Add support for AES encrypted zip entries whose size is determined by a data descriptor rather than a local file header.

Author: Remo Gloor

src/ICSharpCode.SharpZipLib/Encryption/ZipAESTransform.cs

@@ -51,6 +51,7 @@ static class HashAlgorithmName
 		private byte[] _authCode = null;
 
 		private bool _writeMode;
+		private Action<int> _appendHmac = remaining => { };
 
 		/// <summary>
 		/// Constructor.
@@ -88,6 +89,23 @@ public ZipAESTransform(string key, byte[] saltBytes, int blockSize, bool writeMo
 			_writeMode = writeMode;
 		}
 
+		/// <summary>
+		/// Append all of the last transformed input data to the HMAC.
+		/// </summary>
+		public void AppendAllPending()
+		{
+			_appendHmac(0);
+		}
+		
+		/// <summary>
+		/// Append all except the number of bytes specified by remaining of the last transformed input data to the HMAC.
+		/// </summary>
+		/// <param name="remaining">The number of bytes not to be added to the HMAC. The excluded bytes are form the end.</param>
+		public void AppendFinal(int remaining)
+		{
+			_appendHmac(remaining);
+		}		
+
 		/// <summary>
 		/// Implement the ICryptoTransform method.
 		/// </summary>
@@ -97,8 +115,16 @@ public int TransformBlock(byte[] inputBuffer, int inputOffset, int inputCount, b
 			// This does not change the inputBuffer. Do this before decryption for read mode.
 			if (!_writeMode)
 			{
-				_hmacsha1.AppendData(inputBuffer, inputOffset, inputCount);
+				if (!ManualHmac)
+				{
+					_hmacsha1.AppendData(inputBuffer, inputOffset, inputCount);
+				}
+				else
+				{
+					_appendHmac = remaining => _hmacsha1.AppendData(inputBuffer, inputOffset, inputCount - remaining);
+				}
 			}
+
 			// Encrypt with AES in CTR mode. Regards to Dr Brian Gladman for this.
 			int ix = 0;
 			while (ix < inputCount)
@@ -208,6 +234,13 @@ public bool CanReuseTransform
 			}
 		}
 
+		/// <summary>
+		/// Gets of sets a value indicating if the HMAC is updates on every read of if updating the HMAC has to be controlled manually
+		/// Manual control of HMAC is needed in case not all the Transformed data should be automatically added to the HMAC.
+		/// E.g. because its not know how much data belongs to the current entry before the data is decrypted and analyzed. 
+		/// </summary>
+		public bool ManualHmac { get; set; }
+
 		/// <summary>
 		/// Cleanup internal state.
 		/// </summary>

src/ICSharpCode.SharpZipLib/Zip/Compression/Streams/InflaterInputStream.cs

@@ -1,6 +1,7 @@
 using System;
 using System.IO;
 using System.Security.Cryptography;
+using ICSharpCode.SharpZipLib.Encryption;
 
 namespace ICSharpCode.SharpZipLib.Zip.Compression.Streams
 {
@@ -92,7 +93,15 @@ public byte[] ClearText
 		public int Available
 		{
 			get { return available; }
-			set { available = value; }
+			set
+			{
+				if (cryptoTransform is ZipAESTransform ct)
+				{
+					ct.AppendFinal(value);
+				}
+				
+				available = value;
+			}
 		}
 
 		/// <summary>
@@ -121,6 +130,11 @@ public void SetInflaterInput(Inflater inflater)
 		/// </summary>
 		public void Fill()
 		{
+			if (cryptoTransform is ZipAESTransform ct)
+			{
+				ct.AppendAllPending();
+			}
+
 			rawLength = 0;
 			int toRead = rawData.Length;
 
@@ -313,6 +327,11 @@ private int CalculateDecryptionSize(int availableBufferSize)
 		{
 			int size = DecryptionLimit ?? availableBufferSize;
 			size = Math.Min(size, availableBufferSize);
+			if (size < 0)
+			{
+				size = availableBufferSize;
+			}
+			
 			if (DecryptionLimit.HasValue)
 			{
 				DecryptionLimit -= size;

src/ICSharpCode.SharpZipLib/Zip/ZipInputStream.cs

@@ -618,6 +618,7 @@ private int InitialRead(byte[] destination, int offset, int count)
 					int blockSize = entry.AESKeySize / 8;   // bits to bytes
 
 					var decryptor = new ZipAESTransform(password, saltBytes, blockSize, false);
+					decryptor.ManualHmac = csize < 0;
 					byte[] pwdVerifyCalc = decryptor.PwdVerifier;
 					if (pwdVerifyCalc[0] != pwdVerifyRead[0] || pwdVerifyCalc[1] != pwdVerifyRead[1])
 					{

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

@@ -15,7 +15,7 @@ static ZipEncryptionHandling()
 			var sb = new StringBuilder();
 			for (int i = 0; i < 1000; i++)
 			{
-				sb.Append(Guid.NewGuid());
+				sb.AppendLine(Guid.NewGuid().ToString());
 			}
 
 			DummyDataString = sb.ToString();
@@ -126,17 +126,23 @@ public void ZipFileAesDecryption()
 		[Test]
 		[Category("Encryption")]
 		[Category("Zip")]
-		[TestCase(0, CompressionMethod.Deflated)]
-		[TestCase(0, CompressionMethod.Stored)]
-		[TestCase(128, CompressionMethod.Deflated)]
-		[TestCase(128, CompressionMethod.Stored)]
-		[TestCase(256, CompressionMethod.Deflated)]
-		[TestCase(256, CompressionMethod.Stored)]
-		public void ZipInputStreamDecryption(int aesKeySize, CompressionMethod compressionMethod)
+		[TestCase(0, CompressionMethod.Deflated, false)]
+		[TestCase(0, CompressionMethod.Stored, false)]
+		[TestCase(128, CompressionMethod.Deflated, false)]
+		[TestCase(128, CompressionMethod.Stored, false)]
+		[TestCase(256, CompressionMethod.Deflated, false)]
+		[TestCase(256, CompressionMethod.Stored, false)]
+		[TestCase(0, CompressionMethod.Deflated, true)]
+		[TestCase(0, CompressionMethod.Stored, true)]
+		[TestCase(128, CompressionMethod.Deflated, true)]
+		[TestCase(128, CompressionMethod.Stored, true)]
+		[TestCase(256, CompressionMethod.Deflated, true)]
+		[TestCase(256, CompressionMethod.Stored, true)]
+		public void ZipInputStreamDecryption(int aesKeySize, CompressionMethod compressionMethod, bool forceDataDescriptor)
 		{
 			var password = "password";
 
-			using (var ms = new MemoryStream())
+			using (var ms = forceDataDescriptor ? new NonSeekableMemoryStream() : new MemoryStream())
 			{
 				WriteEncryptedZipToStream(ms, 3, password, aesKeySize, compressionMethod);
 				ms.Seek(0, SeekOrigin.Begin);
@@ -544,6 +550,17 @@ public void CreateZipWithEncryptedEntries(string password, int keySize, Compress
 			}
 		}
 
+		private class NonSeekableMemoryStream : MemoryStream
+		{
+			public override bool CanSeek
+			{
+				get
+				{
+					return false;
+				}
+			}
+		}
+
 		private static readonly string DummyDataString;
 	}
 }