EncryptedString.cs

public class PlaceOrderCommand : ICommand
{
    public string BuyerId { get; set; }
    public Address Address { get; set; }
    public List<OrderItem> Items { get; set; }
    public CreditCardEncrypted CreditCard { get; set; }

    public class CreditCardEncrypted
    {
        public EncryptedString Number { get; set; }
        public EncryptedString Expiry { get; set; }
        public EncryptedString Cvv { get; set; }
    }
}