Minecraft-Console-Client/MinecraftClient/Crypto/AesContext.cs

using System;
using System.Runtime.CompilerServices;
using System.Runtime.InteropServices;
using System.Runtime.Intrinsics;
using System.Runtime.Intrinsics.X86;

namespace MinecraftClient.Crypto
{
    // Using the AES-NI instruction set
    // https://gist.github.com/Thealexbarney/9f75883786a9f3100408ff795fb95d85
    public class AesContext
    {
        private Vector128<byte>[] RoundKeys { get; }

        public byte[] Iv { get; } = new byte[0x10];

        public AesContext(Span<byte> key)
        {
            RoundKeys = KeyExpansion(key);
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining | MethodImplOptions.AggressiveOptimization)]
        public void EncryptEcb(ReadOnlySpan<byte> plaintext, Span<byte> destination)
        {
            Vector128<byte>[] keys = RoundKeys;

            ReadOnlySpan<Vector128<byte>> blocks = MemoryMarshal.Cast<byte, Vector128<byte>>(plaintext);
            Span<Vector128<byte>> dest = MemoryMarshal.Cast<byte, Vector128<byte>>(destination);

            // Makes the JIT remove all the other range checks on keys
            _ = keys[10];

            for (int i = 0; i < blocks.Length; i++)
            {
                Vector128<byte> b = blocks[i];

                b = Sse2.Xor(b, keys[0]);
                b = Aes.Encrypt(b, keys[1]);
                b = Aes.Encrypt(b, keys[2]);
                b = Aes.Encrypt(b, keys[3]);
                b = Aes.Encrypt(b, keys[4]);
                b = Aes.Encrypt(b, keys[5]);
                b = Aes.Encrypt(b, keys[6]);
                b = Aes.Encrypt(b, keys[7]);
                b = Aes.Encrypt(b, keys[8]);
                b = Aes.Encrypt(b, keys[9]);
                b = Aes.EncryptLast(b, keys[10]);

                dest[i] = b;
            }
        }

        private static Vector128<byte>[] KeyExpansion(Span<byte> key)
        {
            var keys = new Vector128<byte>[20];

            keys[0] = Unsafe.ReadUnaligned<Vector128<byte>>(ref key[0]);

            MakeRoundKey(keys, 1, 0x01);
            MakeRoundKey(keys, 2, 0x02);
            MakeRoundKey(keys, 3, 0x04);
            MakeRoundKey(keys, 4, 0x08);
            MakeRoundKey(keys, 5, 0x10);
            MakeRoundKey(keys, 6, 0x20);
            MakeRoundKey(keys, 7, 0x40);
            MakeRoundKey(keys, 8, 0x80);
            MakeRoundKey(keys, 9, 0x1b);
            MakeRoundKey(keys, 10, 0x36);

            for (int i = 1; i < 10; i++)
            {
                keys[10 + i] = Aes.InverseMixColumns(keys[i]);
            }

            return keys;
        }

        private static void MakeRoundKey(Vector128<byte>[] keys, int i, byte rcon)
        {
            Vector128<byte> s = keys[i - 1];
            Vector128<byte> t = keys[i - 1];

            t = Aes.KeygenAssist(t, rcon);
            t = Sse2.Shuffle(t.AsUInt32(), 0xFF).AsByte();

            s = Sse2.Xor(s, Sse2.ShiftLeftLogical128BitLane(s, 4));
            s = Sse2.Xor(s, Sse2.ShiftLeftLogical128BitLane(s, 8));

            keys[i] = Sse2.Xor(s, t);
        }

        public void SetIv(Span<byte> iv)
        {
            iv.Slice(0, 0x10).CopyTo(Iv);
        }
    }
}