ios 5.0 keychain access

Question

I want to store user credentials in the keychain. I found this: http://developer.apple.com/library/ios/#samplecode/GenericKeychain/Listings/Classes_KeychainItemWrapper_m.html#//apple_ref/doc/uid/DTS40007797-Classes_KeychainItemWrapper_m-DontLinkElementID_10

I added the KeychainItemWrapper.h/.m to my project. Unfortunately it doesn't compile. I'm targeting iOS 5, guessing that's the problem.

For example, this line:

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

gives me this error:

cast of C pointer type 'CFTypeRef' (aka 'const void *') to Objective-C pointer type 'id' requires a bridged cast

I tried the "fix its", but it just introduced different errors.

Suggestions on how to proceed? I find it odd this wrapper isn't built into the SDK in the first place. Is there an new API/example for iOS 5? I couldn't find one. And is iOS 5 really still under NDA?

Answer 1

Turning ARC off is a short-sighted answer. I included an ARC-compatible version of the KeychainWrapper below.

I got it from this project.

Note: Experts on the matter (see comments below) think this is a better implementation: https://gist.github.com/1170641

Also, note that KeyChain credentials persist after your app is deleted. If you're using this for token authentication, you may consider NSUserDefaults instead. See this post for more info.

//File: KeychainWrapper.h
#import <UIKit/UIKit.h>

@interface KeychainWrapper : NSObject {}

+ (NSString *) getPasswordForUsername: (NSString *) username andServiceName: (NSString *) serviceName error: (NSError **) error;
+ (BOOL) storeUsername: (NSString *) username andPassword: (NSString *) password forServiceName: (NSString *) serviceName updateExisting: (BOOL) updateExisting error: (NSError **) error;
+ (BOOL) deleteItemForUsername: (NSString *) username andServiceName: (NSString *) serviceName error: (NSError **) error;

@end

and the implementation:

//File: KeychainWrapper.m
#import "KeychainWrapper.h"
#import <Security/Security.h>


static NSString *KeychainWrapperErrorDomain = @"KeychainWrapperErrorDomain";

#if __IPHONE_OS_VERSION_MIN_REQUIRED < 30000 && TARGET_IPHONE_SIMULATOR
@interface KeychainWrapper (PrivateMethods)
+ (SecKeychainItemRef) getKeychainItemReferenceForUsername: (NSString *) username andServiceName: (NSString *) serviceName error: (NSError **) error;
@end
#endif

@implementation KeychainWrapper

#if __IPHONE_OS_VERSION_MIN_REQUIRED < 30000 && TARGET_IPHONE_SIMULATOR

+ (NSString *) getPasswordForUsername: (NSString *) username andServiceName: (NSString *) serviceName error: (NSError **) error {
    if (!username || !serviceName) {
        *error = [NSError errorWithDomain: KeychainWrapperErrorDomain code: -2000 userInfo: nil];
        return nil;
    }

    SecKeychainItemRef item = [KeychainWrapper getKeychainItemReferenceForUsername: username andServiceName: serviceName error: error];

    if (*error || !item) {
        return nil;
    }

    // from Advanced Mac OS X Programming, ch. 16
    UInt32 length;
    char *password;
    SecKeychainAttribute attributes[8];
    SecKeychainAttributeList list;

    attributes[0].tag = kSecAccountItemAttr;
    attributes[1].tag = kSecDescriptionItemAttr;
    attributes[2].tag = kSecLabelItemAttr;
    attributes[3].tag = kSecModDateItemAttr;

    list.count = 4;
    list.attr = attributes;

    OSStatus status = SecKeychainItemCopyContent(item, NULL, &list, &length, (void **)&password);

    if (status != noErr) {
        *error = [NSError errorWithDomain: KeychainWrapperErrorDomain code: status userInfo: nil];
        return nil;
    }

    NSString *passwordString = nil;

    if (password != NULL) {
        char passwordBuffer[1024];

        if (length > 1023) {
            length = 1023;
        }
        strncpy(passwordBuffer, password, length);

        passwordBuffer[length] = '\0';
        passwordString = [NSString stringWithCString:passwordBuffer];
    }

