diff --git a/SabreTools.Models/VPK/ArchiveMD5SectionEntry.cs b/SabreTools.Models/VPK/ArchiveMD5SectionEntry.cs
new file mode 100644
index 0000000..c726dff
--- /dev/null
+++ b/SabreTools.Models/VPK/ArchiveMD5SectionEntry.cs
@@ -0,0 +1,27 @@
+using System.Runtime.InteropServices;
+
+namespace SabreTools.Models.VPK
+{
+    /// <see href="https://developer.valvesoftware.com/wiki/VPK_(file_format)"/>
+    [StructLayout(LayoutKind.Sequential)]
+    public sealed class ArchiveMD5SectionEntry
+    {
+        public uint ArchiveIndex;
+
+        /// <summary>
+        /// Where to start reading bytes
+        /// </summary>
+        public uint StartingOffset;
+
+        /// <summary>
+        /// How many bytes to check
+        /// </summary>
+        public uint Count;
+
+        /// <summary>
+        /// Expected checksum
+        /// </summary>
+        [MarshalAs(UnmanagedType.ByValArray, SizeConst = 16)]
+        public byte[]? MD5Checksum = new byte[16];
+    }
+}
\ No newline at end of file
diff --git a/SabreTools.Models/VPK/DirectoryEntry.cs b/SabreTools.Models/VPK/DirectoryEntry.cs
index 0412469..4b8a789 100644
--- a/SabreTools.Models/VPK/DirectoryEntry.cs
+++ b/SabreTools.Models/VPK/DirectoryEntry.cs
@@ -3,17 +3,37 @@ using System.Runtime.InteropServices;
 namespace SabreTools.Models.VPK
 {
     /// <see href="https://github.com/RavuAlHemio/hllib/blob/master/HLLib/VPKFile.h"/>
+    /// <see href="https://developer.valvesoftware.com/wiki/VPK_(file_format)"/>
     [StructLayout(LayoutKind.Sequential)]
     public sealed class DirectoryEntry
     {
+        /// <summary>
+        /// A 32bit CRC of the file's data.
+        /// </summary>
         public uint CRC;
 
+        /// <summary>
+        /// The number of bytes contained in the index file.
+        /// </summary>
         public ushort PreloadBytes;
 
+        /// <summary>
+        /// A zero based index of the archive this file's data is contained in.
+        /// If 0x7fff, the data follows the directory.
+        /// </summary>
         public ushort ArchiveIndex;
 
+        /// <summary>
+        /// If ArchiveIndex is 0x7fff, the offset of the file data relative to the
+        /// end of the directory (see the header for more details).
+        /// Otherwise, the offset of the data from the start of the specified archive.
+        /// </summary>
         public uint EntryOffset;
 
+        /// <summary>
+        /// If zero, the entire file is stored in the preload data.
+        /// Otherwise, the number of bytes stored starting at EntryOffset.
+        /// </summary>
         public uint EntryLength;
 
         /// <summary>
diff --git a/SabreTools.Models/VPK/DirectoryItem.cs b/SabreTools.Models/VPK/DirectoryItem.cs
index 3d12235..6e6d824 100644
--- a/SabreTools.Models/VPK/DirectoryItem.cs
+++ b/SabreTools.Models/VPK/DirectoryItem.cs
@@ -1,6 +1,7 @@
 namespace SabreTools.Models.VPK
 {
     /// <see href="https://github.com/RavuAlHemio/hllib/blob/master/HLLib/VPKFile.h"/>
+    /// <see href="https://developer.valvesoftware.com/wiki/VPK_(file_format)"/>
     public sealed class DirectoryItem
     {
         public string? Extension { get; set; }
diff --git a/SabreTools.Models/VPK/ExtendedHeader.cs b/SabreTools.Models/VPK/ExtendedHeader.cs
index f4f8e58..e62a8cf 100644
--- a/SabreTools.Models/VPK/ExtendedHeader.cs
+++ b/SabreTools.Models/VPK/ExtendedHeader.cs
@@ -6,27 +6,33 @@ namespace SabreTools.Models.VPK
     /// Added in version 2.
     /// </summary>
     /// <see href="https://github.com/RavuAlHemio/hllib/blob/master/HLLib/VPKFile.h"/>
+    /// <see href="https://developer.valvesoftware.com/wiki/VPK_(file_format)"/>
     [StructLayout(LayoutKind.Sequential)]
     public sealed class ExtendedHeader
     {
         /// <summary>
-        /// Reserved
+        /// How many bytes of file content are stored in this
+        /// VPK file (0 in CSGO)
         /// </summary>
-        public uint Dummy0;
+        public uint FileDataSectionSize;
 
