Crisis.Ionic.Zip.ZipEntry.GetLengthOfCryptoHeaderBytes C# (CSharp) Method

        internal static int GetLengthOfCryptoHeaderBytes(EncryptionAlgorithm a)
        {
            //if ((_BitField & 0x01) != 0x01) return 0;
            if (a == EncryptionAlgorithm.None) return 0;

#if AESCRYPTO
            if (a == EncryptionAlgorithm.WinZipAes128 ||
                a == EncryptionAlgorithm.WinZipAes256)
            {
                int KeyStrengthInBits = GetKeyStrengthInBits(a);
                int sizeOfSaltAndPv = ((KeyStrengthInBits / 8 / 2) + 2);
                return sizeOfSaltAndPv;
            }
#endif
            if (a == EncryptionAlgorithm.PkzipWeak)
                return 12;
            throw new ZipException("internal error");
        }

        /// <summary>
        ///   Reads one entry from the zip directory structure in the zip file.
        /// </summary>
        ///
        /// <param name="zf">
        ///   The zipfile for which a directory entry will be read.  From this param, the
        ///   method gets the ReadStream and the expected text encoding
        ///   (ProvisionalAlternateEncoding) which is used if the entry is not marked
        ///   UTF-8.
        /// </param>
        ///
        /// <param name="previouslySeen">
        ///   a list of previously seen entry names; used to prevent duplicates.
        /// </param>
        ///
        /// <returns>the entry read from the archive.</returns>
        internal static ZipEntry ReadDirEntry(ZipFile zf,
                                              Dictionary <String, Object> previouslySeen)
        {
            System.IO.Stream     s = zf.ReadStream;
            System.Text.Encoding expectedEncoding = (zf.AlternateEncodingUsage == ZipOption.Always)
                ? zf.AlternateEncoding
                : ZipFile.DefaultEncoding;

            int signature = Crisis.Ionic.Zip.SharedUtilities.ReadSignature(s);

            // return null if this is not a local file header signature
            if (IsNotValidZipDirEntrySig(signature))
            {
                s.Seek(-4, System.IO.SeekOrigin.Current);
                // workitem 10178
                Crisis.Ionic.Zip.SharedUtilities.Workaround_Ladybug318918(s);

                // Getting "not a ZipDirEntry signature" here is not always wrong or an
                // error.  This can happen when walking through a zipfile.  After the
                // last ZipDirEntry, we expect to read an
                // EndOfCentralDirectorySignature.  When we get this is how we know
                // we've reached the end of the central directory.
                if (signature != ZipConstants.EndOfCentralDirectorySignature &&
                    signature != ZipConstants.Zip64EndOfCentralDirectoryRecordSignature &&
                    signature != ZipConstants.ZipEntrySignature  // workitem 8299
                    )
                {
                    throw new BadReadException(String.Format("  Bad signature (0x{0:X8}) at position 0x{1:X8}", signature, s.Position));
                }
                return(null);
            }

            int bytesRead = 42 + 4;

            byte[] block = new byte[42];
            int    n     = s.Read(block, 0, block.Length);

            if (n != block.Length)
            {
                return(null);
            }

            int      i   = 0;
            ZipEntry zde = new ZipEntry();

            zde.AlternateEncoding = expectedEncoding;
            zde._Source           = ZipEntrySource.ZipFile;
            zde._container        = new ZipContainer(zf);

            unchecked
            {
                zde._VersionMadeBy     = (short)(block[i++] + block[i++] * 256);
                zde._VersionNeeded     = (short)(block[i++] + block[i++] * 256);
                zde._BitField          = (short)(block[i++] + block[i++] * 256);
                zde._CompressionMethod = (Int16)(block[i++] + block[i++] * 256);
                zde._TimeBlob          = block[i++] + block[i++] * 256 + block[i++] * 256 * 256 + block[i++] * 256 * 256 * 256;
                zde._LastModified      = Crisis.Ionic.Zip.SharedUtilities.PackedToDateTime(zde._TimeBlob);
                zde._timestamp        |= ZipEntryTimestamp.DOS;

                zde._Crc32            = block[i++] + block[i++] * 256 + block[i++] * 256 * 256 + block[i++] * 256 * 256 * 256;
                zde._CompressedSize   = (uint)(block[i++] + block[i++] * 256 + block[i++] * 256 * 256 + block[i++] * 256 * 256 * 256);
                zde._UncompressedSize = (uint)(block[i++] + block[i++] * 256 + block[i++] * 256 * 256 + block[i++] * 256 * 256 * 256);
            }

