictionary dictionaryWithDictionary:_defaultDict];
        CFMutableDictionaryRef dict = NULL;
        
        if (SecItemCopyMatching((__bridge CFDictionaryRef)query, (CFTypeRef *)&dict) == noErr) {
            account  = [(__bridge NSMutableDictionary *)dict objectForKey:(__bridge id)kSecAttrAccount];
            password = [(__bridge NSMutableDictionary *)dict objectForKey:(__bridge id)kSecValueData];
        }
        
        if(dict) CFRelease(dict);
    }
    
    [self dumpItems];
    
	return self;
}

- (void)setAccount:(NSString *)acct AndPassword:(NSString *)pswd
{
    account  = acct;
    password = [pswd dataUsingEncoding:NSUTF8StringEncoding];
    
    NSMutableDictionary *query = [NSMutableDictionary dictionaryWithDictionary:self.defaultDict];
    CFMutableDictionaryRef dict = NULL;
    
    NSMutableDictionary *attributes = [NSMutableDictionary dictionary];
    [attributes setObject:(__bridge id)kSecClassGenericPassword forKey:(__bridge id)kSecClass];
    [attributes setObject:account  forKey:(__bridge id)kSecAttrAccount];
    [attributes setObject:password forKey:(__bridge id)kSecValueData];
    
    NSLog(@"SecSearchDict: %@", query);
    
    OSStatus err = SecItemCopyMatching((__bridge CFDictionaryRef)query, (CFTypeRef *)&dict);
    if (err == noErr) {
        err = SecItemUpdate((__bridge CFDictionaryRef)query, (__bridge CFDictionaryRef)attributes);
        if (err != noErr) {
            NSLog(@"SecItemUpdateError: %ld", err);
        } else {
            NSLog(@"SecItemUpdateSuccess: %@", attributes);
        }
    } else if(err == errSecItemNotFound) {
        [attributes setObject:kService forKey:(__bridge id)kSecAttrService];
        err = SecItemAdd((__bridge CFDictionaryRef)attributes, NULL);
        if (err != noErr) {
            NSLog(@"SecItemAddError: %ld", err);
        } else {
            NSLog(@"SecItemAddSuccess: %@", attributes);
        }
    }
    
    if(dict) CFRelease(dict);
}

- (NSString *)account
{
    NSMutableDictionary *query = [NSMutableDictionary dictionaryWithDictionary:self.defaultDict];
    [query setObject:(id)kCFBooleanTrue forKey:(__bridge id)kSecReturnAttributes];
    CFMutableDictionaryRef dict = NULL;
    
    OSStatus err = SecItemCopyMatching((__bridge CFDictionaryRef)query, (CFTypeRef *)&dict);
    if(err == noErr) {
        return [(__bridge NSMutableDictionary *)dict objectForKey:(__bridge id)kSecAttrAccount];
    } else {
        NSLog(@"SecAccountError: %ld", err);
        if(account) return account;
    }
    if(dict) CFRelease(dict);
    
    return nil;
}

- (NSString *)password
{
    NSMutableDictionary *query = [NSMutableDictionary dictionaryWithDictionary:self.defaultDict];
    [query setObject:(id)kCFBooleanTrue forKey:(__bridge id)kSecReturnData];
    CFMutableDictionaryRef dict = NULL;
    
    NSLog(@"SecSearchDict: %@", query);
    
    OSStatus err = SecItemCopyMatching((__bridge CFDictionaryRef)query, (CFTypeRef *)&dict);
    if(err == noErr) {
        NSData *pswd = [(__bridge NSMutableDictionary *)dict objectForKey:(__bridge id)kSecValueData];
        return [[NSString alloc] initWithData:pswd encoding:NSUTF8StringEncoding];
    } else {
        NSLog(@"SecPasswordError: %ld", err);
        if(password) return [[NSString alloc] initWithData:password encoding:NSUTF8StringEncoding];
    }
    if(dict) CFRelease(dict);
    
    return nil;
}

- (void)deleteItem
{
	OSStatus err = noErr;
    if (account || password) {
        NSMutableDictionary *attributes = [NSMutableDictionary dictionary];
        [attributes setObject:(__bridge id)kSecClassGenericPassword forKey:(__bridge id)kSecClass];
        [attributes setObject:kService forKey:(__bridge id)kSecAttrService];
        [attributes setObject:(id)account  forKey:(__bridge id)kSecAttrAccount];
        
		err = SecItemDelete((__bridge CFDictionaryRef)attributes);
        if(!(err == noErr || err == errSecItemNotFound)) {
            NSLog(@"SecItemDeleteError: %ld", err);
        }
    }
}

- (void)dumpItems
{
    NSMutableDictionary *query = [NSMutableDictionary dictionary];
    
    [query setObject:(__bridge id)kSecClassGenericPassword forKey:(__bridge id)kSecClass];
    [query setObject:(id)kCFBooleanTrue forKey:(__bridge id)kSecReturnAttributes];
    [query setObject:(__bridge id)kSecMatchLimitAll forKey:(__bridge id)kSecMatchLimit];
    
    CFArrayRef result = NULL;
    OSStatus err = SecItemCopyMatching((__bridge CFDictionaryRef)query,(CFTypeRef *)&result);
    
    if (err == noErr) {
        NSLog(@"SecDumpResult: %@", result);
    } else if(err == errSecItemNotFound) {
        NSLog(@"SecDumpNotFound: %ld", err);
    } else {
        NSLog(@"SecDumpError: %ld", err);
    }
    
}



@end

ZTMKeychainManger.h

//
//  ZTMKeychainManager.h
//
//  Created by Kechol on 2012/11/24.
//  Copyright (c) 2012 Kechol.
//

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

@interface ZTMKeychainManager : NSObject {
    NSString *account;
    NSData   *password;
}

@property (nonatomic, retain) NSMutableDictionary *defaultDict;

- (id)initWithIdentifier: (NSString *)identifier;
- (void)setAccount:(NSString *)acct AndPassword:(NSString *)pswd;
- (void)deleteItem;
- (void)dumpItems;
- (NSString *)account;
- (NSString *)password;

@end