//zip.cs
using System;
using System.Collections.Generic;
using System.Text;
using System.IO;
using System.IO.Compression;
 
namespace GZipStreamC
{
    public class ZipStream
    {        
        public static string Zip(string text)
        {
            byte[] buffer = Encoding.UTF8.GetBytes(text);
            MemoryStream ms = new MemoryStream();
            using (GZipStream zip = new GZipStream(ms, CompressionMode.Compress, true))
            {
                zip.Write(buffer, 0, buffer.Length);
            }
            ms.Position = 0;
            byte[] compressed = new byte[ms.Length];
            ms.Read(compressed, 0, compressed.Length);
            byte[] gzBuffer = new byte[compressed.Length + 4];
            System.Buffer.BlockCopy(compressed, 0, gzBuffer, 4, compressed.Length);
            System.Buffer.BlockCopy(BitConverter.GetBytes(buffer.Length), 0, gzBuffer, 0, 4);
            return Convert.ToBase64String(gzBuffer);
        }
        public static string UnZip(string compressedText)
        {
            byte[] gzBuffer = Convert.FromBase64String(compressedText);
            using (MemoryStream ms = new MemoryStream())
            {
                int msgLength = BitConverter.ToInt32(gzBuffer, 0);
                ms.Write(gzBuffer, 4, gzBuffer.Length - 4);
                byte[] buffer = new byte[msgLength];
                ms.Position = 0;
                using (GZipStream zip = new GZipStream(ms, CompressionMode.Decompress))
                {
                    zip.Read(buffer, 0, buffer.Length);
                }
                return Encoding.UTF8.GetString(buffer);
            }
        }
    }
}

csc /target:library /out:zip.DLL zip.cs

Imports GZipStreamC.ZipStream
Public Class Form1
 
    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        TextBox1.Text = Zip(TextBox1.Text)
    End Sub
 
    Private Sub Button2_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button2.Click
        TextBox1.Text = UnZip(TextBox1.Text)
    End Sub
End Class