Helper class which adds/gets/deletes entries in the iOS Keychain

MJRKeychainStorage.h

//
//  Class modified from this GitHub repository:
//  https://github.com/jeremangnr/JNKeychain
//

#import <Foundation/Foundation.h>

@interface MJRKeychainStorage : NSObject

/**
 @abstract Saves the given key-value pair to the Keychain.
 @param value The value to save.
 @param key The key identifying the value to save.
 @return YES iff the key-value pair was saved successfully.
 */
- (BOOL)saveValue:(id)value forKey:(NSString *)key;

/**
 @abstract Loads the value from the Keychain which matches the given key.
 @param key The key identifying the value to load.
 @return The value identified by key, or nil in case of error.
 */
- (id)getValueForKey:(NSString *)key;

/**
 @abstract Deletes the given key from the Keychain.
 @param key The key identifying the key-value pair to delete.
 @return YES iff either there is no such key in the Keychain or deletion was successful.
 */
- (BOOL)deleteKey:(NSString *)key;

@end

MJRKeychainStorage.m

//
//  Class modified from this GitHub repository:
//  https://github.com/jeremangnr/JNKeychain
//

#import "MJRKeychainStorage.h"

@implementation MJRKeychainStorage

- (BOOL)saveValue:(id)value forKey:(NSString *)key {
    [self deleteKey:key];

    NSMutableDictionary *query = [self getQueryForKey:key];
    query[(__bridge id) kSecValueData] = [NSKeyedArchiver archivedDataWithRootObject:value];

    OSStatus status = SecItemAdd((__bridge CFDictionaryRef) query, NULL);

    return status == errSecSuccess;
}

- (id)getValueForKey:(NSString *)key {
    NSMutableDictionary *query = [self getQueryForKey:key];
    query[(__bridge id) kSecReturnData] = (__bridge id) kCFBooleanTrue;
    query[(__bridge id) kSecMatchLimit] = (__bridge id) kSecMatchLimitOne;

    CFDataRef keyData = NULL;
    id value = nil;

    if (SecItemCopyMatching((__bridge CFDictionaryRef) query, (CFTypeRef *) &keyData) == noErr) {
        @try {
            value = [NSKeyedUnarchiver unarchiveObjectWithData:(__bridge NSData *) keyData];
        }
        @catch (NSException *e) {
            value = nil;
        }
        @finally {
            //nothing to do
        }
    }

    if (keyData) {
        CFRelease(keyData);
    }

    return value;
}

- (BOOL)deleteKey:(NSString *)key {
    NSMutableDictionary *query = [self getQueryForKey:key];

    OSStatus status = SecItemDelete((__bridge CFDictionaryRef) query);

    return (status == errSecSuccess) || (status == errSecItemNotFound);
}

#pragma mark - Private methods

- (NSMutableDictionary *)getQueryForKey:(NSString *)key {
    NSMutableDictionary *query = [NSMutableDictionary dictionary];

    query[(__bridge id) kSecClass] = (__bridge id) kSecClassGenericPassword;
    query[(__bridge id) kSecAttrService] = key;
    query[(__bridge id) kSecAttrAccount] = key;
    query[(__bridge id) kSecAttrAccessible] = (__bridge id) kSecAttrAccessibleAfterFirstUnlockThisDeviceOnly;

    return query;
}

@end