the-cycle/src/Prospect.Server.Steam/AppTicket.cs

using System;
using System.Collections.Generic;
using System.IO;
using System.Net;

namespace Prospect.Server.Steam
{
    public class AppTicket
    {
        private AppTicket()
        {
            
        }

        /// <summary>
        ///     Full appticket, with a GC token and session header.
        /// </summary>
        public byte[] AuthTicket { get; set; }
        
        public ulong GcToken { get; set; }
        
        public DateTimeOffset TokenGenerated { get; set; }
        
        private IPAddress SessionExternalIp { get; set; }
        
        /// <summary>
        ///     Time the client has been connected to Steam in ms.
        /// </summary>
        public uint ClientConnectionTime { get; set; }
        
        /// <summary>
        ///     How many servers the client has connected to.
        /// </summary>
        public uint ClientConnectionCount { get; set; }
        
        public uint Version { get; set; }
        
        public ulong SteamId { get; set; }
        
        public uint AppId { get; set; }
        
        public IPAddress OwnershipTicketExternalIp { get; set; }
        
        public IPAddress OwnershipTicketInternalIp { get; set; }
        
        public uint OwnershipFlags { get; set; }
        
        public DateTimeOffset OwnershipTicketGenerated { get; set; }
        
        public DateTimeOffset OwnershipTicketExpires { get; set; }
        
        public List<uint> Licenses { get; set; }
        
        public List<AppDlc> Dlc { get; set; }

        public byte[] Signature { get; set; }
        
        public bool IsExpired { get; set; }
        
        public bool HasValidSignature { get; set; }
        
        public bool IsValid { get; set; }
        
        public static AppTicket Parse(string ticketHex)
        {
            var result = new AppTicket();
            var ticketBytes = Convert.FromHexString(ticketHex);

            using (var stream = new MemoryStream(ticketBytes))
            using (var ticketReader = new BinaryReader(stream))
            {
                // AuthTicket
                var initialLength = ticketReader.ReadUInt32();
                if (initialLength == 20)
                {
                    result.AuthTicket = ticketBytes.AsSpan(0, 52).ToArray();
                    result.GcToken = ticketReader.ReadUInt64();

                    ticketReader.BaseStream.Position += 8;

                    result.TokenGenerated = DateTimeOffset.FromUnixTimeSeconds(ticketReader.ReadUInt32());

                    if (ticketReader.ReadUInt32() != 24)
                    {
                        return null;
                    }

                    ticketReader.BaseStream.Position += 8;
                    
                    result.SessionExternalIp = new IPAddress(BitConverter.GetBytes(ticketReader.ReadUInt32()));
                    
                    ticketReader.BaseStream.Position += 4;

                    result.ClientConnectionTime = ticketReader.ReadUInt32();
                    result.ClientConnectionCount = ticketReader.ReadUInt32();

                    if (ticketReader.ReadUInt32() + ticketReader.BaseStream.Position != ticketReader.BaseStream.Length)
                    {
                        return null;
                    }
                }
                else
                {
                    ticketReader.BaseStream.Position -= 4;
                }
                
                // Ownership ticket
                var ownershipTicketOffset = ticketReader.BaseStream.Position;
                var ownershipTicketLength = ticketReader.ReadUInt32();
                if (ownershipTicketOffset + ownershipTicketLength != ticketReader.BaseStream.Length &&
                    ownershipTicketOffset + ownershipTicketLength + 128 != ticketReader.BaseStream.Length)
                {
                    return null;
                }

                result.Version = ticketReader.ReadUInt32();
                result.SteamId = ticketReader.ReadUInt64();
                result.AppId = ticketReader.ReadUInt32();
                result.OwnershipTicketExternalIp = new IPAddress(BitConverter.GetBytes(ticketReader.ReadUInt32()));
                result.OwnershipTicketInternalIp = new IPAddress(BitConverter.GetBytes(ticketReader.ReadUInt32()));
                result.OwnershipFlags = ticketReader.ReadUInt32();
                result.OwnershipTicketGenerated  = DateTimeOffset.FromUnixTimeSeconds(ticketReader.ReadUInt32());
                result.OwnershipTicketExpires  = DateTimeOffset.FromUnixTimeSeconds(ticketReader.ReadUInt32());
                result.Licenses = new List<uint>();

                var licenseCount = ticketReader.ReadUInt16();
                for (var i = 0; i < licenseCount; i++)
                {
                    result.Licenses.Add(ticketReader.ReadUInt32());
                }

                result.Dlc = new List<AppDlc>();
                
                var dlcCount = ticketReader.ReadUInt16();
                for (var i = 0; i < dlcCount; i++)
                {
                    var dlc = new AppDlc();

                    dlc.AppId = ticketReader.ReadUInt32();
                    dlc.Licenses = new List<uint>();

                    var dlcLicenseCount = ticketReader.ReadUInt16();
                    for (var j = 0; j < dlcLicenseCount; j++)
                    {
                        dlc.Licenses.Add(ticketReader.ReadUInt32());
                    }
                    
                    result.Dlc.Add(dlc);
                }

                ticketReader.ReadUInt16();

                if (ticketReader.BaseStream.Position + 128 == ticketReader.BaseStream.Length)
                {
                    result.Signature = ticketBytes.AsSpan((int)ticketReader.BaseStream.Position, 128).ToArray();
                }

                var date = DateTimeOffset.UtcNow;
                result.IsExpired = result.OwnershipTicketExpires < date;
                result.HasValidSignature = result.Signature != null && SteamCrypto.VerifySignature(ticketBytes.AsSpan((int)ownershipTicketOffset, (int)ownershipTicketLength).ToArray(), result.Signature);
                result.IsValid = !result.IsExpired && (result.Signature == null || result.HasValidSignature);
            }
            
            return result;
        }
    }
}