Dismiss TouchID authentication

[Vabs28]

Hi

I am not sure if this is possible.
Can we cancel TouchID authentication happening on decrypt operation if we dont want to proceed?
LAContext has a method "invalidate" which invalidates LAContext and throws LAErrorAppCancel error.

e.g. We prompt user to authenticate using TouchID as soon as app is opened. We also make a background call to check if user is running on latest app.
If user is running on old version then we cancel TouchID operation and show a message which says "Please update app to latest version."

[hfossli]

I’m really not sure. https://youtu.be/fpaQpyU_QiM

[hfossli]

Why do you want to cancel? What is the use case?

[Vabs28]

e.g. We prompt the user to authenticate using TouchID as soon as the app is opened. The app may also receive some authentication messages that he needs to action (select Accept/Reject on 2FA messages).

If the app receives an Authentication messages then we cancel the TouchID operation and show the authentication message.

[hfossli]

I have rewritten some of the code so I'm now able to pass a LAContext to sign and decrypt. Sad thing is that I don't get to dismiss the LAContext once it is showing the fingerprint dialog. Do you know how?

Example

import UIKit
import LocalAuthentication

class ViewController: UIViewController {

    var context: LAContext! = LAContext()
    
    func createAccessControl(protection: CFString = kSecAttrAccessibleWhenPasscodeSetThisDeviceOnly, flags: SecAccessControlCreateFlags = [.userPresence, .privateKeyUsage]) -> SecAccessControl {
        var error: Unmanaged<CFError>?
        let accessControl = SecAccessControlCreateWithFlags(kCFAllocatorDefault, protection, flags, &error)
        return accessControl!
    }
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        delay(1.0, queue: .main) {
            self.decrypt()
        }
    }
    
    func decrypt() {
        
        let accessControl = createAccessControl()
        context.evaluateAccessControl(accessControl, operation: .useKeySign, localizedReason: "Sign") { (success, error) in
            DispatchQueue.main.async {
                if success {
                    let alert = UIAlertController(title: "Authenticated", message: "Ready to sign/decrypt", preferredStyle: .alert)
                    alert.addAction(UIAlertAction(title: "OK", style: .cancel, handler: nil))
                    self.show(alert, sender: nil)
                } else {
                    let alert = UIAlertController(title: "Failed to authenticate", message: "Error: \(error!)", preferredStyle: .alert)
                    alert.addAction(UIAlertAction(title: "OK", style: .cancel, handler: nil))
                    self.show(alert, sender: nil)
                }
            }
        }
        
        delay(3.0, queue: .main) {
            self.context.invalidate()
        }
    }
}

func delay( _ delay: Double, queue: DispatchQueue, completion: @escaping () -> () ) {
    queue.asyncAfter(deadline: DispatchTime.now() + Double(Int64(delay * Double(NSEC_PER_SEC))) / Double(NSEC_PER_SEC)) { () -> Void in
        completion()
    }
}

It doesn't seem promising.

[hfossli]

If you are able to remove the dialog then I'll be happy to finish the rewrite to support LAContext.

[Vabs28]

Hi
I am new to Swift development.
I also tried similar thing, it doesn't close TouchID dialog.
Rather calling invalidate method doesn't do anything, you can still authenticate yourself with correct fingerprint.

[hfossli]

So then I guess this is not possible... sadly. If you find a way to close it I’ll be more than happy to change the library

[hfossli]

I have pushed my code to master. Whenever you sign or decrypt you will have the possibility of passing a LAContext.

Like this

let signature = try manager.sign(digest, authenticationContext: context)

[hfossli]

In this archive you'll find two files and you'll see there's a bug with LAContext

Bug.zip

[Vabs28]

Thanks a lot

[hfossli]

http://www.openradar.me/35069937

[hfossli]

Apple thinks this is fixed in latest GM. Are you, @Vabs28, able to check this?

[hfossli]

It seems apple solved this when working with the LAContext directly. It doesn't work for me when the LAContext is presented by Security framework for some reason.