SupportsSecureCoding

SupportsSecureCoding is a class-level indicator used in the Apple Foundation framework to denote that a class supports secure coding for archiving and unarchiving. It is associated with the NSSecureCoding protocol, which aims to prevent object substitution attacks by ensuring that decoded data matches expected classes.

In Objective-C, a class conforming to NSSecureCoding implements a class method named supportsSecureCoding that returns a boolean value. Returning YES (true) signals that the class fully supports secure coding and will perform type-checked decoding. A typical implementation looks like: + (BOOL)supportsSecureCoding { return YES; } The class then provides encodeWithCoder: and initWithCoder: methods to perform secure encoding and decoding.

In Swift, conforming to NSSecureCoding requires implementing a static property supportsSecureCoding: Bool { get }. A conforming type also implements encode(with:) and a required init?(coder:) to handle the secure decoding. A minimal Swift example is: class MyObject: NSObject, NSSecureCoding { static var supportsSecureCoding: Bool { return true } func encode(with coder: NSCoder) { ... } required init?(coder: NSCoder) { ... } }

Secure coding affects decoding by encouraging or enforcing the use of methods that validate the class type, such as decodeObjectOfClass:forKey: and decodeObjectOfClasses:forKey:, or their Swift equivalents. It also interacts with NSKeyedUnarchiver options to require secure coding during unarchiving.

Best practices include adopting NSSecureCoding for persisted or transmitted objects, explicitly declaring supportsSecureCoding, and using secure decoding APIs to specify permissible classes. If a class cannot perform secure decoding, it should not conform to NSSecureCoding. This approach helps reduce security risks during data restoration and interprocess data transfer.