ios objective-c keychain nsexception keychainitemwrapper

NSInternalInconsistencyException: Couldn't update the Keychain Item

After adding the line to set kSecAttrAccessible to kSecAttrAccessibleAlways to make the keychain accessible even when the screen is locked I started seeing this error. Normally it comes when keychain sharing is not configured, but my keychain sharing is already set up with group ID that contains app’s reference ID:

*** Assertion failure in -[KeychainItemWrapper writeToKeychain], /path/to/project/KeychainItemWrapper.m:278
*** Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: 'Couldn't add the Keychain Item.'
*** First throw call stack:
(0x189eebef8 0x1890b9a40 0x189e0006c 0x18a8ec3e0 0x1026429d4 0x102641d04 0x102688080 0x102687ecc 0x1026bf2f4 0x1026bf4ac 0x1b6d1e2dc 0x1b67af844 0x1b67afb64 0x1b67aeb64 0x1b6d57c14 0x1b6d58e78 0x1b6d383c0 0x1b6e0323c 0x1b6e05ca8 0x1b6dfe83c 0x189e7a5b8 0x189e7a538 0x189e79e1c 0x189e74ce8 0x189e745b8 0x18c0e8584 0x1b6d1cbc8 0x1026627a8 0x189934b94)
libc++abi.dylib: terminating with uncaught exception of type NSException
(lldb)

Stack trace:

Method to store password in my code:

+ (void)storePassword:(NSString *) password {
    KeychainItemWrapper *keychain = [[KeychainItemWrapper alloc] 
                                        initWithIdentifier:@"password" 
                                               accessGroup:@"A123456789.my.access.group"];
    [keychain setObject:password forKey:(__bridge id) kSecValueData];

    if (password.length > 0) {
        [self setUserIsLoggedIn:YES];
    } else {
        [self setUserIsLoggedIn:NO];
    }
}

The added line to KeychainItemWrapper.m:

// CUSTOM QUERY CONSTANTS
[genericPasswordQuery setObject:(__bridge id)kSecAttrAccessibleAlways forKey:(__bridge id)kSecAttrAccessible];

I am using a KeychainItemWrapper 1.2 (by Apple with 1 added line):

/*
 File: KeychainItemWrapper.m
 Abstract:
 Objective-C wrapper for accessing a single keychain item.

 Version: 1.2 - Customized

 Disclaimer: IMPORTANT:  This Apple software is supplied to you by Apple
 Inc. ("Apple") in consideration of your agreement to the following
 terms, and your use, installation, modification or redistribution of
 this Apple software constitutes acceptance of these terms.  If you do
 not agree with these terms, please do not use, install, modify or
 redistribute this Apple software.

 In consideration of your agreement to abide by the following terms, and
 subject to these terms, Apple grants you a personal, non-exclusive
 license, under Apple's copyrights in this original Apple software (the
 "Apple Software"), to use, reproduce, modify and redistribute the Apple
 Software, with or without modifications, in source and/or binary forms;
 provided that if you redistribute the Apple Software in its entirety and
 without modifications, you must retain this notice and the following
 text and disclaimers in all such redistributions of the Apple Software.
 Neither the name, trademarks, service marks or logos of Apple Inc. may
 be used to endorse or promote products derived from the Apple Software
 without specific prior written permission from Apple.  Except as
 expressly stated in this notice, no other rights or licenses, express or
 implied, are granted by Apple herein, including but not limited to any
 patent rights that may be infringed by your derivative works or by other
 works in which the Apple Software may be incorporated.

 The Apple Software is provided by Apple on an "AS IS" basis.  APPLE
 MAKES NO WARRANTIES, EXPRESS OR IMPLIED, INCLUDING WITHOUT LIMITATION
 THE IMPLIED WARRANTIES OF NON-INFRINGEMENT, MERCHANTABILITY AND FITNESS
 FOR A PARTICULAR PURPOSE, REGARDING THE APPLE SOFTWARE OR ITS USE AND
 OPERATION ALONE OR IN COMBINATION WITH YOUR PRODUCTS.

 IN NO EVENT SHALL APPLE BE LIABLE FOR ANY SPECIAL, INDIRECT, INCIDENTAL
 OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 INTERRUPTION) ARISING IN ANY WAY OUT OF THE USE, REPRODUCTION,
 MODIFICATION AND/OR DISTRIBUTION OF THE APPLE SOFTWARE, HOWEVER CAUSED
 AND WHETHER UNDER THEORY OF CONTRACT, TORT (INCLUDING NEGLIGENCE),
 STRICT LIABILITY OR OTHERWISE, EVEN IF APPLE HAS BEEN ADVISED OF THE
 POSSIBILITY OF SUCH DAMAGE.

