Question

estoy usando la librería sharpLibZip para comprimir y descomprimir archivos en zip quisiera saber de que manera al momento de descomprimir podría validar si la contraseña es correcta o no , y en dado caso que sea incorrecta mande un mensaje.

CÓDIGO COMPRIMIR

public void CreateSample(string outPathname, string password, string folderName)
    {

        FileStream fsOut = File.Create(outPathname);
        ZipOutputStream zipStream = new ZipOutputStream(fsOut);

        zipStream.SetLevel(3); //0-9, 9 being the highest level of compression

        zipStream.Password = password;  // optional. Null is the same as not setting. Required if using AES.

        int folderOffset = folderName.Length + (folderName.EndsWith("\\") ? 0 : 1);

        CompressFolder(folderName, zipStream, folderOffset);

        zipStream.IsStreamOwner = true; // Makes the Close also Close the underlying stream
        zipStream.Close();
    }

    // Recurses down the folder structure
    //
    private void CompressFolder(string path, ZipOutputStream zipStream, int folderOffset)
    {

        string[] files = Directory.GetFiles(path);

        foreach (string filename in files)
        {

            FileInfo fi = new FileInfo(filename);

            string entryName = filename.Substring(folderOffset); // Makes the name in zip based on the folder
            entryName = ZipEntry.CleanName(entryName); // Removes drive from name and fixes slash direction
            ZipEntry newEntry = new ZipEntry(entryName);
            newEntry.DateTime = fi.LastWriteTime; // Note the zip format stores 2 second granularity

            // Specifying the AESKeySize triggers AES encryption. Allowable values are 0 (off), 128 or 256.
            // A password on the ZipOutputStream is required if using AES.
            //   newEntry.AESKeySize = 256;

            // To permit the zip to be unpacked by built-in extractor in WinXP and Server2003, WinZip 8, Java, and other older code,
            // you need to do one of the following: Specify UseZip64.Off, or set the Size.
            // If the file may be bigger than 4GB, or you do not need WinXP built-in compatibility, you do not need either,
            // but the zip will be in Zip64 format which not all utilities can understand.
            zipStream.UseZip64 = UseZip64.Off;
            newEntry.Size = fi.Length;

            zipStream.PutNextEntry(newEntry);

            // Zip the file in buffered chunks
            // the "using" will close the stream even if an exception occurs
            byte[] buffer = new byte[4096];
            using (FileStream streamReader = File.OpenRead(filename))
            {
                StreamUtils.Copy(streamReader, zipStream, buffer);
            }
            zipStream.CloseEntry();
        }
        string[] folders = Directory.GetDirectories(path);
        foreach (string folder in folders)
        {
            CompressFolder(folder, zipStream, folderOffset);
        }
    }
}
}

CODIGO DESCOMPRIMIR

public void ExtractZipFile(string archiveFilenameIn, string password, string outFolder)
    {
        ZipFile zf = null;
        try
        {
            FileStream fs = File.OpenRead(archiveFilenameIn);
            zf = new ZipFile(fs);
            if (!String.IsNullOrEmpty(password))
            {
                zf.Password = password;     // AES encrypted entries are handled automatically

            }
            foreach (ZipEntry zipEntry in zf)
            {
                if (!zipEntry.IsFile)
                {
                    continue;           // Ignore directories
                }
                String entryFileName = zipEntry.Name;
                // to remove the folder from the entry:- entryFileName = Path.GetFileName(entryFileName);
                // Optionally match entrynames against a selection list here to skip as desired.
                // The unpacked length is available in the zipEntry.Size property.

                byte[] buffer = new byte[4096];     // 4K is optimum

               // Stream zipStream = zf.GetInputStream(zipEntry);
                Stream zipStream = zf.GetInputStream(zipEntry);
                // Manipulate the output filename here as desired.
                String fullZipToPath = Path.Combine(outFolder, entryFileName);
                string directoryName = Path.GetDirectoryName(fullZipToPath);
                if (directoryName.Length > 0)
                    Directory.CreateDirectory(directoryName);

                // Unzip file in buffered chunks. This is just as fast as unpacking to a buffer the full size
                // of the file, but does not waste memory.
                // The "using" will close the stream even if an exception occurs.
                using (FileStream streamWriter = File.Create(fullZipToPath))
                {
                    StreamUtils.Copy(zipStream, streamWriter, buffer);
                }
            }
        }
        finally
        {
            if (zf != null)
            {
                zf.IsStreamOwner = true; // Makes close also shut the underlying stream
                zf.Close(); // Ensure we release resources
            }
        }
    }

saludos.

Answer 1

Nunca he usado sharpLibZip y por lo tanto no conozco sus funcionalidades ni si tiene alguna función que permita esta comprobación (Sí que existe por ejemplo IsCrypted para comprobar si es necesaria la contraseña pero no sé si existe alguna para comprobar la validez de la misma).

¿Qué sucede si se intenta descomprimir con contraseña errónea? Si devuelve una excepción y no encuentras otra solución una posible chapucilla puede ser implementar un try catch que compruebe si la descompresión ha dado errores.