Store NSDictionary in keychain

Question

It is possible to store a NSDictionary in the iPhone keychain, using KeychainItemWrapper (or without)? If it's not possible, have you another solution?

Answer 1

Encoding : [dic description]
Decoding : [dic propertyList]

Answer 2

I found that the keychain wrapper only wants strings. Not even NSData. So to store a dictionary you'll have to do as Bret suggested, but with an extra step to convert the NSData serialization to a string. Like this:

NSString *error;
KeychainItemWrapper *keychain = [[KeychainItemWrapper alloc] initWithIdentifier:MY_STRING accessGroup:nil];
NSData *dictionaryRep = [NSPropertyListSerialization dataFromPropertyList:dictToSave format:NSPropertyListXMLFormat_v1_0 errorDescription:&error];
NSString *xml = [[NSString alloc] initWithBytes:[dictionaryRep bytes] length:[dictionaryRep length] encoding:NSUTF8StringEncoding];
[keychain setObject:xml forKey:(__bridge id)(kSecValueData)];

Reading it back:

NSError *error;
NSString *xml = [keychain objectForKey:(__bridge id)(kSecValueData)];
if (xml && xml.length) {
    NSData *dictionaryRep = [xml dataUsingEncoding:NSUTF8StringEncoding];
    dict = [NSPropertyListSerialization propertyListWithData:dictionaryRep options:NSPropertyListImmutable format:nil error:&error];
    if (error) {
        NSLog(@"%@", error);
    }
}

Answer 3

Using the KeychainItemWrapper dependency requires modifying the library/sample code to accept NSData as the encrypted payload, which is not future proof. Also, doing the NSDictionary > NSData > NSString conversion sequence just so that you can use KeychainItemWrapper is inefficient: KeychainItemWrapper will convert your string back to NSData anyway, to encrypt it.

Here's a complete solution that solves the above by utilizing the keychain library directly. It is implemented as a category so you use it like this:

// to store your dictionary
[myDict storeToKeychainWithKey:@"myStorageKey"];

// to retrieve it
NSDictionary *myDict = [NSDictionary dictionaryFromKeychainWithKey:@"myStorageKey"];

// to delete it
[myDict deleteFromKeychainWithKey:@"myStorageKey"];

and here's the Category:

@implementation NSDictionary (Keychain)

-(void) storeToKeychainWithKey:(NSString *)aKey {
    // serialize dict
    NSString *error;
    NSData *serializedDictionary = [NSPropertyListSerialization dataFromPropertyList:self format:NSPropertyListXMLFormat_v1_0 errorDescription:&error];

    // encrypt in keychain
    if(!error) {
        // first, delete potential existing entries with this key (it won't auto update)
        [self deleteFromKeychainWithKey:aKey];

        // setup keychain storage properties
        NSDictionary *storageQuery = @{
            (id)kSecAttrAccount:    aKey,
            (id)kSecValueData:      serializedDictionary,
            (id)kSecClass:          (id)kSecClassGenericPassword,
            (id)kSecAttrAccessible: (id)kSecAttrAccessibleWhenUnlocked
        };
        OSStatus osStatus = SecItemAdd((CFDictionaryRef)storageQuery, nil);
        if(osStatus != noErr) {
            // do someting with error
        }
    }
}


+(NSDictionary *) dictionaryFromKeychainWithKey:(NSString *)aKey {
    // setup keychain query properties
    NSDictionary *readQuery = @{
        (id)kSecAttrAccount: aKey,
        (id)kSecReturnData: (id)kCFBooleanTrue,
        (id)kSecClass:      (id)kSecClassGenericPassword
    };

    NSData *serializedDictionary = nil;
    OSStatus osStatus = SecItemCopyMatching((CFDictionaryRef)readQuery, (CFTypeRef *)&serializedDictionary);
    if(osStatus == noErr) {
        // deserialize dictionary
        NSString *error;
        NSDictionary *storedDictionary = [NSPropertyListSerialization propertyListFromData:serializedDictionary mutabilityOption:NSPropertyListImmutable format:nil errorDescription:&error];
        if(error) {
            NSLog(@"%@", error);
        }
        return storedDictionary;
    }
    else {
        // do something with error
        return nil;
    }
}


-(void) deleteFromKeychainWithKey:(NSString *)aKey {
    // setup keychain query properties
    NSDictionary *deletableItemsQuery = @{
        (id)kSecAttrAccount:        aKey,
        (id)kSecClass:              (id)kSecClassGenericPassword,
        (id)kSecMatchLimit:         (id)kSecMatchLimitAll,
        (id)kSecReturnAttributes:   (id)kCFBooleanTrue
    };

    NSArray *itemList = nil;
    OSStatus osStatus = SecItemCopyMatching((CFDictionaryRef)deletableItemsQuery, (CFTypeRef *)&itemList);
    // each item in the array is a dictionary
    for (NSDictionary *item in itemList) {
        NSMutableDictionary *deleteQuery = [item mutableCopy];
        [deleteQuery setValue:(id)kSecClassGenericPassword forKey:(id)kSecClass];
        // do delete
        osStatus = SecItemDelete((CFDictionaryRef)deleteQuery);
        if(osStatus != noErr) {
            // do something with error
        }
        [deleteQuery release];
    }
}


@end

In fact, you can modify it easily to store any kind of serializable object in the keychain, not just a dictionary. Just make an NSData representation of the object you want to store.