 Copyright (C) 2010 Apple Inc. All Rights Reserved.

 */

#import "KeychainItemWrapper.h"

/*

 These are the default constants and their respective types,
 available for the kSecClassGenericPassword Keychain Item class:

 kSecAttrAccessGroup            -       CFStringRef
 kSecAttrCreationDate       -       CFDateRef
 kSecAttrModificationDate    -      CFDateRef
 kSecAttrDescription            -       CFStringRef
 kSecAttrComment                -       CFStringRef
 kSecAttrCreator                -       CFNumberRef
 kSecAttrType                -      CFNumberRef
 kSecAttrLabel              -       CFStringRef
 kSecAttrIsInvisible            -       CFBooleanRef
 kSecAttrIsNegative         -       CFBooleanRef
 kSecAttrAccount                -       CFStringRef
 kSecAttrService                -       CFStringRef
 kSecAttrGeneric                -       CFDataRef

 See the header file Security/SecItem.h for more details.

 */

@interface KeychainItemWrapper (PrivateMethods)
/*
 The decision behind the following two methods (secItemFormatToDictionary and dictionaryToSecItemFormat) was
 to encapsulate the transition between what the detail view controller was expecting (NSString *) and what the
 Keychain API expects as a validly constructed container class.
 */
- (NSMutableDictionary *) secItemFormatToDictionary:(NSDictionary *) dictionaryToConvert;
- (NSMutableDictionary *) dictionaryToSecItemFormat:(NSDictionary *) dictionaryToConvert;

// Updates the item in the keychain, or adds it if it doesn't exist.
- (void) writeToKeychain;

@end

@implementation KeychainItemWrapper

@synthesize keychainItemData, genericPasswordQuery;

- (id) initWithIdentifier: (NSString *) identifier accessGroup:(NSString *) accessGroup;
{
    if (self = [super init]) {
        // Begin Keychain search setup. The genericPasswordQuery leverages the special user
        // defined attribute kSecAttrGeneric to distinguish itself between other generic Keychain
        // items which may be included by the same application.
        genericPasswordQuery = [[NSMutableDictionary alloc] init];

        [genericPasswordQuery setObject:(__bridge id)kSecClassGenericPassword forKey:(__bridge id)kSecClass];
        [genericPasswordQuery setObject:identifier forKey:(__bridge id)kSecAttrGeneric];

        // The keychain access group attribute determines if this item can be shared
        // amongst multiple apps whose code signing entitlements contain the same keychain access group.
        if (accessGroup != nil) {
#if TARGET_IPHONE_SIMULATOR
            // Ignore the access group if running on the iPhone simulator.
            //
            // Apps that are built for the simulator aren't signed, so there's no keychain access group
            // for the simulator to check. This means that all apps can see all keychain items when run
            // on the simulator.
            //
            // If a SecItem contains an access group attribute, SecItemAdd and SecItemUpdate on the
            // simulator will return -25243 (errSecNoAccessForItem).
#else
            [genericPasswordQuery setObject:accessGroup forKey:(__bridge id)kSecAttrAccessGroup];
#endif
        }

        // Use the proper search constants, return only the attributes of the first match.
        [genericPasswordQuery setObject:(__bridge id)kSecMatchLimitOne forKey:(__bridge id)kSecMatchLimit];
        [genericPasswordQuery setObject:(__bridge id)kCFBooleanTrue forKey:(__bridge id)kSecReturnAttributes];

        // THIS LINE WAS ADDED TO THE QUERY TO MAKE THE KEYCHAIN ACCESSIBLE WHEN THE SCREEN IS LOCKED
        [genericPasswordQuery setObject:(__bridge id)kSecAttrAccessibleAlways forKey:(__bridge id)kSecAttrAccessible];

        NSDictionary *tempQuery = [NSDictionary dictionaryWithDictionary:genericPasswordQuery];

        NSMutableDictionary *outDictionary = nil;

        if (!SecItemCopyMatching((__bridge CFDictionaryRef)tempQuery, (void *)&outDictionary) == noErr) {
            // Stick these default values into keychain item if nothing found.
            [self resetKeychainItem];

            // Add the generic attribute and the keychain access group.
            [keychainItemData setObject:identifier forKey:(__bridge id)kSecAttrGeneric];
            if (accessGroup != nil) {
#if TARGET_IPHONE_SIMULATOR
                // Ignore the access group if running on the iPhone simulator.
                //
                // Apps that are built for the simulator aren't signed, so there's no keychain access group
                // for the simulator to check. This means that all apps can see all keychain items when run
                // on the simulator.
                //
                // If a SecItem contains an access group attribute, SecItemAdd and SecItemUpdate on the
                // simulator will return -25243 (errSecNoAccessForItem).
#else
                [keychainItemData setObject:accessGroup forKey:(__bridge id)kSecAttrAccessGroup];
#endif
            }
        } else           {
            // load the saved data from Keychain.
            self.keychainItemData = [self secItemFormatToDictionary:outDictionary];
        }

