Securing synch & share data-at-rest


1003163361_ba156d12f7Snowden at SXSW said last week that it’s up to the vendors to encrypt customer data. I think he was talking mostly about data-in-flight but there’s just a big an exposure for data-at-rest, maybe more so because then, all the data is available, at one sitting.

iMessage security

A couple of weeks ago there was a TechCrunch article (see Apple Explains Exactly How Secure iMessage Really Is or see the Apple IOS Security document) about Apple’s iMessage security.

The documents said that Apple iMessage uses public key encryption where every IOS/OS X device generates a pair of public and private keys (one for messages and one for signing) which are used to encrypt the data while it is transmitted through Apple’s iMessage service.  Apple encrypts the data on its iMessage App running in the devices with every destination device’s public key before it’s saved on the iMessage server cloud, which can then be decrypted on the device with its private key whenever the message is received by the device.

It’s a bit more complex for longer messages and attachments but the gist is that this data is encrypted with a random key at the device and is saved in encrypted form while residing iMessage servers. This random key and URI is then encrypted with the destination devices public keys which is then stored on the iMessage servers. Once the destination device retrieves the message with an attachment it has the location and the random key to decrypt the attachment.

According to Apple’s documentation when you start an iMessage you identify the recipient, the app retrieves the public keys for all these devices and then it encrypts the message (with each destination device’s public message key) and signs the message (with the originating device’s private signing key). This way Apple servers never see the plain text message and never holds the decryption keys.

Synch & share data security today

As mentioned in prior posts, I am now a Dropbox user and utilize this service to synch various IOS and OSX device file data. Which means a copy of all this synch data is sitting on Dropbox (AWS S3) servers, someplace (possibly multiple places) in the cloud.

Dropbox data-at-rest security is explained in their How secure is Dropbox document. Essentially they use SSL for data-in-flight security and AES-256 encryption with a random key for data-at-rest security.

This probably makes it easier to support multiple devices and perhaps data sharing because they only need to encrypt/save the data once and can decrypt the data on its servers before sending it through (SSL encrypted, of course) to other devices.

The only problem is that Dropbox holds all the encryption keys for all the data that sits on its servers. I (and possibly the rest of the tech community) would much prefer that the data be encrypted at the customer’s devices and never decrypted again except at other customer devices. This would be true end-to-end data security for sync&share

As far as I know from a data-at-rest security perspective Box looks about the same, so does EMC’s Syncplicity, Oxygen Cloud, and probably all the others. There are some subtle differences about how and where the keys are kept and how many security domains exist in each service, but in the end, the service holds the keys to all data that is encrypted on their storage cloud.

Public key cryptography to the rescue

I think we could do better and public key cryptography should show us the way. I suppose it would probably be easiest to follow the iMessage approach and just encrypt all the data with each device’s public key at the time you create/update the data and send it to the service but,

  • That would further delay the transfer of new and updated data to the synch service, also further delaying its availability at other devices linked to the login.
  • That would cause the storage requirement for your sync&share data to be multiplied by the number of devices you wish to synch with.

Synch data-at-rest security

If we just take on the synch side of the discussion first maybe it would be easiest. For example,  if a new public and private key pair for encryption and signing were to be assigned to each new device at login to the service then the service could retain a directory of the device’s public keys for data encryption and signing.

The first device to login to a synch service with a new user-id, would assign a single encryption key for all data to be shared by all devices that could use this login.  As other devices log into the service, the prime device sends the single service encryption key encrypted using the target device’s public key and signing the message with the source device’s private key. Actually any device in the service ring could do this but the primary device could be used to authenticate the new devices login credentials. Each device’s synch service would have a list of all the public keys for all the devices in the “synch” region.

As data is created or updated there are two segments of each file that are created, the AES-256 encrypted data package using the “synch” region’s random encryption key and the signature package, signed by the device doing the creation/update of the file.  Any device could authenticate the signature package at the time it receives a file, as could the service. But ONLY the devices with the AES-256 encryption key would have access to the plain text version of the data.

There are some potential holes in this process, first is that the service could still intercept the random encryption key, at the primary device when it’s created or could retrieve it anytime later at its leisure using the app running in the device. This same exposure exists for the iMessage App running in IOS/OS X devices, the private keys in this instance could be sent to another party at any time. We would need to depend on service guarantees to not do this.

Share data-at-rest security

For Apple’s iMessage attachment security the data is kept in the cloud encrypted by a random key but the key and the URI are sent to the devices when they receive the original message. I suppose this could just as easily work for a file share service but the sharing activity might require a share service app running in the target device to create public-private key pairs and access the file.

Yes this leaves any “shared” data keys being held by the service but it can’t be helped. The data is being shared with others so maybe having it be a little more accessible to prying eyes would be acceptable.


I still prefer the iMessage approach, having multiple copies of encrypted shared data, that is encrypted by each device’s public key. It’s simpler this way, a bit more verifiable and doesn’t need to have as much out-of-channel communication (to send keys to other devices).

Yes it would cost more to store any amount of data and would take longer to transmit, but I feel we would all would be willing to support this extra constraints as long as the service guaranteed that private keys were only kept on devices that have logged into the service.