    SecKeychainItemFreeContent(&list, password);

    CFRelease(item);

    return passwordString;
}

+ (void) storeUsername: (NSString *) username andPassword: (NSString *) password forServiceName: (NSString *) serviceName updateExisting: (BOOL) updateExisting error: (NSError **) error { 
    if (!username || !password || !serviceName) {
        *error = [NSError errorWithDomain: KeychainWrapperErrorDomain code: -2000 userInfo: nil];
        return;
    }

    OSStatus status = noErr;

    SecKeychainItemRef item = [KeychainWrapper getKeychainItemReferenceForUsername: username andServiceName: serviceName error: error];

    if (*error && [*error code] != noErr) {
        return;
    }

    *error = nil;

    // null means it's in the default keychain
    if (item) {
        status = SecKeychainItemModifyAttributesAndData(item,
                                                        NULL,
                                                        strlen([password UTF8String]),
                                                        [password UTF8String]);

        CFRelease(item);
    }
    else {
        status = SecKeychainAddGenericPassword(NULL,                                     
                                               strlen([serviceName UTF8String]), 
                                               [serviceName UTF8String],
                                               strlen([username UTF8String]),                        
                                               [username UTF8String],
                                               strlen([password UTF8String]),
                                               [password UTF8String],
                                               NULL);
    }

    if (status != noErr) {
        *error = [NSError errorWithDomain: KeychainWrapperErrorDomain code: status userInfo: nil];
    }
}

+ (void) deleteItemForUsername: (NSString *) username andServiceName: (NSString *) serviceName error: (NSError **) error {
    if (!username || !serviceName) {
        *error = [NSError errorWithDomain: KeychainWrapperErrorDomain code: 2000 userInfo: nil];
        return;
    }

    *error = nil;

    SecKeychainItemRef item = [KeychainWrapper getKeychainItemReferenceForUsername: username andServiceName: serviceName error: error];

    if (*error && [*error code] != noErr) {
        return;
    }

    OSStatus status;

    if (item) {
        status = SecKeychainItemDelete(item);

        CFRelease(item);
    }

    if (status != noErr) {
        *error = [NSError errorWithDomain: KeychainWrapperErrorDomain code: status userInfo: nil];
    }
}

+ (SecKeychainItemRef) getKeychainItemReferenceForUsername: (NSString *) username andServiceName: (NSString *) serviceName error: (NSError **) error {
    if (!username || !serviceName) {
        *error = [NSError errorWithDomain: KeychainWrapperErrorDomain code: -2000 userInfo: nil];
        return nil;
    }

    *error = nil;

    SecKeychainItemRef item;

    OSStatus status = SecKeychainFindGenericPassword(NULL,
                                                     strlen([serviceName UTF8String]),
                                                     [serviceName UTF8String],
                                                     strlen([username UTF8String]),
                                                     [username UTF8String],
                                                     NULL,
                                                     NULL,
                                                     &item);

    if (status != noErr) {
        if (status != errSecItemNotFound) {
            *error = [NSError errorWithDomain: KeychainWrapperErrorDomain code: status userInfo: nil];
        }

        return nil;     
    }

    return item;
}

#else

+ (NSString *) getPasswordForUsername: (NSString *) username andServiceName: (NSString *) serviceName error: (NSError **) error {
    if (!username || !serviceName) {
        if (error != nil) {
            *error = [NSError errorWithDomain: KeychainWrapperErrorDomain code: -2000 userInfo: nil];
        }
        return nil;
    }

    if (error != nil) {
        *error = nil;
    }

    // Set up a query dictionary with the base query attributes: item type (generic), username, and service

    NSArray *keys = [[NSArray alloc] initWithObjects: (__bridge_transfer NSString *) kSecClass, kSecAttrAccount, kSecAttrService, nil];
    NSArray *objects = [[NSArray alloc] initWithObjects: (__bridge_transfer NSString *) kSecClassGenericPassword, username, serviceName, nil];

    NSMutableDictionary *query = [[NSMutableDictionary alloc] initWithObjects: objects forKeys: keys];

    // First do a query for attributes, in case we already have a Keychain item with no password data set.
    // One likely way such an incorrect item could have come about is due to the previous (incorrect)
    // version of this code (which set the password as a generic attribute instead of password data).

