Add AES encryption support to ZipFile

Author: Numpsy

src/ICSharpCode.SharpZipLib/Encryption/ZipAESEncryptionStream.cs

@@ -0,0 +1,140 @@
+using System;
+using System.IO;
+using System.Security.Cryptography;
+
+namespace ICSharpCode.SharpZipLib.Encryption
+{
+	/// <summary>
+	/// Encrypts AES ZIP entries.
+	/// </summary>
+	/// <remarks>
+	/// Based on information from http://www.winzip.com/aes_info.htm
+	/// and http://www.gladman.me.uk/cryptography_technology/fileencrypt/
+	/// </remarks>
+	internal class ZipAESEncryptionStream : Stream
+	{
+		// The transform to use for encryption.
+		private ZipAESTransform transform;
+
+		// The output stream to write the encrypted data to.
+		private readonly Stream outputStream;
+
+		// Static to help ensure that multiple files within a zip will get different random salt
+		private static readonly RandomNumberGenerator _aesRnd = RandomNumberGenerator.Create();
+
+		/// <summary>
+		/// Constructor
+		/// </summary>
+		/// <param name="stream">The stream on which to perform the cryptographic transformation.</param>
+		/// <param name="rawPassword">The password used to encrypt the entry.</param>
+		/// <param name="saltLength">The length of the salt to use.</param>
+		/// <param name="blockSize">The block size to use for transforming.</param>
+		public ZipAESEncryptionStream(Stream stream, string rawPassword, int saltLength, int blockSize)
+		{
+			// Set up stream.
+			this.outputStream = stream;
+
+			// Initialise the encryption transform.
+			var salt = new byte[saltLength];
+
+			// Salt needs to be cryptographically random, and unique per file
+			_aesRnd.GetBytes(salt);
+			
+			this.transform = new ZipAESTransform(rawPassword, salt, blockSize, true);
+
+			// File format for AES:
+			// Size (bytes)   Content
+			// ------------   -------
+			// Variable       Salt value
+			// 2              Password verification value
+			// Variable       Encrypted file data
+			// 10             Authentication code
+			//
+			// Value in the "compressed size" fields of the local file header and the central directory entry
+			// is the total size of all the items listed above. In other words, it is the total size of the
+			// salt value, password verification value, encrypted data, and authentication code.
+			var pwdVerifier = this.transform.PwdVerifier;
+			this.outputStream.Write(salt, 0, salt.Length);
+			this.outputStream.Write(pwdVerifier, 0, pwdVerifier.Length);
+		}
+
+		// This stream is write only.
+		public override bool CanRead => false;
+
+		// We only support writing - no seeking about.
+		public override bool CanSeek => false;
+
+		// Supports writing for encrypting.
+		public override bool CanWrite => true;
+
+		// We don't track this.
+		public override long Length => throw new NotImplementedException();
+
+		// We don't track this, or support seeking.
+		public override long Position { get => throw new NotImplementedException(); set => throw new NotImplementedException(); }
+
+		/// <summary>
+		/// When the stream is disposed, write the final blocks and AES Authentication code
+		/// </summary>
+		protected override void Dispose(bool disposing)
+		{
+			if (this.transform != null)
+			{
+				this.WriteAuthCode();
+				this.transform.Dispose();
+				this.transform = null;
+			}
+		}
+
+		// <inheritdoc/>
+		public override void Flush()
+		{
+			this.outputStream.Flush();
+		}
+
+		// <inheritdoc/>
+		public override int Read(byte[] buffer, int offset, int count)
+		{
+			// ZipAESEncryptionStream is only used for encryption.
+			throw new NotImplementedException();
+		}
+
+		// <inheritdoc/>
+		public override long Seek(long offset, SeekOrigin origin)
+		{
+			// We don't support seeking.
+			throw new NotImplementedException();
+		}
+
+		// <inheritdoc/>
+		public override void SetLength(long value)
+		{
+			// We don't support setting the length.
+			throw new NotImplementedException();
+		}
+
+		// <inheritdoc/>
+		public override void Write(byte[] buffer, int offset, int count)
+		{
+			if (count == 0)
+			{
+				return;
+			}
+
+			var outputBuffer = new byte[count];
+			var outputCount = this.transform.TransformBlock(buffer, offset, count, outputBuffer, 0);
+			this.outputStream.Write(outputBuffer, 0, outputCount);
+		}
+
+		// Write the auth code for the encrypted data to the output stream
+		private void WriteAuthCode()
+		{
+			// Transform the final block?
+
+			// Write the AES Authentication Code (a hash of the compressed and encrypted data)
+			var authCode = this.transform.GetAuthCode();
+			this.outputStream.Write(authCode, 0, 10);
+			this.outputStream.Flush();
+		}
+	}
+}

src/ICSharpCode.SharpZipLib/Zip/ZipFile.cs

@@ -1872,10 +1872,10 @@ public void Add(IStaticDataSource dataSource, ZipEntry entry)
 