            // preserve
            zde._CompressionMethod_FromZipFile = zde._CompressionMethod;

            zde._filenameLength   = (short)(block[i++] + block[i++] * 256);
            zde._extraFieldLength = (short)(block[i++] + block[i++] * 256);
            zde._commentLength    = (short)(block[i++] + block[i++] * 256);
            zde._diskNumber       = (UInt32)(block[i++] + block[i++] * 256);

            zde._InternalFileAttrs = (short)(block[i++] + block[i++] * 256);
            zde._ExternalFileAttrs = block[i++] + block[i++] * 256 + block[i++] * 256 * 256 + block[i++] * 256 * 256 * 256;

            zde._RelativeOffsetOfLocalHeader = (uint)(block[i++] + block[i++] * 256 + block[i++] * 256 * 256 + block[i++] * 256 * 256 * 256);

            // workitem 7801
            zde.IsText = ((zde._InternalFileAttrs & 0x01) == 0x01);

            block      = new byte[zde._filenameLength];
            n          = s.Read(block, 0, block.Length);
            bytesRead += n;
            if ((zde._BitField & 0x0800) == 0x0800)
            {
                // UTF-8 is in use
                zde._FileNameInArchive = Crisis.Ionic.Zip.SharedUtilities.Utf8StringFromBuffer(block);
            }
            else
            {
                zde._FileNameInArchive = Crisis.Ionic.Zip.SharedUtilities.StringFromBuffer(block, expectedEncoding);
            }

            // workitem 10330
            // insure unique entry names
            while (previouslySeen.ContainsKey(zde._FileNameInArchive))
            {
                zde._FileNameInArchive = CopyHelper.AppendCopyToFileName(zde._FileNameInArchive);
                zde._metadataChanged   = true;
            }

            if (zde.AttributesIndicateDirectory)
            {
                zde.MarkAsDirectory();  // may append a slash to filename if nec.
            }
            // workitem 6898
            else if (zde._FileNameInArchive.EndsWith("/"))
            {
                zde.MarkAsDirectory();
            }

            zde._CompressedFileDataSize = zde._CompressedSize;
            if ((zde._BitField & 0x01) == 0x01)
            {
                // this may change after processing the Extra field
                zde._Encryption_FromZipFile = zde._Encryption =
                    EncryptionAlgorithm.PkzipWeak;
                zde._sourceIsEncrypted = true;
            }

            if (zde._extraFieldLength > 0)
            {
                zde._InputUsesZip64 = (zde._CompressedSize == 0xFFFFFFFF ||
                                       zde._UncompressedSize == 0xFFFFFFFF ||
                                       zde._RelativeOffsetOfLocalHeader == 0xFFFFFFFF);

                // Console.WriteLine("  Input uses Z64?:      {0}", zde._InputUsesZip64);

                bytesRead += zde.ProcessExtraField(s, zde._extraFieldLength);
                zde._CompressedFileDataSize = zde._CompressedSize;
            }

            // we've processed the extra field, so we know the encryption method is set now.
            if (zde._Encryption == EncryptionAlgorithm.PkzipWeak)
            {
                // the "encryption header" of 12 bytes precedes the file data
                zde._CompressedFileDataSize -= 12;
            }
#if AESCRYPTO
            else if (zde.Encryption == EncryptionAlgorithm.WinZipAes128 ||
                     zde.Encryption == EncryptionAlgorithm.WinZipAes256)
            {
                zde._CompressedFileDataSize = zde.CompressedSize -
                                              (ZipEntry.GetLengthOfCryptoHeaderBytes(zde.Encryption) + 10);
                zde._LengthOfTrailer = 10;
            }
#endif

            // tally the trailing descriptor
            if ((zde._BitField & 0x0008) == 0x0008)
            {
                // sig, CRC, Comp and Uncomp sizes
                if (zde._InputUsesZip64)
                {
                    zde._LengthOfTrailer += 24;
                }
                else
                {
                    zde._LengthOfTrailer += 16;
                }
            }

            // workitem 12744
            zde.AlternateEncoding = ((zde._BitField & 0x0800) == 0x0800)
                ? System.Text.Encoding.UTF8
                :expectedEncoding;

            zde.AlternateEncodingUsage = ZipOption.Always;

            if (zde._commentLength > 0)
            {
                block      = new byte[zde._commentLength];
                n          = s.Read(block, 0, block.Length);
                bytesRead += n;
                if ((zde._BitField & 0x0800) == 0x0800)
                {
                    // UTF-8 is in use
                    zde._Comment = Crisis.Ionic.Zip.SharedUtilities.Utf8StringFromBuffer(block);
                }
                else
                {
                    zde._Comment = Crisis.Ionic.Zip.SharedUtilities.StringFromBuffer(block, expectedEncoding);
                }
            }
            //zde._LengthOfDirEntry = bytesRead;
            return(zde);
        }