Conforming to the NSSecureCoding protocol indicates that an object handles encoding and decoding instances of itself in a manner that is robust against object substitution attacks.

    protocol NSSecureCoding : NSCoding

    Historically, many classes decoded instances of themselves like this:

    if let object = decoder.decodeObject(forKey: "myKey") as? MyClass {
    } else {

    This technique is potentially unsafe because by the time you can verify the class type, the object has already been constructed, and if this is part of a collection class, potentially inserted into an object graph.

    In order to conform to NSSecureCoding:

    • An object that does not override init(coder:) can conform to NSSecureCoding without any changes (assuming that it is a subclass of another class that conforms).

    • An object that does override init(coder:) must decode any enclosed objects using the decodeObject(of:forKey:) method. For example:

      let obj = decoder.decodeObject(of: MyClass.self, forKey: "myKey")

      In addition, the class must override its NSSecureCoding method to return true.


    • protocol NSCoding

      The NSCoding protocol declares the two methods that a class must implement so that instances of that class can be encoded and decoded. This capability provides the basis for archiving (where objects and other structures are stored on disk) and distribution (where objects are copied to different address spaces).