Creating hash for folder

Question

i need to create hash for folder, that contains some files. I already done this task for each of files, but i searching the way to create one hash for all files in folder.

Answer 1

Here's a solution that uses streaming to avoid memory and latency issues.

By default the file paths are included in the hashing, which will factor not only the data in the files, but the file system entries themselves, which avoids hash collisions. This post is tagged security, so this ought to be important.

Finally, this solution puts you in control the hashing algorithm and which files get hashed and in what order.

public static class HashAlgorithmExtensions
{
    public static async Task ComputeHashAsync(this HashAlgorithm alg, IEnumerable files, bool includePaths = true)
    {
        using (var cs = new CryptoStream(Stream.Null, alg, CryptoStreamMode.Write))
        {
            foreach (var file in files)
            {
                if (includePaths)
                {
                    var pathBytes = Encoding.UTF8.GetBytes(file.FullName);
                    cs.Write(pathBytes, 0, pathBytes.Length);
                }

                using (var fs = file.OpenRead())
                    await fs.CopyToAsync(cs);
            }

            cs.FlushFinalBlock();
        }

        return alg.Hash;
    }
}

An example that hashes all the files in a folder:

async Task HashFolder(DirectoryInfo folder, string searchPattern = "*", SearchOption searchOption = SearchOption.TopDirectoryOnly)
{
    using(var alg = MD5.Create())
        return await alg.ComputeHashAsync(folder.EnumerateFiles(searchPattern, searchOption));
}