 			// We don't currently support adding entries with AES encryption, so throw
 			// up front instead of failing or falling back to ZipCrypto later on
-			if (entry.AESKeySize > 0)
-			{
-				throw new NotSupportedException("Creation of AES encrypted entries is not supported");
-			}
+			//if (entry.AESKeySize > 0)
+			//{
+			//	throw new NotSupportedException("Creation of AES encrypted entries is not supported");
+			//}
 
 			CheckSupportedCompressionMethod(entry.CompressionMethod);
 			CheckUpdating();
@@ -2164,6 +2164,12 @@ private void WriteLocalEntryHeader(ZipUpdate update)
 				ed.Delete(1);
 			}
 
+			// Write AES Data if needed
+			if (entry.AESKeySize > 0)
+			{
+				AddExtraDataAES(entry, ed);
+			}
+
 			entry.ExtraData = ed.GetEntryData();
 
 			WriteLEShort(name.Length);
@@ -2287,6 +2293,11 @@ private int WriteCentralDirectoryHeader(ZipEntry entry)
 				ed.Delete(1);
 			}
 
+			if (entry.AESKeySize > 0)
+			{
+				AddExtraDataAES(entry, ed);
+			}
+
 			byte[] centralExtraData = ed.GetEntryData();
 
 			WriteLEShort(centralExtraData.Length);
@@ -2341,6 +2352,22 @@ private int WriteCentralDirectoryHeader(ZipEntry entry)
 			return ZipConstants.CentralHeaderBaseSize + name.Length + centralExtraData.Length + rawComment.Length;
 		}
 
+		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);
+		}
+
 		#endregion Writing Values/Headers
 
 		private void PostUpdateCleanup()
@@ -3714,9 +3741,16 @@ private Stream CreateAndInitDecryptionStream(Stream baseStream, ZipEntry entry)
 
 		private Stream CreateAndInitEncryptionStream(Stream baseStream, ZipEntry entry)
 		{
-			CryptoStream result = null;
-			if ((entry.Version < ZipConstants.VersionStrongEncryption)
-				|| (entry.Flags & (int)GeneralBitFlags.StrongEncryption) == 0)
+			if (entry.CompressionMethodForHeader == CompressionMethod.WinZipAES)
+			{
+				int blockSize = entry.AESKeySize / 8;   // bits to bytes
+
+				var aesStream =
+					new ZipAESEncryptionStream(baseStream, rawPassword_, entry.AESSaltLen, blockSize);
+
+				return aesStream;
+			}
+			else
 			{
 				var classicManaged = new PkzipClassicManaged();
 
@@ -3728,7 +3762,7 @@ private Stream CreateAndInitEncryptionStream(Stream baseStream, ZipEntry entry)
 
 				// Closing a CryptoStream will close the base stream as well so wrap it in an UncompressedStream
 				// which doesnt do this.
-				result = new CryptoStream(new UncompressedStream(baseStream),
+				CryptoStream result = new CryptoStream(new UncompressedStream(baseStream),
 					classicManaged.CreateEncryptor(key, null), CryptoStreamMode.Write);
 
 				if ((entry.Crc < 0) || (entry.Flags & 8) != 0)
@@ -3739,8 +3773,9 @@ private Stream CreateAndInitEncryptionStream(Stream baseStream, ZipEntry entry)
 				{
 					WriteEncryptionHeader(result, entry.Crc);
 				}
+
+				return result;
 			}
-			return result;
 		}
 
 		private static void CheckClassicPassword(CryptoStream classicCryptoStream, ZipEntry entry)

test/ICSharpCode.SharpZipLib.Tests/Zip/ZipFileHandling.cs

@@ -1552,6 +1552,7 @@ public void HostSystemPersistedFromZipFile()
 		/// Refs https://github.com/icsharpcode/SharpZipLib/issues/385
 		/// Trying to add an AES Encrypted entry to ZipFile should throw as it isn't supported
 		/// </summary>
+#if false
 		[Test]
 		[Category("Zip")]
 		public void AddingAnAESEncryptedEntryShouldThrow()
@@ -1569,6 +1570,7 @@ public void AddingAnAESEncryptedEntryShouldThrow()
 				Assert.That(exception.Message, Is.EqualTo("Creation of AES encrypted entries is not supported"));
 			}
 		}
+#endif
 
 		/// <summary>
 		/// Test that we can add a file entry and set the name to sometihng other than the name of the file.