GeniusInvokationDecoding.cs

using System;
using System.Buffers.Binary;
using System.Text;

namespace GeniusInvokationEncoding;

/// <summary>
/// https://www.bilibili.com/video/av278125720
/// </summary>
internal class Program
{
    static unsafe void Main(string[] args)
    {
        // 51 bytes obfuscated data
        byte[] bytes = Convert.FromBase64String("BCHBwxQNAYERyVANCJGBynkOCZER2pgOCrFx8poQChGR9bYQDEGB9rkQDFKRD7oRDeEB");

        fixed(byte* ptr = bytes)
        {
            // Reinterpret as 50 byte actual data and 1 deobfuscate key byte
            EncodedData* data = (EncodedData*)ptr;
            byte* dataPtr = data->Data;

            // Prepare rearranged buffer
            RearrangedData rearranged = default;
            byte* pFirst = rearranged.First;
            byte* pSecond = rearranged.Second;
            for (int i = 0; i < 50; i++)
            {
                // Determine which half are we going to insert
                byte** ppTarget = i % 2 == 0 ? &pFirst : &pSecond;

                // (actual data =  data - key) and save it directly to the target half
                **ppTarget = unchecked((byte)(dataPtr[i] - data->DeobfuscateKey));

                (*ppTarget)++;
            }

            // Prepare decoded data result buffer
            DecodedData decoded = default;
            ushort* pDecoded = decoded.Data;

            // reinterpret as DecodeGroup for each 3 bytes
            DecodeGroup* pRearranged = (DecodeGroup*)&rearranged;
            for (int i = 0; i < 17; i++)
            {
                (ushort first, ushort second) = pRearranged->GetData();

                *pDecoded = first;
                *(pDecoded + 1) = second;

                pDecoded += 2;
                pRearranged++;
            }

            StringBuilder stringBuilder = new();
            for (int i = 0; i < 33; i++)
            {
                stringBuilder.AppendFormat("{0,3}", decoded.Data[i]).Append(',');

                if (i % 3 == 2)
                {
                    stringBuilder.Append('\n');
                }
            }

            Console.WriteLine(stringBuilder.ToString(0, stringBuilder.Length - 1));
        }
    }
}

public struct EncodedData
{
    public unsafe fixed byte Data[50];
    public byte DeobfuscateKey;
}

public struct RearrangedData
{
    public unsafe fixed byte First[25];
    public unsafe fixed byte Second[25];

    // Make RearrangedData 51 bytes
    // allow to be group as 17 DecodeGroups
    public byte padding; 
}

public struct DecodeGroup
{
    public unsafe fixed byte Data[3];
    public unsafe (ushort First, ushort Second) GetData()
    {
        fixed (byte* ptr = Data)
        {
            uint value = BinaryPrimitives.ReverseEndianness((*(uint*)ptr) & 0x00FFFFFF) >> 8; // keep low 24 bits only
            return ((ushort)((value >> 12) & 0x0FFF), (ushort)(value & 0x0FFF));
        }
    }
}

public struct DecodedData
{
    public unsafe fixed ushort Data[33];
}

Id 对照表 https://github.com/DGP-Studio/Snap.Metadata/blob/main/CheatTable/CHS/GcgDeckCard.csv