ChallengeResponse.cs

using OSDP.Net.Messages;
using System;
using OSDP.Net.Messages.SecureChannel;
 
namespace OSDP.Net.Model.ReplyData
{
    internal class ChallengeResponse : PayloadData
    {
        public ChallengeResponse(byte[] cUID, byte[] rndB, byte[] cryptogram, bool isUsingDefaultKey)
        {
            ClientUID = cUID;
            RndB = rndB;
            Cryptogram = cryptogram;
            IsUsingDefaultKey = isUsingDefaultKey;
        }

        public byte[] ClientUID {get; }

        public byte[] RndB { get; }

        public byte[] Cryptogram { get; }
 
        public bool IsUsingDefaultKey { get; }

        public static ChallengeResponse ParseData(ReadOnlySpan<byte> data, bool isDefaultKey)
        {
            if (data.Length != 32)
            {
                throw new InvalidPayloadException($"Challenge response must be 32 bytes, received {data.Length}");
            }
            
            return new ChallengeResponse(
                data.Slice(0, 8).ToArray(),
                data.Slice(8, 8).ToArray(),
                data.Slice(16, 16).ToArray(),
                isDefaultKey
            );
        }

        public override byte[] BuildData()
        {
            var payload = new byte[ClientUID.Length + RndB.Length + Cryptogram.Length];
            ClientUID.CopyTo(payload, 0);
            RndB.CopyTo(payload, ClientUID.Length);
            Cryptogram.CopyTo(payload, ClientUID.Length + RndB.Length);
 
            return payload;
        }
        
        public override byte Code => (byte)ReplyType.CrypticData;
        
        public override bool IsSecurityInitialization => true;
        
        public override ReadOnlySpan<byte> SecurityControlBlock()
        {
            return new byte[]
            {
                0x03,
                (byte)SecurityBlockType.SecureConnectionSequenceStep2,
                (byte)(IsUsingDefaultKey ? 0x00 : 0x01)
            };
        }
    }
}