Experiment with using ITaggedData for AES extra data handling

src/ICSharpCode.SharpZipLib/Zip/ZipEntry.cs

@@ -1129,26 +1129,21 @@ private DateTime GetDateTime(ZipExtraData extraData)
 		//
 		private void ProcessAESExtraData(ZipExtraData extraData)
 		{
-			if (extraData.Find(0x9901))
+			var aesData = extraData.GetData<WinZipAESTaggedData>();
+
+			if (aesData != null)
 			{
 				// Set version for Zipfile.CreateAndInitDecryptionStream
 				versionToExtract = ZipConstants.VERSION_AES;            // Ver 5.1 = AES see "Version" getter
 
-				//
-				// Unpack AES extra data field see http://www.winzip.com/aes_info.htm
-				int length = extraData.ValueLength;         // Data size currently 7
-				if (length < 7)
-					throw new ZipException("AES Extra Data Length " + length + " invalid.");
-				int ver = extraData.ReadShort();            // Version number (1=AE-1 2=AE-2)
-				int vendorId = extraData.ReadShort();       // 2-character vendor ID 0x4541 = "AE"
-				int encrStrength = extraData.ReadByte();    // encryption strength 1 = 128 2 = 192 3 = 256
-				int actualCompress = extraData.ReadShort(); // The actual compression method used to compress the file
-				_aesVer = ver;
-				_aesEncryptionStrength = encrStrength;
-				method = (CompressionMethod)actualCompress;
+				_aesVer = (int)aesData.Version;
+				_aesEncryptionStrength = aesData.EncryptionStrength;
+				method = aesData.CompressionMethod;
 			}
 			else
+			{
 				throw new ZipException("AES Extra Data missing");
+			}
 		}
 
 		/// <summary>

src/ICSharpCode.SharpZipLib/Zip/ZipExtraData.cs

@@ -14,7 +14,7 @@ public interface ITaggedData
 		/// <summary>
 		/// Get the ID for this tagged data value.
 		/// </summary>
-		short TagID { get; }
+		ushort TagID { get; }
 
 		/// <summary>
 		/// Set the contents of this instance from the data passed.
@@ -40,7 +40,7 @@ public class RawTaggedData : ITaggedData
 		/// Initialise a new instance.
 		/// </summary>
 		/// <param name="tag">The tag ID.</param>
-		public RawTaggedData(short tag)
+		public RawTaggedData(ushort tag)
 		{
 			_tag = tag;
 		}
@@ -50,7 +50,7 @@ public RawTaggedData(short tag)
 		/// <summary>
 		/// Get the ID for this tagged data value.
 		/// </summary>
-		public short TagID
+		public ushort TagID
 		{
 			get { return _tag; }
 			set { _tag = value; }
@@ -99,7 +99,7 @@ public byte[] Data
 		/// <summary>
 		/// The tag ID for this instance.
 		/// </summary>
-		private short _tag;
+		private ushort _tag;
 
 		private byte[] _data;
 
@@ -138,7 +138,7 @@ public enum Flags : byte
 		/// <summary>
 		/// Get the ID
 		/// </summary>
-		public short TagID
+		public ushort TagID
 		{
 			get { return 0x5455; }
 		}
@@ -327,7 +327,7 @@ public class NTTaggedData : ITaggedData
 		/// <summary>
 		/// Get the ID for this tagged data value.
 		/// </summary>
-		public short TagID
+		public ushort TagID
 		{
 			get { return 10; }
 		}
@@ -474,6 +474,110 @@ public DateTime LastAccessTime
 		#endregion Instance Fields
 	}
 
