AES encrypted input stream throws exception on close

Hi All!

Recently we decided to use AES encrypted zip files in our app and I have found a problem with this lib, it throws NotImplementedException when calling Dispose method on input stream for encrypted entry after reading is done.

Sample code to reproduce problem:

    public void CloseStreamTest()
        {
            var _zipFile = new ZipFile(@"encrypted.zip") { Password = @"123456789" };
            //File.txt is AES-256 encrypted file
            var entryIdx = _zipFile.FindEntry(@"File.txt", true);
            if (entryIdx >= 0)
            {
                var zipped = _zipFile.GetInputStream(entryIdx);
                //We're able to get all data
                ReadStream(original, zipped);
                //Next statement throws NotImplementedException
                zipped.Close();
            }
        }

I have created a patch for this. Changes include 2 files:

•   Encryption\ZipAESTransform.cs

source lines 167-170
        public byte[ TransformFinalBlock(byte[ inputBuffer, int inputOffset, int inputCount) {

            throw new NotImplementedException("ZipAESTransform.TransformFinalBlock");
        }
to (changed)
        public byte[ TransformFinalBlock(byte[ inputBuffer, int inputOffset, int inputCount)
        {
            byte[ result;
            if (!_finalised)
            {
                result = new byte[inputCount];
                TransformBlock(inputBuffer, inputOffset, inputCount, result, 0);
            }
            else
            {
                result = new byte[0];
            }
            return result;
        }

•   Encryption\ZipAESStream.cs

source lines 132-166
_transform.TransformBlock(_slideBuffer,
                          _slideBufStartPos,
                          finalBlock,
                          outBuffer,
                          offset);
to (changed)
var fb = _transform.TransformFinalBlock(_slideBuffer,
                                        _slideBufStartPos,
                                        finalBlock);
Array.Copy(fb, 0, outBuffer, offset, fb.Length);



I will be glad to see this changes in SharpZipLib.

Best Regards