Swift iOS : KeyChain

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KeyChain提供了加密存储敏感信息的方法。所谓的敏感信息，不外是密码，信用卡号等。如果一个对象含有敏感信息，也可以把整个对象序列化为Data，然后整体存入KeyChain。对应的，也有从KeyChain中提取Data出来的操作。

然而，KeyChain默认提供的API是相当冗长和啰嗦的。而使用一些第三方库如KeyChainSwift又显得过于重量级。这里对KeyChain做了一个简单的封装，并提供了一个案例，可以把一个对象（User）存储到KeyChain内，并反向操作打印进入和出来的对象的结果。

对象是需要符合NSCoding协议的，以便可以序列化为Data对象，以及从Data对象内回复一个对象出来。代码改编于 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
    }
}

运行后，应该可以看到控制台上打印：

{id:1,name:tom} {id:1,name:tom}