public final class ClosedGroupSenderKey : NSObject, NSCoding { // NSObject/NSCoding conformance is needed for YapDatabase compatibility
    public let chainKey: Data
    public let keyIndex: UInt
    public let publicKey: Data

    // MARK: Initialization
    public init(chainKey: Data, keyIndex: UInt, publicKey: Data) {
        self.chainKey = chainKey
        self.keyIndex = keyIndex
        self.publicKey = publicKey
    }

    // MARK: Coding
    public init?(coder: NSCoder) {
        guard let chainKey = coder.decodeObject(forKey: "chainKey") as? Data,
            let keyIndex = coder.decodeObject(forKey: "keyIndex") as? UInt,
            let publicKey = coder.decodeObject(forKey: "publicKey") as? Data else { return nil }
        self.chainKey = chainKey
        self.keyIndex = UInt(keyIndex)
        self.publicKey = publicKey
        super.init()
    }

    public func encode(with coder: NSCoder) {
        coder.encode(chainKey, forKey: "chainKey")
        coder.encode(keyIndex, forKey: "keyIndex")
        coder.encode(publicKey, forKey: "publicKey")
    }

    // MARK: Equality
    override public func isEqual(_ other: Any?) -> Bool {
        guard let other = other as? ClosedGroupSenderKey else { return false }
        return chainKey == other.chainKey && keyIndex == other.keyIndex && publicKey == other.publicKey
    }

    // MARK: Hashing
    override public var hash: Int { // Override NSObject.hash and not Hashable.hashValue or Hashable.hash(into:)
        return chainKey.hashValue ^ keyIndex.hashValue ^ publicKey.hashValue
    }

    // MARK: Description
    override public var description: String {
        return "[ chainKey : \(chainKey), keyIndex : \(keyIndex), publicKey: \(publicKey.toHexString()) ]"
    }
}