Swift iOS : KeyChain

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KeyChain提供了加密儲存敏感資訊的方法。所謂的敏感資訊，不外是密碼，信用卡號等。如果一個物件含有敏感資訊，也可以把整個物件序列化為Data，然後整體存入KeyChain。對應的，也有從KeyChain中提取Data出來的操作。

然而，KeyChain預設提供的API是相當冗長和囉嗦的。而使用一些第三方庫如KeyChainSwift又顯得過於重量級。這裡對KeyChain做了一個簡單的封裝，並提供了一個案例，可以把一個物件（User）儲存到KeyChain內，並反向操作列印進入和出來的物件的結果。

物件是需要符合NSCoding協議的，以便可以序列化為Data物件，以及從Data物件內回覆一個物件出來。程式碼改編於 gist.github.com/s-aska/e7ad…

import UIKit
@UIApplicationMain
class AppDelegate: UIResponder, UIApplicationDelegate {
    var window: UIWindow?
    func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey: Any]?) -> Bool {
        let user = User(1,"tom")
        user.saveToKC()
        let user1 = User.loadFromKC()
        print(user,user1)
        return true
    }
}
class User : NSObject,NSCoding{
    var id : Int32
    var name : String
    init(_ id: Int32 ,_ name : String) {
        self.id = id
        self.name = name
    }
    required convenience init?(coder decoder: NSCoder) {
        guard let id = decoder.decodeInt32(forKey: "id") as? Int32,
            let name = decoder.decodeObject(forKey:"name") as? String
            else { return nil }

        self.init(id,name)
    }
    func encode(with coder: NSCoder) {
        coder.encode(self.id, forKey: "id")
        coder.encode(self.name, forKey: "name")
    }
    override public var description: String { return "{id:\(id),name:\(name)}" }
    func saveToKC(){
        let data = NSKeyedArchiver.archivedData(withRootObject: self)
        _ = Keychain.save(key: "user", data: data)
    }
    class func loadFromKC()-> User{
        let data = Keychain.load(key: "user")
        return  NSKeyedUnarchiver.unarchiveObject(with: data!) as! User
    }
}
import UIKit
import Security
class Keychain {
    class func save(key: String, data: Data) -> Bool {
        let query = [
            kSecClass as String       : kSecClassGenericPassword as String,
            kSecAttrAccount as String : key,
            kSecValueData as String   : data ] as [String : Any]
        SecItemDelete(query as CFDictionary)
        let status: OSStatus = SecItemAdd(query as CFDictionary, nil)
        return status == noErr
    }
    class func load(key: String) -> Data? {
        let query = [
            kSecClass as String       : kSecClassGenericPassword,
            kSecAttrAccount as String : key,
            kSecReturnData as String  : kCFBooleanTrue,
            kSecMatchLimit as String  : kSecMatchLimitOne ] as [String : Any]
        var dataTypeRef: AnyObject?
        let status = withUnsafeMutablePointer(to: &dataTypeRef) { SecItemCopyMatching(query as CFDictionary, UnsafeMutablePointer($0)) }

        if status == errSecSuccess {
            if let data = dataTypeRef as! Data? {
                return data
            }
        }
        return nil
    }
    class func delete(key: String) -> Bool {
        let query = [
            kSecClass as String       : kSecClassGenericPassword,
            kSecAttrAccount as String : key ] as [String : Any]

        let status: OSStatus = SecItemDelete(query as CFDictionary)
        return status == noErr
    }
    class func clear() -> Bool {
        let query = [ kSecClass as String : kSecClassGenericPassword ]
        let status: OSStatus = SecItemDelete(query as CFDictionary)
        return status == noErr
    }
}複製程式碼

執行後，應該可以看到控制檯上列印：

{id:1,name:tom} {id:1,name:tom}複製程式碼