Cheap and Secure Cloud Backups

I’ve wanted to find a good provider of cheap and secure cloud backups for a while. I’ve compared some cloud drive providers, but didn’t quite like those. They usually have very limited free plans, somewhat pricey paid plans (e.g. 50GB for about 24$ a year for OneDrive), or like in the case of Google no information available at all. By the way, “Google one is coming soon” isn’t an announcement that I want to look at for more than a few days when looking for pricing info.

Then, I’ve looked at pricing of cloud storage providers, such as AWS, Azure and Google Cloud. Those offer storage around 1 cent ($0.01) per GB per month. That’s a quarter of the OneDrive cost! It’s even less if you consider their archive offerings (AWS Glacier, Archive in Azure, Coldline Storage for Google). The cheapest offering here is from Microsoft at 0.2 cents ($0.002) per GB per month, but with some usage caveats. Since the point of backups is to keep them for a long time, this quickly adds up though.

Now I’ve written a line or two of code before, so I figured I could as well write my own tool for this. So here is bart, the backup and restore tool. Note that at this point I do not offer bart as a ready-to-use executable, but only as MIT-licensed source code. In addition, bart currently works only with Azure Blob Storage – or with storage mounted into the machine’s file system. However, adding other cloud providers/archive destinations should be relatively easy, given the interfaces used in the tool.


In terms of security, bart encrypts every file before storing it in the archive destination. A user-provided password is used together with a randomly generated salt to derive a key for encryption with AES. On first use of any archive destination, bart generates a random salt, and each archive has its own password and salt. To avoid anybody with access to the archive destination from even snooping the names of your files, the names are hashed (SHA1) and the hashes used to store the encrypted files. This has the disadvantage that renaming/moving a file results in another file in the destination archive, though.


Once you compiled bart, you can use it as follows.

./bart [-name string] [-path string] [-m noop|restore|delete] -acct string -key string
  -name string
        The name of the backup archive. (default "backup")
  -path string
        The path to the directory to backup and/or restore. (default ".")
  -m string
        A behavior for files missing locally: 'noop' to do nothing, 'restore' to restore them from the backup, 'delete' to delete them in the backup archive. (default "noop")
  -acct string
        The Azure Storage Account name.
  -key string
        The Azure Storage Account Key.


The sources are on GitHub @


I’ve used bart for backup of some photos/videos for a while now. For the about 42GB I have uploaded so far my monthly bill from Microsoft is about 42 cents ($0.42). Those months where I upload new files the cost is a little higher (a few cents usually) because of the extra transactions. My backed up files are encrypted. If this isn’t cheap and secure cloud backups, what is?

Fighting Spam

I have updated my mail server code to report some very basic diagnostics data through performance counters (I’ll come back to that in a future post). Amongst the information that’s being logged are:

  • The total number of connections since the server was started.
  • The total number of connections refused (due to server and anti-spam policies) since the server was started.

I’ve looked at these numbers after a couple of hours of the server being online. There were about 60K connections, out of which a bit more than 75% have been refused SMTP transactions because the remote hosts were identified as spam senders.


Finding the Private Key File of Certificates

At work, I have created multiple tools which we used to analyse and fix issues related to certificates that we use with Office Communications Server and their respective private key files. To summarize, a user/service who wants to use the certificate for authentication needs to have read access on the private key. If it doesn’t, you’ll typically see a strange error which many people don’t relate to missing ACLs on the private key file.

Now these days, you don’t need to write such tools anymore. PowerShell allows you to pretty much do everything you need in this area. Let’s look at the following PS script (let’s call it FindPrivateKey.ps1) which accepts a parameter of type System.Security.Cryptography.X509Certificates.X509Certificate2, i.e. a reference to the certificate you want to analyze.


echo "Looking for private key file of certificate"
echo $Certificate
echo ""
echo "The private key file is '$($Certificate.PrivateKey.CspKeyContainerInfo.UniqueKeyContainerName)'"
echo ""

$file = ls $env:userprofile -Filter $Certificate.PrivateKey.CspKeyContainerInfo.UniqueKeyContainerName -Recurse -Force -EA SilentlyContinue
echo "It is located at '$($file.FullName)'."

I guess I do not need to mention that you can easily find the certificate you’re interested in by running something like

pushd cert:\CurrentUser\My
$cert = gci 0DAC31905AEB722D8561BFAF3F3BFD2F551AA197
.\FindPrivateKey.ps1 $cert

where ‘0DAC31905AEB722D8561BFAF3F3BFD2F551AA197’ is simply the thumbprint of the certificate we’re interested in. From here on it should be easy to check what ACLs the file has (run $file.GetAccessControl()) and to modify them (run $file.SetAccessControl()).