Adding item to keychain using Swift

Question

I'm trying to add an item to the iOS keychain using Swift but can't figure out how to type cast properly. From WWDC 2013 session 709, given the following Objective-C code:

NSData *secret = [@"top secret" dataWithEncoding:NSUTF8StringEncoding];
NSDictionary *query = @{
    (id)kSecClass: (id)kSecClassGenericPassword,
    (id)kSecAttrService: @"myservice",
    (id)kSecAttrAccount: @"account name here",
    (id)kSecValueData: secret,
};

OSStatus = SecItemAdd((CFDictionaryRef)query, NULL);

Attempting to do it in Swift as follows:

var secret: NSData = "Top Secret".dataUsingEncoding(NSUTF8StringEncoding, allowLossyConversion: false)
var query: NSDictionary = [
    kSecClass: kSecClassGenericPassword,
    kSecAttrService: "MyService",
    kSecAttrAccount: "Some account",
    kSecValueData: secret
]

yields the error "Cannot convert the expression's type 'Dictionary' to 'DictionaryLiteralConvertible'.

Another approach I took was to use Swift and the - setObject:forKey: method on a Dictionary to add kSecClassGenericPassword with the key kSecClass.

In Objective-C:

NSMutableDictionary *searchDictionary = [NSMutableDictionary dictionary];
[searchDictionary setObject:(id)kSecClassGenericPassword forKey:(id)kSecClass];

In the Objective-C code, the CFTypeRef of the various keychain item class keys are bridged over using id. In the Swift documentation it's mentioned that Swift imports id as AnyObject. However when I attempted to downcast kSecClass as AnyObject for the method, I get the error that "Type 'AnyObject' does not conform to NSCopying.

Any help, whether it's a direct answer or some guidance about how to interact with Core Foundation types would be appreciated.

EDIT 2

This solution is no longer valid as of Xcode 6 Beta 2. If you are using Beta 1 the code below may work.

var secret: NSData = "Top Secret".dataUsingEncoding(NSUTF8StringEncoding, allowLossyConversion: false)
let query = NSDictionary(objects: [kSecClassGenericPassword, "MyService", "Some account", secret], forKeys: [kSecClass,kSecAttrService, kSecAttrAccount, kSecValueData])

OSStatus status = SecItemAdd(query as CFDictionaryRef, NULL)

To use Keychain Item Attribute keys as dictionary keys you have to unwrap them by using either takeRetainedValue or takeUnretainedValue (as appropriate). Then you can cast them to NSCopying. This is because they are CFTypeRefs in the header, which aren't all copyable.

As of Xcode 6 Beta 2 however, this causes Xcode to crash.

Answer 1

You simply need to downcast the literal:

let dict = ["hi": "Pasan"] as NSDictionary

Now dict is an NSDictionary. To make a mutable one, it's very similar to Objective-C:

let mDict = dict.mutableCopy() as NSMutableDictionary
mDict["hola"] = "Ben"

Answer 2

In the xcode 6.0.1 you must do this!!

let kSecClassValue = NSString(format: kSecClass)
let kSecAttrAccountValue = NSString(format: kSecAttrAccount)
let kSecValueDataValue = NSString(format: kSecValueData)
let kSecClassGenericPasswordValue = NSString(format: kSecClassGenericPassword)
let kSecAttrServiceValue = NSString(format: kSecAttrService)
let kSecMatchLimitValue = NSString(format: kSecMatchLimit)
let kSecReturnDataValue = NSString(format: kSecReturnData)
let kSecMatchLimitOneValue = NSString(format: kSecMatchLimitOne)

Answer 3

more convenient to use the cocoa pods SSKeychain

+ (NSArray *)allAccounts;
+ (NSArray *)accountsForService:(NSString *)serviceName;
+ (NSString *)passwordForService:(NSString *)serviceName account:(NSString *)account;
+ (BOOL)deletePasswordForService:(NSString *)serviceName account:(NSString *)account;
+ (BOOL)setPassword:(NSString *)password forService:(NSString *)serviceName account:(NSString *)account;

