Need to Calculate SHA1 hash of file stored in Azure storage in c#

Question

I am uploading large files (1-10 GB) to azure storage and need to calculate SHA1 hash value of files when uploaded. Am I able to calculate the SHA1 on the server, without having to download the file?

Answer 1

Azure Blob Storage support the MD5 hash calculation for blob automatically when putting blob, please see the content below of Get Blob Properties.

Content-MD5

If the Content-MD5 header has been set for the blob, this response header is returned so that the client can check for message content integrity. In version 2012-02-12 and newer, Put Blob sets a block blob’s MD5 value even when the Put Blob request doesn’t include an MD5 header.

So it's not necessary to calculate SHA1 hash for a blob if not has special needs.

As reference, here is a sample which calculate SHA1 hash without downloading for a blob stored in storage.

Synchronous

CloudStorageAccount storageAccount = CloudStorageAccount.Parse("<StorageAccountConnectionString>");
CloudBlobClient     blobClient     = storageAccount.CreateCloudBlobClient();
CloudBlobContainer  container      = blobClient.GetContainerReference("<container-name>");
CloudBlob           blob           = container.GetBlobReference("<blob-name>");

using(Stream blobStream = blob.OpenRead())
{
    using (SHA1 sha1 = SHA1.Create())
    {
        byte[] checksum = sha1.ComputeHash(blobStream);
    }
}

Async:

CloudStorageAccount storageAccount = CloudStorageAccount.Parse("<StorageAccountConnectionString>");
CloudBlobClient     blobClient     = storageAccount.CreateCloudBlobClient();
CloudBlobContainer  container      = blobClient.GetContainerReference("<container-name>");
CloudBlob           blob           = container.GetBlobReference("<blob-name>");

using(Stream blobStream = await blob.OpenReadAsync().ConfigureAwait(false))
{
    using (SHA1 sha1 = SHA1.Create())
    {
        byte[] checksum = await sha1.ComputeHashAsync(blobStream);
    }
}

// ComputeHashAsync extension method from https://www.tabsoverspaces.com/233439-computehashasync-for-sha1
public static async Task<Byte[]> ComputeHashAsync(this HashAlgorithm algo, Stream stream, Int32 bufferSize = 4096)
{
    algo.Initialize();

    var buffer = new byte[bufferSize];
    var streamLength = inputStream.Length;
    while (true)
    {
        var read = await inputStream.ReadAsync(buffer, 0, buffer.Length).ConfigureAwait(false);
        if (inputStream.Position == streamLength)
        {
            algo.TransformFinalBlock(buffer, 0, read);
            break;
        }
        algo.TransformBlock(buffer, 0, read, default(byte[]), default(int));
    }

    return algo.Hash;
}