    }

    return self;
}

- (void) setObject:(id) inObject forKey:(id) key {
    if (inObject == nil) return;
    id currentObject = [keychainItemData objectForKey:key];
    if (![currentObject isEqual:inObject]) {
        [keychainItemData setObject:inObject forKey:key];
        [self writeToKeychain];
    }
}

- (id) objectForKey:(id) key {
    return [keychainItemData objectForKey:key];
}

- (void) resetKeychainItem {
    OSStatus junk = noErr;
    if (!keychainItemData) {
        self.keychainItemData = [[NSMutableDictionary alloc] init];
    } else if (keychainItemData)   {
        NSMutableDictionary *tempDictionary = [self dictionaryToSecItemFormat:keychainItemData];
        junk = SecItemDelete((__bridge CFDictionaryRef)tempDictionary);
        NSAssert(junk == noErr || junk == errSecItemNotFound, @"Problem deleting current dictionary.");
    }

    // Default attributes for keychain item.
    [keychainItemData setObject:@"" forKey:(__bridge id)kSecAttrAccount];
    [keychainItemData setObject:@"" forKey:(__bridge id)kSecAttrLabel];
    [keychainItemData setObject:@"" forKey:(__bridge id)kSecAttrDescription];

    // Default data for keychain item.
    [keychainItemData setObject:@"" forKey:(__bridge id)kSecValueData];
}

- (NSMutableDictionary *) dictionaryToSecItemFormat:(NSDictionary *) dictionaryToConvert {
    // The assumption is that this method will be called with a properly populated dictionary
    // containing all the right key/value pairs for a SecItem.

    // Create a dictionary to return populated with the attributes and data.
    NSMutableDictionary *returnDictionary = [NSMutableDictionary dictionaryWithDictionary:dictionaryToConvert];

    // Add the Generic Password keychain item class attribute.
    [returnDictionary setObject:(__bridge id)kSecClassGenericPassword forKey:(__bridge id)kSecClass];

    // Convert the NSString to NSData to meet the requirements for the value type kSecValueData.
    // This is where to store sensitive data that should be encrypted.
    NSString *passwordString = [dictionaryToConvert objectForKey:(__bridge id)kSecValueData];
    [returnDictionary setObject:[passwordString dataUsingEncoding:NSUTF8StringEncoding] forKey:(__bridge id)kSecValueData];

    return returnDictionary;
}

- (NSMutableDictionary *) secItemFormatToDictionary:(NSDictionary *) dictionaryToConvert {
    // The assumption is that this method will be called with a properly populated dictionary
    // containing all the right key/value pairs for the UI element.

    // Create a dictionary to return populated with the attributes and data.
    NSMutableDictionary *returnDictionary = [NSMutableDictionary dictionaryWithDictionary:dictionaryToConvert];

    // Add the proper search key and class attribute.
    [returnDictionary setObject:(__bridge id)kCFBooleanTrue forKey:(__bridge id)kSecReturnData];
    [returnDictionary setObject:(__bridge id)kSecClassGenericPassword forKey:(__bridge id)kSecClass];

    // Acquire the password data from the attributes.
    NSData *passwordData = NULL;
    if (SecItemCopyMatching((__bridge CFDictionaryRef)returnDictionary, (void *)&passwordData) == noErr) {
        // Remove the search, class, and identifier key/value, we don't need them anymore.
        [returnDictionary removeObjectForKey:(__bridge id)kSecReturnData];

        // Add the password to the dictionary, converting from NSData to NSString.
        NSString *password = [[NSString alloc] initWithBytes:[passwordData bytes] length:[passwordData length]
                                                     encoding:NSUTF8StringEncoding];
        [returnDictionary setObject:password forKey:(__bridge id)kSecValueData];
    } else   {
        // Don't do anything if nothing is found.
        NSAssert(NO, @"Serious error, no matching item found in the keychain.\n");
    }

    return returnDictionary;
}

- (void) writeToKeychain {
    NSDictionary *attributes = NULL;
    NSMutableDictionary *updateItem = NULL;
    OSStatus result;

    if (SecItemCopyMatching((__bridge CFDictionaryRef)genericPasswordQuery, (void *)&attributes) == noErr) {
        // First we need the attributes from the Keychain.
        updateItem = [NSMutableDictionary dictionaryWithDictionary:attributes];
        // Second we need to add the appropriate search key/values.
        [updateItem setObject:[genericPasswordQuery objectForKey:(__bridge id)kSecClass] forKey:(__bridge id)kSecClass];

