Security Against Key Recovery Attacks in Digital Rights Management Systems

Abstract

With the invention of high speed internet and content digitization, large scale content sharing became exceptionally easy. This ease added fuel to the fire of piracy, which caused a gigantic loss to content providers. Copyright laws only caused deterrence. Hence a technological solution was required to protect the rights of digital content owners. This inevitably gave birth to Digital Rights Management System (DRM). DRM could not fulfill the obligations and is broken from time to time. Each DRM system uses its own proprietary approach of implementation. Further, the DRM systems achieve security of sensitive information, like secret keys and algorithms, through obscurity. By and large each DRM system hides the sensitive information like content decryption keys at some place on end user’s device in encrypted form. But ultimately there has to be some key encrypting key which is required to be in plain, else there will not be any start point of decryption. Here lies the problem of recovering the unencrypted key stored at some secret place on end user’s device. Due to this problem, illegitimate decryption of contents becomes possible, thus leading to piracy. Two major types of attacks faced by DRM are the key recovery and unencrypted content capturing. In this thesis a DRM model has been proposed which will employ elliptic curve integrated encryption system (ECIES) and a secure one-way hash function for generating a dynamic one time content encryption/ decryption key. A portion of key is stored in license. With the proposed technique, the knowledge of a portion of key will reveal no information about the key itself. The key will never be reused and will never be stored persistently on end user device. The proposed solution will make key recovery and piracy, difficult. If any effort is made to distribute the contents illegally, the content will be locked cryptographically for both legal and illegal consumers. The proposed technique also provides protection against attacks, wherein an attacker becomes successful in extracting the content decryption key and publishes it on a public website database. With the help of some well-known techniques like remote attestation, the proposed technique also allows checking the integrity of DRM client software which is executed in malicious host environment. Unencrypted content capturing attacks are out of the scope of this thesis. Further the techniques like strong anti-debugging, Code flattening and code obfuscation will raise the scale of difficulty for dynamic analysis key recovery attacks.