objective c - Adding private key into iOS Keychain

Question

I am trying to add a private key into the iOS keychain. The certificate (public key) works fine but the private key refuses... I am totally confused why the following code does not work.

First I am checking if the current key (=key in case of that the Keychain is a key/value store) is 'free' in the Keychain. Then I am going to add the private key.

CFStringRef labelstring = CFStringCreateWithCString(NULL, [key cStringUsingEncoding:NSUTF8StringEncoding], kCFStringEncodingUTF8);

NSArray* keys = [NSArray arrayWithObjects:(__bridge id)kSecClass,kSecAttrLabel,kSecReturnData,kSecAttrAccessible,nil];
NSArray* values = [NSArray arrayWithObjects:(__bridge id)kSecClassKey,labelstring,kCFBooleanTrue,kSecAttrAccessibleWhenUnlocked,nil];
NSMutableDictionary* searchdict = [NSMutableDictionary dictionaryWithObjects:values forKeys:keys];

CFRelease(labelstring);

NSMutableDictionary *query = searchdict;


CFTypeRef item = NULL;
OSStatus error = SecItemCopyMatching((__bridge_retained CFDictionaryRef) query, &item);

if (error)
{
    NSLog(@"Error: %ld (statuscode)", error);
}

if(error != errSecItemNotFound)
{
    SecItemDelete((__bridge_retained CFDictionaryRef) query);
}

[query setObject:(id)data forKey:(__bridge id)kSecValueData];

OSStatus status = SecItemAdd((__bridge_retained CFDictionaryRef) query, &item);

if(status)
{
    NSLog(@"Keychain error occured: %ld (statuscode)", status);
    return NO;
}

The debug output is the following:

2012-07-26 15:33:03.772 App[15529:1b03] Error: -25300 (statuscode)
2012-07-26 15:33:11.195 App[15529:1b03] Keychain error occured: -25299 (statuscode)

The first error code -25300 represents errSecItemNotFound. So there is no value stored for this key. Then, when I try to add the private key into the Keychain I get -25299 which means errSecDuplicateItem. I do not understand this. Why is this happening?

Does anyone have a clue or hint on this?

Apple's error codes:

errSecSuccess                = 0,       /* No error. */
errSecUnimplemented          = -4,      /* Function or operation not implemented. */
errSecParam                  = -50,     /* One or more parameters passed to a function where not valid. */
errSecAllocate               = -108,    /* Failed to allocate memory. */
errSecNotAvailable           = -25291,  /* No keychain is available. You may need to restart your computer. */
errSecDuplicateItem          = -25299,  /* The specified item already exists in the keychain. */
errSecItemNotFound           = -25300,  /* The specified item could not be found in the keychain. */
errSecInteractionNotAllowed  = -25308,  /* User interaction is not allowed. */
errSecDecode                 = -26275,  /* Unable to decode the provided data. */
errSecAuthFailed             = -25293,  /* The user name or passphrase you entered is not correct. */ 

Thanks in advance!

Update #1: I've figured out that it works only for the first time. Even when data and key is different, after the first time stored into the keychain I cannot store further keys.

Answer 1

The following code worked for me:

NSMutableDictionary *query = [[NSMutableDictionary alloc] init]; 
[query setObject:(id)kSecClassKey forKey:(id)kSecClass]; 
[query setObject:(id)kSecAttrAccessibleWhenUnlocked forKey:(id)kSecAttrAccessible]; 
[query setObject:[NSNumber numberWithBool:YES] forKey:(id)kSecReturnData];

//adding access key 
[query setObject:(id)key forKey:(id)kSecAttrApplicationTag];


//removing item if it exists 
SecItemDelete((CFDictionaryRef)query);

//setting data (private key) 
[query setObject:(id)data forKey:(id)kSecValueData];

CFTypeRef persistKey; OSStatus status = SecItemAdd((CFDictionaryRef)query, &persistKey);

if(status) {
    NSLog(@"Keychain error occured: %ld (statuscode)", status);
    return NO; 
}