About Encryption

29 12 2014

Would you like to be able to use QR-Codes in order to let people quickly get some sensitive information, but also want to be able to restrict the number of people with access to the data? And what about iWork documents containing personal data? Is there a way to securely manage them?

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If you use an app like Qrafter by Kerem Erkan you may have the idea to use password-protected QR-Codes for sending sensitive data e.g. via mail or a messaging app like iMessage.

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The idea seems to be fascinating but let’s face the facts with an answer of the developer Kerem I got via E-Mail:

The encryption is 48-bit, meaning it is weak for any sensitive information. More secure encryption methods take too much data and QR Codes do not have such capacity. You should not use QR Code encryption for anything sensitive.

For the sake of security, it’s hard to beat the old-school, in-person hand off. It’s not the most sexy of options in the digital age, but surely there’s something titillating about a top-secret document hand off. Bring your briefcase and make it like a spy movie. Or don’t.

Don’t send your sensitive documents over email. It may seem private, but even if you’re using an email account that uploads attachments over a more secure HTTPS connection, like GMail, you have no control over your recipient’s server, and they may download your attachment from an unencrypted HTTP connection. Now say they did that from a public Wi-Fi network. Things just got very un-secure.

Some basics …

If you want your data to be NSA-resistant all files must be encrypted on your device before being transferred to the cloud. Your password should never be stored on your device or, if it’s stored there should never leave it. So no unauthorized user, not even employees of your provider, could ever access your data. Client-side encryption is the keyword.

Since encryption occurs before files leave your device it effectively wraps a protective wall around your data in the cloud. Employees then have very limited access to your data. They can only see how many files you have stored and how much storage space they occupy. The files themselves, as well as all metadata (folder names, file names, comments, preview images, etc.), are encrypted. The following chart illustrates three typical encryption schemes. The scheme in the middle is what is used by most cloud storage providers.

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What matters most when encrypting data is not the particular encryption algorithm (e.g. AES), but how it is used. Basically, there are three encryption schemes:

  • 1 None
    No encryption is used. Your data is sent to the storage in plain view, visible to anyone who has access to your network connection as well as to the storage provider. This is a little bit like sending someone a postcard: everyone involved in handling the postcard can read it.
  • 2 Encrypted connection (e.g. SSL)
    In this scheme, a secure channel is established between your computer and the storage provider before data is uploaded. That way, no one can eavesdrop on the transfer. However, the provider sees all your data. Often storage providers implement additional measures like creating corporate policies that disallow their employees to view your data. Another additional measure is using encrypted disks to store your data, so someone breaking into the data center and stealing the hard drives won’t be able to read it. However, it is still visible to the provider and its employees. This approach has the advantage that the provider can process your data for you, such as for creating a search index. Also, it is technically easy to make the data available in the web browser or through an API. The problem with this approach is that your privacy is limited. The storage provider can, for example, be forced to provide your data to a government agency. What’s more, employees will be able to read your data even if prohibited by company policies. It is also much more likely that bugs or other errors could result in data leaks. This is the most widespread approach implemented by cloud storage providers.
  • 3 Client-side encryption
    This approach is inherently more secure than the others. Apart from Box and Wuala, there are only a few other cloud storage providers following this scheme, mostly backup services. All data is encrypted locally on your device before it is uploaded. No one not explicitly authorized by you can see your data. Since not even the storage provider can see your data, they cannot be forced to hand it over to government agencies. The employees are also not able to read your data. As a side effect, it is impossible to recover your password in case you forget it. You can test your cloud storage provider’s security by checking whether they offer password recovery or password reset. If yes, then it does not employ client-side encryption. With client-side encryption, security is embedded deeply in the design of the storage.

    One of the main challenges with client-side encryption is key management. If you only want to back up, a single master key is enough. However, if you want to be able to share data selectively, your cloud storage must feature a sophisticated key management scheme.

With this in mind here is a more secure method to store sensitive data permanently or to exchange information with others.

Use a secure cloud storage, e.g. WUALA or BOX or an encryption software like BOXCRYPTOR and send the information as an encrypted file, a simple text message, a PDF file, or an iWork document.

Say you and your tech-savvy recipient set up a shared folder. Anything you put in that folder would travel encrypted from your folder to the provider’s servers to your recipient’s folder. That’s it.

Boxcryptor …

You use a cloud storage with standard, that means no, additional sevcurity?
Don’t worry. There is a solution for all well-known clouds including all other clouds which support the WebDAV protocol. It’s an application developed by the German company Secomba GmbH.

This video explains how Boxcryptor works.


(2:36 min)

Boxcryptor creates a virtual drive on your device that allows you to encrypt your files locally before uploading them to your cloud or clouds of choice. It encrypts individual files – and does not create containers.

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Any file dropped into an encrypted folder within the Boxcryptor drive will get automatically encrypted before it is synced to the cloud. To protect your files, Boxcryptor uses the AES-256 and RSA encryption algorithms.

Boxcryptor is free for one device and one cloud provider. You cannot use two iOS devices to manage encrypted files as long as both devices are linked to Boxcryptor. If you want to share encrypted files with others you can do that without a subscription.

A workaround …

You cannot turn off iCloud for individual iWork documents. So, creating a new document with sensitive data is a risk because the content automatically finds its way into iCloud.
Even if you turn off iCloud for documents but still use iCloud for backing up your device, your documents will be stored in iCloud and Apple has the key to decrypt them.

Here is a workaround which lets you manage encrypted iWork documents using Boxcryptor.

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This is definitely not a comfortable way but the only option to keep sensitive information away from unauthorized people. Even if government comes knocking there is no chance to decrypt your data regardless of the provider keeping your files. I would understand if you say “I hear the message well but lack faith’s constant trust.”.

Summary …

Sad to say that effective encryption is still not a standard feature of using cloud storages. Even Apple doesn’t use client-side encryption and so you should be careful when creating documents with sensitive data. Even if you deactivate syncing via iCloud your documents will find their way into the cloud when your iPad or iPhone initiates the next backup to iCloud.

Related links …

About QR-Codes

Mystic signs of progress

About encryption

Notes on encryption

About clouds

The cloudy iCloud

Risky free clouds

iOS cloud clients

Box for iOS

Thanks for flying with iNotes4You.


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