ZipUtil.cs

using System.Collections.Generic;
using System.IO;
using System.IO.Compression;

public static class ZipUtil
{
    public static byte[] Compress(this Dictionary<string, byte[]> entries)
    {
        using (var stream = new MemoryStream())
        {
            using (var archive = new ZipArchive(stream, ZipArchiveMode.Create))
            {
                foreach (var entry in entries)
                {
                    var e = archive.CreateEntry(entry.Key);

                    using (var s = e.Open())
                    {
                        s.Write(entry.Value, 0, entry.Value.Length);
                    }
                }
            }

            return stream.ToArray();
        }
    }

    public static Dictionary<string, byte[]> Decompress(this byte[] buffer)
    {
        var ret = new Dictionary<string, byte[]>();

        using (var stream = new MemoryStream(buffer))
        using (var archive = new ZipArchive(stream, ZipArchiveMode.Read))
        {
            foreach (var entry in archive.Entries)
            {
                var name = entry.FullName;
                var data = new byte[entry.Length];

                using (var s = entry.Open())
                {
                    for (var count = 0; count < data.Length;)
                    {
                        count += s.Read(data, count, data.Length - count);
                    }
                }

                ret.Add(name, data);
            }
        }

        return ret;
    }
}