Data-at-rest and -in-flight security is becoming more important these days. Especially since Snowden’s exposure of what’s happening to web data. I love the great convenience of sync&share services, I just wish that the encryption keys weren’t so vulnerable…


Photo Credits: Prizon Planet by AZRainman

Enterprise file synch

Strange Clouds by michaelroper (cc) (from Flickr)
Strange Clouds by michaelroper (cc) (from Flickr)

Last fall at SNW in San Jose there were a few vendors touting enterprise file synchronization services each having a slightly different version of the requirements.   The one that comes most readily to mind was Egnyte which supported file synchronization across a hybrid cloud (public cloud and network storage) which we discussed in our Fall SNWUSA wrap up post last year.

The problem with BYOD

With bring your own devices (BYOD) corporate end users are quickly abandoning any pretense of IT control and turning consumer class file synchronization services to help  synch files across desktop, laptop and all mobile devices they haul around.   But the problem with these solutions such as DropBoxBoxOxygenCloud and others are that they are really outside of IT’s control.

Which is why there’s a real need today for enterprise class file synchronization solutions that exhibit the ease of use and set up available from consumer file synch systems but  offer IT security, compliance and control over the data that’s being moved into the cloud and across corporate and end user devices.

EMC Syncplicity and EMC on premises storage

Last week EMC announced an enterprise version of their recently acquired Syncplicity software that supports on-premises Isilon or Atmos storage, EMC’s own cloud storage offering.

In previous versions of Syncplicity storage was based in the cloud and used Amazon Web Services (AWS) for cloud orchestration and AWS S3 for cloud storage. With the latest release, EMC adds on premises storage to host user file synchronization services that can span mobile devices, laptops and end user desktops.

New Syncplicity users must download desktop client software to support file synchronization or mobile apps for mobile device synchronization.  After that it’s a simple matter of identifying which if any directories and/or files are to be synchronized with the cloud and/or shared with others.

However, with the Business (read enterprise) edition one also gets the Security and Compliance console which supports access control to define users and devices that can synchronize or share data, enforce data retention policies, remote wipe corporate data,  and native support for single sign services. In addition, one also gets centralized user and group management services to grant, change, revoke user and group access to data.  Also, one now obtains enterprise security with AES-256 data-at-rest encryption, separate key manager data centers and data storage data centers, quadruple replication of data for high disaster fault tolerance and SAS70 Type II compliant data centers.

If the client wants to use on premises storage, they would also need to deploy a VM virtual appliance somewhere in the data center to act as the gateway to file synchronization service requests. The file synch server would also presumably need access to the on premises storage and it’s unclear if the virtual appliance is in-band or out-of-band (see discussion on Egnyte’s solution options below).

Egnyte’s solution

Egnyte comes as a software only solution building a file server in the cloud for end user  storage. It also includes an Egnyte app for mobile hardware and the ever present web file browser.  Desktop file access is provided via mapped drives which access the Egnyte cloud file server gateway running as a virtual appliance.

One major difference between Syncplicity and Egnyte is that Egnyte offers a combination of both cloud and on premises storage but you cannot have just on premises storage. Syncplicity only offers one or the other storage for file data, i.e., file synchronization data can only be in the cloud or on local on premises storage but cannot be in both locations.

The other major difference is that Egnyte operates with just about anybody’s NAS storage such as EMC, IBM, and HDS for the on premises file storage.  It operates as an in-band, software appliance solution that traps file activity going to your on premises storage. In this case, one would need to start using a new location or directory for data to be synchronized or shared.

But for NetApp storage only (today), they utilize ONTAP APIs to offer out-of-band file synchronization solutions.  This means that you can keep NetApp data where it resides and just enable synchronization/shareability services for the NetApp file data in current directory locations.

Egnyte promises enterprise class data security with AD, LDAP and/or SSO user authentication, AES-256 data encryption and their own secure data centers.  No mention of separate key security in their literature.

As for cloud backend storage, Egnyte has it’s own public cloud or supports other cloud storage providers such as AWS S3, Microsoft Azure, NetApp Storage Grid and HP Public Cloud.

There’s more to Egnyte’s solution than just file synchronization and sharing but that’s the subject of today’s post. Perhaps we can cover them at more length in a future post if their interest.

File synchronization, cloud storage’s killer app?

The nice thing about these capabilities is that now IT staff can re-gain control over what is and isn’t synched and shared across multiple devices.  Up until now all this was happening outside the data center and external to IT control.

From Egnyte’s perspective, they are seeing more and more enterprises wanting data both on premises for performance and compliance as well as in the cloud storage for ubiquitous access.  They feel its both a sharability demand between an enterprise’s far flung team members and potentially client/customer personnel as well as a need to access, edit and propagate silo’d corporate information using new mobile devices that everyone has these days.

In any event, Enterprise file synchronization and sharing is emerging as one of the killer apps for cloud storage.  Up to this point cloud gateways made sense for SME backup or disaster recovery solutions but IMO, didn’t really take off beyond that space.  But if you can package a robust and secure file sharing and synchronization solution around cloud storage then you just might have something that enterprise customers are clamoring for.