+	/// <summary>
+	/// A TaggedData for handling WinzipAES extra data.
+	/// </summary>
+	/// <remarks>
+	/// See http://www.winzip.com/aes_info.htm for format documentation.
+	/// </remarks>
+	internal class WinZipAESTaggedData : ITaggedData
+	{
+		/// <summary>
+		/// The Version used by this entry.
+		/// </summary>
+		/// <remarks>
+		/// AE-1 iS 1. AE-2 is 2. With AE-2 no CRC is required and 0 is stored.
+		/// </remarks>
+		public enum VendorVersion : int
+		{
+			/// <summary>
+			/// Version AE-1.
+			/// </summary>
+			AE1 = 0x0001,
+
+			/// <summary>
+			/// Version AE-2.
+			/// </summary>
+			AE2 = 0x0002,
+		}
+
+		/// <summary>
+		/// Get the ID for this tagged data value.
+		/// </summary>
+		public ushort TagID => 0x9901;
+
+		/// <summary>
+		/// Set the data from the raw values provided.
+		/// </summary>
+		/// <param name="data">The raw data to extract values from.</param>
+		/// <param name="index">The index to start extracting values from.</param>
+		/// <param name="count">The number of bytes available.</param>
+		public void SetData(byte[] data, int index, int count)
+		{
+			using (MemoryStream ms = new MemoryStream(data, index, count, false))
+			using (ZipHelperStream helperStream = new ZipHelperStream(ms))
+			{
+				//
+				// Unpack AES extra data field see http://www.winzip.com/aes_info.htm
+				var length = helperStream.Length;         // Data size currently 7
+				if (length < 7)
+					throw new ZipException("AES Extra Data Length " + length + " invalid.");
+
+				int ver = helperStream.ReadLEShort();            // Version number (1=AE-1 2=AE-2)
+				int vendorId = helperStream.ReadLEShort();       // 2-character vendor ID 0x4541 = "AE"
+				int encrStrength = helperStream.ReadByte();    // encryption strength 1 = 128 2 = 192 3 = 256
+				int actualCompress = helperStream.ReadLEShort(); // The actual compression method used to compress the file
+
+				this.Version = (VendorVersion)ver;
+				this.EncryptionStrength = (byte)encrStrength;
+				this.CompressionMethod = (CompressionMethod)actualCompress;
+			}
+		}
+
+		/// <summary>
+		/// Get the binary data representing this instance.
+		/// </summary>
+		/// <returns>The raw binary data representing this instance.</returns>
+		public byte[] GetData()
+		{
+			using (MemoryStream ms = new MemoryStream())
+			using (ZipHelperStream helperStream = new ZipHelperStream(ms))
+			{
+				helperStream.IsStreamOwner = false;
+
+				// Vendor ID is the two ASCII characters "AE".
+				const int VENDOR_ID = 0x4541; //not 6965;
+
+				// Pack AES extra data field see http://www.winzip.com/aes_info.htm
+				// extraData.AddLeShort(7);                              // Data size (currently 7)
+				helperStream.WriteLEShort((int)this.Version);            // Entry version
+				helperStream.WriteLEShort(VENDOR_ID);                    // "AE"
+				helperStream.WriteByte(this.EncryptionStrength);         // 1 = 128, 2 = 192, 3 = 256
+				helperStream.WriteLEShort((int)this.CompressionMethod);  // The actual compression method used to compress the file
+
+				return ms.ToArray();
+			}
+		}
+
+		/// <summary>
+		/// Get/set the <see cref="VendorVersion"> for this entry.</see>
+		/// </summary>
+		/// <remarks>
+		/// Defaults to 2 because we always use that when encrypting new entries.
+		/// </remarks>
+		public VendorVersion Version { get; set; } = VendorVersion.AE2;
+
+		/// <summary>
+		/// Get /set the real <see cref="CompressionMethod"> for this entry.</see>.
+		/// </summary>
+		public CompressionMethod CompressionMethod { get; set; }
+
+		/// <summary>
+		/// Get /set the encryption strength for this entry - 1 = 128 bit, 2 = 192 bit, 3 = 256 bit
+		/// </summary>	
+		public byte EncryptionStrength { get; set; }
+	}
+
 	/// <summary>
 	/// A factory that creates <see cref="ITaggedData">tagged data</see> instances.
 	/// </summary>

src/ICSharpCode.SharpZipLib/Zip/ZipOutputStream.cs

@@ -609,18 +609,13 @@ private void WriteEncryptionHeader(long crcValue)
 
 		private static void AddExtraDataAES(ZipEntry entry, ZipExtraData extraData)
 		{
-			// Vendor Version: AE-1 IS 1. AE-2 is 2. With AE-2 no CRC is required and 0 is stored.
-			const int VENDOR_VERSION = 2;
-			// Vendor ID is the two ASCII characters "AE".
-			const int VENDOR_ID = 0x4541; //not 6965;
-			extraData.StartNewEntry();
-			// Pack AES extra data field see http://www.winzip.com/aes_info.htm
-			//extraData.AddLeShort(7);							// Data size (currently 7)
-			extraData.AddLeShort(VENDOR_VERSION);               // 2 = AE-2
-			extraData.AddLeShort(VENDOR_ID);                    // "AE"
-			extraData.AddData(entry.AESEncryptionStrength);     //  1 = 128, 2 = 192, 3 = 256
-			extraData.AddLeShort((int)entry.CompressionMethod); // The actual compression method used to compress the file
-			extraData.AddNewEntry(0x9901);
+			var aesData = new WinZipAESTaggedData
+			{
+				CompressionMethod = entry.CompressionMethod,
+				EncryptionStrength = entry.AESEncryptionStrength,
+			};
+
+			extraData.AddEntry(aesData);
 		}
 
 		// Replaces WriteEncryptionHeader for AES