Biblio

Cloud storage brokerage systems abstract cloud storage complexities by mediating technical and business relationships between cloud stakeholders, while providing value-added services. This however raises security challenges pertaining to the integration of disparate components with sometimes conflicting security policies and architectural complexities. Assessing the security risks of these challenges is therefore important for Cloud Storage Brokers (CSBs). In this paper, we present a threat modeling schema to analyze and identify threats and risks in cloud brokerage brokerage systems. Our threat modeling schema works by generating attack trees, attack graphs, and data flow diagrams that represent the interconnections between identified security risks. Our proof-of-concept implementation employs the Common Configuration Scoring System (CCSS) to support the threat modeling schema, since current schemes lack sufficient security metrics which are imperatives for comprehensive risk assessments. We demonstrate the efficiency of our proposal by devising CCSS base scores for two attacks commonly launched against cloud storage systems: Cloud sStorage Enumeration Attack and Cloud Storage Exploitation Attack. These metrics are then combined with CVSS based metrics to assign probabilities in an Attack Tree. Thus, we show the possibility combining CVSS and CCSS for comprehensive threat modeling, and also show that our schemas can be used to improve cloud security.

In cloud storage systems, users can upload their data along with associated tags (authentication information) to cloud storage servers. To ensure the availability and integrity of the outsourced data, provable data possession (PDP) schemes convince verifiers (users or third parties) that the outsourced data stored in the cloud storage server is correct and unchanged. Recently, several PDP schemes with designated verifier (DV-PDP) were proposed to provide the flexibility of arbitrary designated verifier. A designated verifier (private verifier) is trustable and designated by a user to check the integrity of the outsourced data. However, these DV-PDP schemes are either inefficient or insecure under some circumstances. In this paper, we propose the first non-repudiable PDP scheme with designated verifier (DV-NRPDP) to address the non-repudiation issue and resolve possible disputations between users and cloud storage servers. We define the system model, framework and adversary model of DV-NRPDP schemes. Afterward, a concrete DV-NRPDP scheme is presented. Based on the computing discrete logarithm assumption, we formally prove that the proposed DV-NRPDP scheme is secure against several forgery attacks in the random oracle model. Comparisons with the previously proposed schemes are given to demonstrate the advantages of our scheme.