Storing CryptoKit Keys in the Keychain

At a glance

Project structure

Source bundle/
├── CryptoKitKeychain/
│   ├── AppDelegate.swift
│   └── SceneDelegate.swift
├── CryptoKitKeychainMac/
│   └── AppDelegate.swift
├── Testing/
│   └── KeyTest.swift
├── Views/
│   ├── ContentView.swift
│   ├── CurveView.swift
│   ├── NISTView.swift
│   ├── SymmetricView.swift
│   └── ExecutionView.swift
└── Storage/
    ├── GenericPasswordStore.swift
    ├── SecKeyStore.swift
    └── GenericPasswordConvertible.swift

Structure observations

• Architecturally prominent files are ranked from entry points and role-named declarations; resource-only paths are omitted.
• Primary languages: Swift.
• The verified tree contains 8 project/configuration file(s) and 19 source declaration(s).

Overall architecture

flowchart LR
    Bundle["Sample bundle"]
    V1["CryptoKitKeychain"]
    V2["CryptoKitKeychainMac"]
    Boundary["CryptoKit APIs"]
    Bundle --> V1
    V1 --> Boundary
    Bundle --> V2
    V2 --> Boundary

Reference code

CryptoKitKeychain/AppDelegate.swift:10 — architecture anchor

@UIApplicationMain
class AppDelegate: UIResponder, UIApplicationDelegate { }

Interpretation

The branches represent separate entry-bearing project variants in the downloaded bundle, not runtime calls between those variants. Each branch is intentionally collapsed at the documented framework boundary; the detailed target-local flow remains in the cited files. Ownership is claimed only where the next section cites a stored property or assignment.

Ownership and state

classDiagram
    AppDelegate o-- NSWindow : window
    ContentView o-- KeyTest : tester
    CurveView o-- KeyTest : tester
    NISTView o-- KeyTest : tester

Ownership evidence

CryptoKitKeychainMac/AppDelegate.swift:14 — stored dependency or nearest verified ownership anchor

@NSApplicationMain
class AppDelegate: NSObject, NSApplicationDelegate {
    // ...
    var window: NSWindow!
    // ...
}

Composition arrows indicate a source-visible construction expression or locally owned value state; aggregation means the owner stores or receives a dependency without proving exclusive lifetime ownership.

Class and protocol design

Storage/GenericPasswordConvertible.swift:12 — representative type boundary

protocol GenericPasswordConvertible: CustomStringConvertible {
    /// Creates a key from a generic key representation.
    init<D>(genericKeyRepresentation data: D) throws where D: ContiguousBytes
    
    /// A generic representation of the key.
    var genericKeyRepresentation: SymmetricKey { get }
}

The source explicitly defines local protocol relationships: Curve25519.KeyAgreement.PrivateKey → GenericPasswordConvertible, Curve25519.Signing.PrivateKey → GenericPasswordConvertible, SymmetricKey → GenericPasswordConvertible, SecureEnclave.P256.KeyAgreement.PrivateKey → GenericPasswordConvertible, SecureEnclave.P256.Signing.PrivateKey → GenericPasswordConvertible, P256.Signing.PrivateKey → SecKeyConvertible.

Access control

Reference code

Storage/GenericPasswordConvertible.swift:23 — representative boundary

    public var description: String {
        return self.genericKeyRepresentation.withUnsafeBytes { bytes in
            return "Key representation contains \(bytes.count) bytes."
        }
    }

Swift declarations without a modifier are internal; explicit private, fileprivate, private(set), public, or open entries above are interpreted by language semantics. Objective-C/C samples instead rely on header and implementation boundaries, which are not equivalent to Swift lexical privacy.

Logic ownership and placement

Design patterns

Naming conventions

• Types: Delegate: AppDelegate, SceneDelegate; Store: GenericPasswordStore, SecKeyStore; View: ContentView, CurveView, ExecutionView, NISTView, SymmetricView.
• Protocols: GenericPasswordConvertible, SecKeyConvertible.
• Methods: applicationDidFinishLaunching, reset, run, scene.
• Files: CryptoKitKeychain/AppDelegate.swift, CryptoKitKeychainMac/AppDelegate.swift, Testing/KeyTest.swift, Views/ContentView.swift, Views/CurveView.swift, Views/NISTView.swift.

Architecture takeaways

• AppDelegate is the main source-visible entry or composition anchor for this sample.
• Framework work reaches CryptoKit, SwiftUI, Security, UIKit through a deliberately small high-level chain; the detailed API graph remains inside the cited implementation files.
• Stored-property evidence identifies lifecycle collaboration; it does not by itself prove exclusive object ownership.
• Access-control conclusions separate verified language visibility from the likely design rationale.
• Local protocol relationships provide an explicit substitution boundary.

Source map

• Official Apple documentation