         /// <summary>
-        /// Archive hash length
+        /// The size, in bytes, of the section containing MD5
+        /// checksums for external archive content
         /// </summary>
-        public uint ArchiveHashLength;
+        public uint ArchiveMD5SectionSize;
 
         /// <summary>
-        /// Looks like some more MD5 hashes.
+        /// The size, in bytes, of the section containing MD5
+        /// checksums for content in this file (should always be 48)
         /// </summary>
-        public uint ExtraLength;
+        public uint OtherMD5SectionSize;
 
         /// <summary>
-        /// Reserved
+        /// The size, in bytes, of the section containing the public
+        /// key and signature. This is either 0 (CSGO & The Ship) or
+        /// 296 (HL2, HL2:DM, HL2:EP1, HL2:EP2, HL2:LC, TF2, DOD:S & CS:S)
         /// </summary>
-        public uint Dummy1;
+        public uint SignatureSectionSize;
     }
 }
diff --git a/SabreTools.Models/VPK/Header.cs b/SabreTools.Models/VPK/Header.cs
index ccaa7ff..aa57e1c 100644
--- a/SabreTools.Models/VPK/Header.cs
+++ b/SabreTools.Models/VPK/Header.cs
@@ -3,6 +3,7 @@ using System.Runtime.InteropServices;
 namespace SabreTools.Models.VPK
 {
     /// <see href="https://github.com/RavuAlHemio/hllib/blob/master/HLLib/VPKFile.h"/>
+    /// <see href="https://developer.valvesoftware.com/wiki/VPK_(file_format)"/>
     [StructLayout(LayoutKind.Sequential)]
     public sealed class Header
     {
@@ -13,6 +14,9 @@ namespace SabreTools.Models.VPK
 
         public uint Version;
 
-        public uint DirectoryLength;
+        /// <summary>
+        /// The size, in bytes, of the directory tree
+        /// </summary>
+        public uint TreeSize;
     }
 }
diff --git a/SabreTools.Models/VPK/OtherMD5Section.cs b/SabreTools.Models/VPK/OtherMD5Section.cs
new file mode 100644
index 0000000..976e6c3
--- /dev/null
+++ b/SabreTools.Models/VPK/OtherMD5Section.cs
@@ -0,0 +1,18 @@
+using System.Runtime.InteropServices;
+
+namespace SabreTools.Models.VPK
+{
+    /// <see href="https://developer.valvesoftware.com/wiki/VPK_(file_format)"/>
+    [StructLayout(LayoutKind.Sequential)]
+    public sealed class OtherMD5Section
+    {
+        [MarshalAs(UnmanagedType.ByValArray, SizeConst = 16)]
+        public byte[]? TreeChecksum = new byte[16];
+
+        [MarshalAs(UnmanagedType.ByValArray, SizeConst = 16)]
+        public byte[]? ArchiveMD5SectionChecksum = new byte[16];
+
+        [MarshalAs(UnmanagedType.ByValArray, SizeConst = 16)]
+        public byte[]? WholeFileChecksum = new byte[16];
+    }
+}
\ No newline at end of file
diff --git a/SabreTools.Models/VPK/SignatureSection.cs b/SabreTools.Models/VPK/SignatureSection.cs
new file mode 100644
index 0000000..1e1ae22
--- /dev/null
+++ b/SabreTools.Models/VPK/SignatureSection.cs
@@ -0,0 +1,29 @@
+using System.Runtime.InteropServices;
+
+namespace SabreTools.Models.VPK
+{
+    /// <see href="https://developer.valvesoftware.com/wiki/VPK_(file_format)"/>
+    [StructLayout(LayoutKind.Sequential)]
+    public sealed class SignatureSection
+    {
+        /// <summary>
+        /// Always seen as 160 (0xA0) bytes
+        /// </summary>
+        public uint PublicKeySize;
+
+        /// <summary>
+        /// <see cref="PublicKeySize"/> 
+        /// </summary>
+        public byte[]? PublicKey;
+
+        /// <summary>
+        /// Always seen as 128 (0x80) bytes
+        /// </summary>
+        public uint SignatureSize;
+
+        /// <summary>
+        /// <see cref="SignatureSize"/> 
+        /// </summary>
+        public byte[]? Signature;
+    }
+}
\ No newline at end of file