A target-centric approach to cloud security

The XDet system associates a single block of data with a file and creates reference points within that block as a signature.

One of the main strengths of cloud storage – accessibility from anywhere and by any type of device – is also a major vulnerability. While firewalls and intrusion-detection systems provide some protection, they don’t help in cases where legitimate users’ devices or logins have been compromised.

That weakness explains how of celebrity photos – many containing nudity – that had been stored in Apple’s iCloud were downloaded in August 2014.  The data was apparently compromised by the hackers getting access to legitimate users’ login information.

In principle, files can be protected by controlling access with signatures – such as file hashes and JPEG header metadata.  Yet while those measures can provide assurance at the end points, there’s no way to check signatures within the network environment.

Two British computer scientists, however – Rob Hegarty of Manchester Metropolitan University and John Haggerty of Nottingham Trent University – have developed a system called XDet that associates a single block of data with a file and creates reference points within that block as a signature.

Compared to other signature schemes, said Hegarty, “one of the benefits of XDet is that we are only reading a single block from the files, so signature generation only takes a minute amount of time.”

Once the block signature is created, XDet monitors the HTTP/TCP data streams to look for the signed blocks.  Hegarty and his colleague acknowledge in their article – “Extrusion detection of illegal files in cloud-based systems” – that the reassembling of files does impose some overhead, which they are working to mitigate.

“What we detect is either the block leaving the network, or in the case of indecent images of children, the block being uploaded and entering the network,” said Hegarty.  When a mismatch is detected, the connection to the server will either be terminated immediately or the mismatch will simply be logged for later action, depending on how XDet is configured.

Hegarty emphasized that XDet is not a replacement for other security measures.  “The main difference between this and existing countermeasures such as firewalls and intrusion-detection systems is that we’re going for a target-centric approach,” he said.  “We care about the data being transferred.  We don’t care about the means.”

Hegarty said he and his colleague are looking to enhance XDet in several ways, including extending it to sign other kinds of files in addition to images.  And while the current system is configured to provide access control, he said it could easily be configured for file auditing if it was linked to a logging program.

According to Hegarty, XDet has already attracted interest from law enforcement agencies.

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