Answer 4

In order to get this to work, you need to access the retained values of the keychain constants instead. For example:

let kSecClassValue = kSecClass.takeRetainedValue() as NSString
let kSecAttrAccountValue = kSecAttrAccount.takeRetainedValue() as NSString
let kSecValueDataValue = kSecValueData.takeRetainedValue() as NSString
let kSecClassGenericPasswordValue = kSecClassGenericPassword.takeRetainedValue() as NSString
let kSecAttrServiceValue = kSecAttrService.takeRetainedValue() as NSString
let kSecMatchLimitValue = kSecMatchLimit.takeRetainedValue() as NSString
let kSecReturnDataValue = kSecReturnData.takeRetainedValue() as NSString
let kSecMatchLimitOneValue = kSecMatchLimitOne.takeRetainedValue() as NSString

You can then reference the values in the MSMutableDictionary like so:

var keychainQuery: NSMutableDictionary = NSMutableDictionary(objects: [kSecClassGenericPasswordValue, service, userAccount, kCFBooleanTrue, kSecMatchLimitOneValue], forKeys: [kSecClassValue, kSecAttrServiceValue, kSecAttrAccountValue, kSecReturnDataValue, kSecMatchLimitValue])

I wrote a blog post about it at: http://rshelby.com/2014/08/using-swift-to-save-and-query-ios-keychain-in-xcode-beta-4/

Hope this helps!

rshelby

Answer 5

Perhaps things have improved since. On Xcode 7 beta 4, no casting seems to be necessary except when dealing with the result AnyObject?. Specifically, the following seems to work:

var query : [NSString : AnyObject] = [
    kSecClass : kSecClassGenericPassword,
    kSecAttrService : "MyAwesomeService",
    kSecReturnAttributes : true,   // return dictionary in result parameter
    kSecReturnData : true          // include the password value
]
var result : AnyObject?
let err = SecItemCopyMatching(query, &result)
if (err == errSecSuccess) {
    // on success cast the result to a dictionary and extract the
    // username and password from the dictionary.
    if let result = result as ? [NSString : AnyObject],
       let username = result[kSecAttrAccount] as? String,
       let passdata = result[kSecValueData] as? NSData,
       let password = NSString(data:passdata, encoding:NSUTF8StringEncoding) as? String {
        return (username, password)
    }
} else if (status == errSecItemNotFound) {
    return nil;
} else {
    // probably a program error,
    // print and lookup err code (e.g., -50 = bad parameter)
}

To add a key if it was missing:

var query : [NSString : AnyObject] = [
    kSecClass : kSecClassGenericPassword,
    kSecAttrService : "MyAwesomeService",
    kSecAttrLabel : "MyAwesomeService Password",
    kSecAttrAccount : username,
    kSecValueData : password.dataUsingEncoding(NSUTF8StringEncoding)!
]
let result = SecItemAdd(query, nil)
// check that result is errSecSuccess, etc...

A few things to point out: your initial problem might have been that str.dataUsingEncoding returns an Optional. Adding '!' or better yet, using an if let to handle nil return, would likely make your code work. Printing out the error code and looking it up in the docs will help a lot in isolating the problem (I was getting err -50 = bad parameter, until I noticed a problem with my kSecClass, nothing to do with data types or casts!).

Answer 6

Swift 3

let kSecClassKey = String(kSecClass)
let kSecAttrAccountKey = String(kSecAttrAccount)
let kSecValueDataKey = String(kSecValueData)
let kSecClassGenericPasswordKey = String(kSecClassGenericPassword)
let kSecAttrServiceKey = String(kSecAttrService)
let kSecMatchLimitKey = String(kSecMatchLimit)
let kSecReturnDataKey = String(kSecReturnData)
let kSecMatchLimitOneKey = String(kSecMatchLimitOne)

you can also do it inside the dictionary itself alá:

var query: [String: Any] = [
    String(kSecClass): kSecClassGenericPassword,
    String(kSecAttrService): "MyService",
    String(kSecAttrAccount): "Some account",
    String(kSecValueData): secret
]

however, this is more expensive for the compiler, even more so since you're probably using the query in multiple places.