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Hello, 

 After updating existing password-protected zip archives using ZipFile.Add() or ZipFile.Delete() methods they become unusable by #ziplib.

Version of I used is "0.85.4.369"

1) I added the following test routine to the SharpZipLib.Tests.Zip.GeneralHandling (took PartialStreamClosing() as a base)

        /// <summary>
        /// Added by Serg 5/8/2008
        /// </summary>
        [Test]
        [Category("Zip")]
        [Category("CreatesTempFile")]
        public void UpdateArchive()
        {
            string tempFile = GetTempFilePath();
            Assert.IsNotNull(tempFile, "No permission to execute this test?");

            if (tempFile != null)
            {
                tempFile = Path.Combine(tempFile, "SharpZipTest.Zip");
                MakeZipFile(tempFile, new String[ { "Farriera", "Champagne", "Urban myth" }, 10, "Aha", "123456");

                using (ZipFile zipFile = new ZipFile(tempFile))
                {
                    zipFile.Password = "123456";
                    Assert.IsTrue(zipFile.TestArchive(true));

                    zipFile.BeginUpdate();
                    zipFile.Delete("Farriera");
                    zipFile.CommitUpdate();
                    Assert.IsTrue(zipFile.TestArchive(true));

                    zipFile.Close();
                }
                File.Delete(tempFile);
            }
        }

 2) I added modified routine for archive creation to SharpZipLib.Tests.Zip.ZipBase (sets password and does not use zip64)

        /// <summary>
        /// Added by Serg 5/8/2008
        /// </summary>
        protected void MakeZipFile(string name, string[ names, int size, string comment, string password)
        {
            using (FileStream fs = File.Create(name))
            {
                using (ZipOutputStream zOut = new ZipOutputStream(fs))
                {
                    zOut.UseZip64 = UseZip64.Off;
                    zOut.Password = password;
                    zOut.SetComment(comment);
                    for (int i = 0; i < names.Length; ++i)
                    {
                        zOut.PutNextEntry(new ZipEntry(names[i]));
                        AddKnownDataToEntry(zOut, size);
                    }
                    zOut.Close();
                }
                fs.Close();
            }
        }

The test I added fails. If password is set to an empty string (in the test above it's "123456"), test passes.

"Dirty" fix I found is in SharpZipLib.Zip.ZipFile.GetDescriptorSize() function.

This is existing code, fails:

        int GetDescriptorSize(ZipUpdate update)
        {
            int result = 0;
            if ( (update.Entry.Flags & (int)GeneralBitFlags.Descriptor) != 0) {
                result = ZipConstants.DataDescriptorSize - 4;
                if ( update.Entry.LocalHeaderRequiresZip64 ) {
                    result = ZipConstants.Zip64DataDescriptorSize - 4;
                }
            }
            return result;
        }

This is modified code, works:

        int GetDescriptorSize(ZipUpdate update)
        {
            int result = 0;
            if ( (update.Entry.Flags & (int)GeneralBitFlags.Descriptor) != 0) {
                result = ZipConstants.DataDescriptorSize - 0;
                if ( update.Entry.LocalHeaderRequiresZip64 ) {
                    result = ZipConstants.Zip64DataDescriptorSize - 4;
                }
            }
            return result;
        }

 Fixing descriptor size seems to help.

 I hope the issue makes sense and is clear enough.

I don't have zip format specification to see whether the change I did is legit and that code itself is not explaining

(don't see why data descriptor size is reduced by 4 bytes)

Thanks for attention and best regards,

Serg