Answer 4

Made few minor changes to Dts category. Converted to ARC and using NSKeyedArchiver to store custom objects.

@implementation NSDictionary (Keychain)

-(void) storeToKeychainWithKey:(NSString *)aKey {
    // serialize dict
    NSData *serializedDictionary = [NSKeyedArchiver archivedDataWithRootObject:self];
    // encrypt in keychain
        // first, delete potential existing entries with this key (it won't auto update)
        [self deleteFromKeychainWithKey:aKey];

        // setup keychain storage properties
        NSDictionary *storageQuery = @{
                                       (__bridge id)kSecAttrAccount:    aKey,
                                       (__bridge id)kSecValueData:      serializedDictionary,
                                       (__bridge id)kSecClass:          (__bridge id)kSecClassGenericPassword,
                                       (__bridge id)kSecAttrAccessible: (__bridge id)kSecAttrAccessibleWhenUnlocked
                                       };
        OSStatus osStatus = SecItemAdd((__bridge CFDictionaryRef)storageQuery, nil);
        if(osStatus != noErr) {
            // do someting with error
        }
}


+(NSDictionary *) dictionaryFromKeychainWithKey:(NSString *)aKey {
    // setup keychain query properties
    NSDictionary *readQuery = @{
                                (__bridge id)kSecAttrAccount: aKey,
                                (__bridge id)kSecReturnData: (id)kCFBooleanTrue,
                                (__bridge id)kSecClass:      (__bridge id)kSecClassGenericPassword
                                };

    CFDataRef serializedDictionary = NULL;
    OSStatus osStatus = SecItemCopyMatching((__bridge CFDictionaryRef)readQuery, (CFTypeRef *)&serializedDictionary);
    if(osStatus == noErr) {
        // deserialize dictionary
        NSData *data = (__bridge NSData *)serializedDictionary;
        NSDictionary *storedDictionary = [NSKeyedUnarchiver unarchiveObjectWithData:data];
        return storedDictionary;
    }
    else {
        // do something with error
        return nil;
    }
}


-(void) deleteFromKeychainWithKey:(NSString *)aKey {
    // setup keychain query properties
    NSDictionary *deletableItemsQuery = @{
                                          (__bridge id)kSecAttrAccount:        aKey,
                                          (__bridge id)kSecClass:              (__bridge id)kSecClassGenericPassword,
                                          (__bridge id)kSecMatchLimit:         (__bridge id)kSecMatchLimitAll,
                                          (__bridge id)kSecReturnAttributes:   (id)kCFBooleanTrue
                                          };

    CFArrayRef itemList = nil;
    OSStatus osStatus = SecItemCopyMatching((__bridge CFDictionaryRef)deletableItemsQuery, (CFTypeRef *)&itemList);
    // each item in the array is a dictionary
    NSArray *itemListArray = (__bridge NSArray *)itemList;
    for (NSDictionary *item in itemListArray) {
        NSMutableDictionary *deleteQuery = [item mutableCopy];
        [deleteQuery setValue:(__bridge id)kSecClassGenericPassword forKey:(__bridge id)kSecClass];
        // do delete
        osStatus = SecItemDelete((__bridge CFDictionaryRef)deleteQuery);
        if(osStatus != noErr) {
            // do something with error
        }
    }
}

@end

Answer 5

You must properly serialize the NSDictionary before storing it into the Keychain. Using:

[dic description]
[dic propertyList]

you will end up with a NSDictionary collection of only NSString objects. If you want to maintain the data types of the objects, you can use NSPropertyListSerialization.

KeychainItemWrapper *keychain = [[KeychainItemWrapper alloc] initWithIdentifier:@"arbitraryId" accessGroup:nil]
NSString *error;
//The following NSData object may be stored in the Keychain
NSData *dictionaryRep = [NSPropertyListSerialization dataFromPropertyList:dictionary format:NSPropertyListXMLFormat_v1_0 errorDescription:&error];
[keychain setObject:dictionaryRep forKey:kSecValueData];

//When the NSData object object is retrieved from the Keychain, you convert it back to NSDictionary type
dictionaryRep = [keychain objectForKey:kSecValueData];
NSDictionary *dictionary = [NSPropertyListSerialization propertyListFromData:dictionaryRep mutabilityOption:NSPropertyListImmutable format:nil errorDescription:&error];

if (error) {
    NSLog(@"%@", error);
}

The NSDictionary returned by the second call to NSPropertyListSerialization will maintain original data types within the NSDictionary collection.

Answer 6

You can store anything, you just need to serialize it.

NSData *data = [NSKeyedArchiver archivedDataWithRootObject:dictionary];

You should be able to store that data in the keychain.