    NSMutableDictionary *attributeQuery = [query mutableCopy];
    [attributeQuery setObject: (id) kCFBooleanTrue forKey:(__bridge_transfer id) kSecReturnAttributes];
    CFTypeRef attrResult = NULL;
    OSStatus status = SecItemCopyMatching((__bridge_retained CFDictionaryRef) attributeQuery, &attrResult);
    //NSDictionary *attributeResult = (__bridge_transfer NSDictionary *)attrResult;

    if (status != noErr) {
        // No existing item found--simply return nil for the password
        if (error != nil && status != errSecItemNotFound) {
            //Only return an error if a real exception happened--not simply for "not found."
            *error = [NSError errorWithDomain: KeychainWrapperErrorDomain code: status userInfo: nil];
        }

        return nil;
    }

    // We have an existing item, now query for the password data associated with it.

    NSMutableDictionary *passwordQuery = [query mutableCopy];
    [passwordQuery setObject: (id) kCFBooleanTrue forKey: (__bridge_transfer id) kSecReturnData];
    CFTypeRef resData = NULL;
    status = SecItemCopyMatching((__bridge_retained CFDictionaryRef) passwordQuery, (CFTypeRef *) &resData);
    NSData *resultData = (__bridge_transfer NSData *)resData;

    if (status != noErr) {
        if (status == errSecItemNotFound) {
            // We found attributes for the item previously, but no password now, so return a special error.
            // Users of this API will probably want to detect this error and prompt the user to
            // re-enter their credentials.  When you attempt to store the re-entered credentials
            // using storeUsername:andPassword:forServiceName:updateExisting:error
            // the old, incorrect entry will be deleted and a new one with a properly encrypted
            // password will be added.
            if (error != nil) {
                *error = [NSError errorWithDomain: KeychainWrapperErrorDomain code: -1999 userInfo: nil];
            }
        }
        else {
            // Something else went wrong. Simply return the normal Keychain API error code.
            if (error != nil) {
                *error = [NSError errorWithDomain: KeychainWrapperErrorDomain code: status userInfo: nil];
            }
        }

        return nil;
    }

    NSString *password = nil;   

    if (resultData) {
        password = [[NSString alloc] initWithData: resultData encoding: NSUTF8StringEncoding];
    }
    else {
        // There is an existing item, but we weren't able to get password data for it for some reason,
        // Possibly as a result of an item being incorrectly entered by the previous code.
        // Set the -1999 error so the code above us can prompt the user again.
        if (error != nil) {
            *error = [NSError errorWithDomain: KeychainWrapperErrorDomain code: -1999 userInfo: nil];
        }
    }

    return password;
}

+ (BOOL) storeUsername: (NSString *) username andPassword: (NSString *) password forServiceName: (NSString *) serviceName updateExisting: (BOOL) updateExisting error: (NSError **) error 
{       
    if (!username || !password || !serviceName) 
    {
        if (error != nil) 
        {
            *error = [NSError errorWithDomain: KeychainWrapperErrorDomain code: -2000 userInfo: nil];
        }
        return NO;
    }

    // See if we already have a password entered for these credentials.
    NSError *getError = nil;
    NSString *existingPassword = [KeychainWrapper getPasswordForUsername: username andServiceName: serviceName error:&getError];

    if ([getError code] == -1999) 
    {
        // There is an existing entry without a password properly stored (possibly as a result of the previous incorrect version of this code.
        // Delete the existing item before moving on entering a correct one.

        getError = nil;

