iOS Keychain occasionally return empty string - iphone

Question

I write very secure application (for Bank) and I keep the private key in the Keychain.
I keep the Private key using the following code:
+(void)savePrivatekey:(NSString *)Key
{
KeychainItemWrapper *keychain = [[KeychainItemWrapper alloc] initWithIdentifier:#"pKey" accessGroup:nil];
[keychain setObject:Key forKey:(id)kSecValueData];
[keychain release];
}
and for get the private key using the following code:
+(NSString *)privateKey
{
KeychainItemWrapper *keychain = [[KeychainItemWrapper alloc] initWithIdentifier:#"pKey"accessGroup:nil];
NSString *privateKey = [keychain objectForKey:(id)kSecValueData];
[keychain release];
return privateKey;
}
i don't save the private key in local variable from security reasons.
because every call to server I need the private key i call to to function
"GetPrivateKey" a lot of times.
Maybe that's why sometimes i get from the keychain empty string.
i can't think of why this might happen.
I noticed that in most cases this happens when the application return from background but no only...
thanks...
I opened ticket at Apple's engineers and they responded to me:
Are you setting the kSecAttrAccessible attribute when you create the keychain item initially?
I always create the same shape keychain:
KeychainItemWrapper * keychain = [[KeychainItemWrapper alloc] initWithIdentifier: # "pKey" accessGroup: nil];
Does anyone know what their intent?
thanks...

Answer 1

I answered my own question a while back regarding this. I'm not sure if this is your exact problem as your code seems to look/work fine. So regarding your keychain access, I'm guessing it is a bit different. This may or may not help, but might steer you in the right direction.
iOS KeyChain not retrieving values from background

Answer 2

If your class is using ARC the following works for me every time.
KeychainItemWrapper *testKeychain = [[KeychainItemWrapper alloc] initWithIdentifier:#"AppUniqueID" accessGroup:nil];
NSString *privateKey = [testKeychain objectForKey:(__bridge id)(kSecValueData)];
NSLog(#"Private Key: %# \n", privateKey);