diff --git a/src/NosCore.ParserInputGenerator/Extractor/NosArchive.cs b/src/NosCore.ParserInputGenerator/Extractor/NosArchive.cs
new file mode 100644
index 0000000..0ed48b7
--- /dev/null
+++ b/src/NosCore.ParserInputGenerator/Extractor/NosArchive.cs
@@ -0,0 +1,152 @@
+using System;
+using System.Collections.Generic;
+using System.IO;
+using System.Text;
+
+namespace NosCore.ParserInputGenerator.Extractor;
+
+/// <summary>
+/// Read/write support for the legacy NosTale <c>.NOS</c> archive format used
+/// by <c>NScliData_*.NOS</c> and friends. The newer "NT Data" DEFLATE variant
+/// is not supported — not needed for the NosMall URL patch since conststring
+/// archives use the legacy layout.
+///
+/// Layout: <c>int32 fileCount</c>, then per entry
+/// <c>int32 id; int32 nameLen; byte[nameLen] name; int32 unknown; int32 encLen; byte[encLen] enc</c>.
+/// The inner content is XOR-obfuscated — see <see cref="Decrypt"/> and
+/// <see cref="Encrypt"/> (our encrypter uses only the simple 0x33-XOR mode,
+/// which the decrypter handles along with the packed-nibble mode from the
+/// real client).
+/// </summary>
+public static class NosArchive
+{
+    /// <summary>
+    /// A single file entry inside a legacy <c>.NOS</c> archive.
+    /// </summary>
+    /// <param name="Id">Per-entry id stored in the archive header (usually the sequential index).</param>
+    /// <param name="Name">Inner file name (ASCII), e.g. <c>conststring.dat</c>.</param>
+    /// <param name="Unknown">The 4-byte header field between the name and the payload size whose purpose we don't yet characterise — preserve verbatim on round-trip.</param>
+    /// <param name="Content">Decrypted payload bytes.</param>
+    public sealed record Entry(int Id, string Name, int Unknown, byte[] Content);
+
+    private static readonly byte[] CryptoArray =
+    {
+        0x00, 0x20, 0x2D, 0x2E, 0x30, 0x31, 0x32, 0x33, 0x34,
+        0x35, 0x36, 0x37, 0x38, 0x39, 0x0A, 0x00,
+    };
+
+    /// <summary>
+    /// Parse a legacy <c>.NOS</c> archive and return its entries with
+    /// decrypted <see cref="Entry.Content"/>.
+    /// </summary>
+    public static List<Entry> Read(byte[] bytes)
+    {
+        var result = new List<Entry>();
+        var i = 0;
+        var fileCount = BitConverter.ToInt32(bytes, i); i += 4;
+        for (var f = 0; f < fileCount; f++)
+        {
+            var id = BitConverter.ToInt32(bytes, i); i += 4;
+            var nameLen = BitConverter.ToInt32(bytes, i); i += 4;
+            var name = Encoding.ASCII.GetString(bytes, i, nameLen);
+            i += nameLen;
+            var unknown = BitConverter.ToInt32(bytes, i); i += 4;
+            var encLen = BitConverter.ToInt32(bytes, i); i += 4;
+            var enc = new byte[encLen];
+            Buffer.BlockCopy(bytes, i, enc, 0, encLen);
+            i += encLen;
+            var content = Decrypt(enc);
+            result.Add(new Entry(id, name, unknown, content));
+        }
+        return result;
+    }
+
+    /// <summary>
+    /// Serialise a list of entries back to the legacy <c>.NOS</c> byte layout,
+    /// re-applying the simple 0x33-XOR encryption. The decrypter in the real
+    /// client accepts this output.
+    /// </summary>
+    public static byte[] Write(IReadOnlyList<Entry> entries)
+    {
+        using var ms = new MemoryStream();
+        using var w = new BinaryWriter(ms);
+        w.Write(entries.Count);
+        foreach (var e in entries)
+        {
+            var nameBytes = Encoding.ASCII.GetBytes(e.Name);
+            var enc = Encrypt(e.Content);
+            w.Write(e.Id);
+            w.Write(nameBytes.Length);
+            w.Write(nameBytes);
+            w.Write(e.Unknown);
+            w.Write(enc.Length);
+            w.Write(enc);
+        }
+        return ms.ToArray();
+    }
+
+    private static byte[] Decrypt(byte[] enc)
+    {
+        var output = new List<byte>(enc.Length * 2);
+        var i = 0;
+        while (i < enc.Length)
+        {
+            var b = enc[i++];
+            if (b == 0xFF)
+            {
+                output.Add(0x0D);
+                continue;
+            }
+            var len = b & 0x7F;
+            if ((b & 0x80) != 0)
+            {
+                for (; len > 0; len -= 2)
+                {
+                    if (i >= enc.Length) break;
+                    var c = enc[i++];
+                    output.Add(CryptoArray[(c & 0xF0) >> 4]);
+                    if (len <= 1) break;
+                    var lo = CryptoArray[c & 0x0F];
+                    if (lo == 0) break;
+                    output.Add(lo);
+                }
+            }
+            else
+            {
+                for (; len > 0; len--)
+                {
+                    if (i >= enc.Length) break;
+                    output.Add((byte)(enc[i++] ^ 0x33));
+                }
+            }
+        }
+        return output.ToArray();
+    }
+
+    private static byte[] Encrypt(byte[] plain)
+    {
+        using var ms = new MemoryStream(plain.Length * 2);
+        var i = 0;
+        while (i < plain.Length)
+        {
+            if (plain[i] == 0x0D)
+            {
+                ms.WriteByte(0xFF);
+                i++;
+                continue;
+            }
+            var start = i;
+            while (i < plain.Length && plain[i] != 0x0D && (i - start) < 0x7F)
+            {
+                i++;
+            }
+            var chunkLen = i - start;
+            ms.WriteByte((byte)chunkLen);
+            for (var j = start; j < i; j++)
+            {
+                ms.WriteByte((byte)(plain[j] ^ 0x33));
+            }
+        }
+        return ms.ToArray();
+    }
+}
diff --git a/src/NosCore.ParserInputGenerator/NosCore.ParserInputGenerator.csproj b/src/NosCore.ParserInputGenerator/NosCore.ParserInputGenerator.csproj
index 0314e49..6125ad7 100644
--- a/src/NosCore.ParserInputGenerator/NosCore.ParserInputGenerator.csproj
+++ b/src/NosCore.ParserInputGenerator/NosCore.ParserInputGenerator.csproj
@@ -12,7 +12,7 @@
 		<RepositoryUrl>https://github.com/NosCoreIO/NosCore.ParserInputGenerator.git</RepositoryUrl>
 		<PackageIconUrl></PackageIconUrl>
 		<PackageTags>nostale, noscore, nostale private server source, nostale emulator</PackageTags>
-		<Version>4.0.0</Version>
+		<Version>4.1.0</Version>
 		<PackageRequireLicenseAcceptance>false</PackageRequireLicenseAcceptance>
 		<Description>NosCore's Parser InputGenerator</Description>
 		<PackageLicenseExpression></PackageLicenseExpression>