        // Lastly, we need to set up the updated attribute list being careful to remove the class.
        NSMutableDictionary *tempCheck = [self dictionaryToSecItemFormat:keychainItemData];
        [tempCheck removeObjectForKey:(__bridge id)kSecClass];

#if TARGET_IPHONE_SIMULATOR
        // Remove the access group if running on the iPhone simulator.
        //
        // Apps that are built for the simulator aren't signed, so there's no keychain access group
        // for the simulator to check. This means that all apps can see all keychain items when run
        // on the simulator.
        //
        // If a SecItem contains an access group attribute, SecItemAdd and SecItemUpdate on the
        // simulator will return -25243 (errSecNoAccessForItem).
        //
        // The access group attribute will be included in items returned by SecItemCopyMatching,
        // which is why we need to remove it before updating the item.
        [tempCheck removeObjectForKey:(__bridge id)kSecAttrAccessGroup];
#endif

        // An implicit assumption is that you can only update a single item at a time.

        result = SecItemUpdate((__bridge CFDictionaryRef)updateItem, (__bridge CFDictionaryRef)tempCheck);
        NSAssert(result == noErr, @"Couldn't update the Keychain Item.");
    } else   {
        // No previous item found; add the new one.
        result = SecItemAdd((__bridge CFDictionaryRef)[self dictionaryToSecItemFormat: keychainItemData], NULL);
        NSAssert(result == noErr, @"Couldn't add the Keychain Item.");
    }
}

@end

Solution

The solution was to setup logging of the keychain result, so I created a new method that - (void) createLogEntry:(OSStatus) result; that transcribes the result code of the SecItemAdd function into a readable message.

The full list of the Security Framework Result Codes it returns is here: https://developer.apple.com/documentation/security/1542001-security_framework_result_codes?language=objc

- (void) writeToKeychain {
    NSDictionary *attributes = NULL;
    NSMutableDictionary *updateItem = NULL;
    OSStatus result;

    if (SecItemCopyMatching((__bridge CFDictionaryRef)genericPasswordQuery, (void *)&attributes) == noErr) {
        // First we need the attributes from the Keychain.
        updateItem = [NSMutableDictionary dictionaryWithDictionary:attributes];
        // Second we need to add the appropriate search key/values.
        [updateItem setObject:[genericPasswordQuery objectForKey:(__bridge id)kSecClass] forKey:(__bridge id)kSecClass];

        // Lastly, we need to set up the updated attribute list being careful to remove the class.
        NSMutableDictionary *tempCheck = [self dictionaryToSecItemFormat:keychainItemData];
        [tempCheck removeObjectForKey:(__bridge id)kSecClass];

#if TARGET_IPHONE_SIMULATOR
        // Remove the access group if running on the iPhone simulator.
        //
        // Apps that are built for the simulator aren't signed, so there's no keychain access group
        // for the simulator to check. This means that all apps can see all keychain items when run
        // on the simulator.
        //
        // If a SecItem contains an access group attribute, SecItemAdd and SecItemUpdate on the
        // simulator will return -25243 (errSecNoAccessForItem).
        //
        // The access group attribute will be included in items returned by SecItemCopyMatching,
        // which is why we need to remove it before updating the item.
        [tempCheck removeObjectForKey:(__bridge id)kSecAttrAccessGroup];
#endif

        // An implicit assumption is that you can only update a single item at a time.

        result = SecItemUpdate((__bridge CFDictionaryRef)updateItem, (__bridge CFDictionaryRef)tempCheck);

        [self createLogEntry:result];

        NSAssert(result == noErr, @"Couldn't update the Keychain Item.");
    } else   {
        // No previous item found; add the new one.
        result = SecItemAdd((__bridge CFDictionaryRef)[self dictionaryToSecItemFormat: keychainItemData], NULL);

        [self createLogEntry:result];

        NSAssert(result == noErr, @"Couldn't add the Keychain Item.");
    }
}

- (void) createLogEntry:(OSStatus) result {
    if (@available(iOS 11.3, *)) {
        NSString *message = CFBridgingRelease(SecCopyErrorMessageString(result, nil));
        DDLogDebug(@"writeToKeychain result={%d} message={%@}",(int)result, message);
    } else {
        // Fallback on earlier versions
    }
}

With the logging set up I found out that the problem was that I was reinstantiating the KeychainItemWrapper each time I needed the password to be stored/retrieved by calling:

[[KeychainItemWrapper alloc] initWithIdentifier:@"password" accessGroup:@"A123456789my.access.group"];

This caused inconsistencies between the wrapper and the keychain because it was trying to save an item that already existed. Specifically the error code errSecDuplicateItem = -25299 "The item already exists" was returned.