        [self deleteItemForUsername: username andServiceName: serviceName error: &getError];

        if ([getError code] != noErr) 
        {
            if (error != nil) 
            {
                *error = getError;
            }
            return NO;
        }
    }
    else if ([getError code] != noErr) 
    {
        if (error != nil) 
        {
            *error = getError;
        }
        return NO;
    }

    if (error != nil) 
    {
        *error = nil;
    }

    OSStatus status = noErr;

    if (existingPassword) 
    {
        // We have an existing, properly entered item with a password.
        // Update the existing item.

        if (![existingPassword isEqualToString:password] && updateExisting) 
        {
            //Only update if we're allowed to update existing.  If not, simply do nothing.

            NSArray *keys = [[NSArray alloc] initWithObjects: (__bridge_transfer NSString *) kSecClass, 
                             kSecAttrService, 
                             kSecAttrLabel, 
                             kSecAttrAccount, 
                             nil];

            NSArray *objects = [[NSArray alloc] initWithObjects: (__bridge_transfer NSString *) kSecClassGenericPassword, 
                                serviceName,
                                serviceName,
                                username,
                                nil];

            NSDictionary *query = [[NSDictionary alloc] initWithObjects: objects forKeys: keys];            

            status = SecItemUpdate((__bridge_retained CFDictionaryRef) query, (__bridge_retained CFDictionaryRef) [NSDictionary dictionaryWithObject: [password dataUsingEncoding: NSUTF8StringEncoding] forKey: (__bridge_transfer NSString *) kSecValueData]);
        }
    }
    else 
    {
        // No existing entry (or an existing, improperly entered, and therefore now
        // deleted, entry).  Create a new entry.

        NSArray *keys = [[NSArray alloc] initWithObjects: (__bridge_transfer NSString *) kSecClass, 
                         kSecAttrService, 
                         kSecAttrLabel, 
                         kSecAttrAccount, 
                         kSecValueData, 
                         nil];

        NSArray *objects = [[NSArray alloc] initWithObjects: (__bridge_transfer NSString *) kSecClassGenericPassword, 
                            serviceName,
                            serviceName,
                            username,
                            [password dataUsingEncoding: NSUTF8StringEncoding],
                            nil];

        NSDictionary *query = [[NSDictionary alloc] initWithObjects: objects forKeys: keys];            

        status = SecItemAdd((__bridge_retained CFDictionaryRef) query, NULL);
    }

    if (error != nil && status != noErr) 
    {
        // Something went wrong with adding the new item. Return the Keychain error code.
        *error = [NSError errorWithDomain: KeychainWrapperErrorDomain code: status userInfo: nil];

        return NO;
    }

    return YES;
}

+ (BOOL) deleteItemForUsername: (NSString *) username andServiceName: (NSString *) serviceName error: (NSError **) error 
{
    if (!username || !serviceName) 
    {
        if (error != nil) 
        {
            *error = [NSError errorWithDomain: KeychainWrapperErrorDomain code: -2000 userInfo: nil];
        }
        return NO;
    }

    if (error != nil) 
    {
        *error = nil;
    }

    NSArray *keys = [[NSArray alloc] initWithObjects: (__bridge_transfer NSString *) kSecClass, kSecAttrAccount, kSecAttrService, kSecReturnAttributes, nil];
    NSArray *objects = [[NSArray alloc] initWithObjects: (__bridge_transfer NSString *) kSecClassGenericPassword, username, serviceName, kCFBooleanTrue, nil];

    NSDictionary *query = [[NSDictionary alloc] initWithObjects: objects forKeys: keys];

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

    if (error != nil && status != noErr) 
    {
        *error = [NSError errorWithDomain: KeychainWrapperErrorDomain code: status userInfo: nil];      

        return NO;
    }

    return YES;
}

#endif

@end

Answer 2

Here's an ARCified version that had successfully compiled for me. Just remember to link the Security Framework with your target.

Hope this helps!

Answer 3

Any references to CF classes must be paired with a "__bridge" statement to cast between Objective-C and Core Foundation Classes

Try this :

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