Cloud Computing systems are complex systems that leverage different technologies and can be deployed in different ways such as public, private and hybrid, as well as provide services such as IaaS, PaaS, and SaaS. All this implies that it can be a challenge to understand how to make a cloud secure. We need to understand its security issues and how to make cloud environments secure. In this work, we have provided the following contributions:
1. We performed a systematic review of security issues for cloud environments where we enumerated the main cloud threats and vulnerabilities found in the literature [3]. In this analysis, we presented a categorization of security issues focused in each service model (SaaS, PaaS, and IaaS), and we identified which service model can be affected by these security issues. Also, we described the relationship between these threats and vulnerabilities and provided possible countermeasures for each identified threat identified.
2. We developed a reference architecture to have a precise view of cloud systems [150]. Since clouds are complex systems, we presented each service model in the form of patterns which describe their requirements, characteristics, main units, and the relationship between these units. We also included some use cases that describe common functions for cloud services in general as well as for each service model.
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3. We described three specific cloud threats in the form of misuse patterns: Resource Usage Monitoring Inference, Malicious Virtual Machine Creation, and Malicious Virtual Machine Migration. The Resource Usage Monitoring Inference misuse pattern describes how an attacker tries to co-locate his virtual machine in the same server as the victim in order to infer some information. The Malicious Virtual Machine Creation misuse pattern depicts how an attacker can create a virtual machine image which contains malicious code in order to infect other virtual machines that use this image. Malicious Virtual Machine Migration describes how a virtual machine can be compromised while being migrated.
4. We showed how to secure a reference architecture by applying security patterns to add security defenses and misuse patterns to evaluate its security level. Besides the systematic review of security issues mentioned in 1), we also followed an approach from [141] in order to find possible threats by analyzing the activities from each use case. We analyzed an activity diagram for use cases create and publish a virtual machine image in order to identify possible threats. Once identified the threats, we followed the approach in [149] in order to find a matching security pattern to defend against these threats.
5. We developed a pattern for a secure virtual machine repository system which offers a secure control of virtual machine images by removing or hiding unwanted information. Then, we evaluated the level of security by showing how this security stops or mitigates these threats.
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This work can be extended by completing the catalog of misuse patterns to include those threats identified in [3]. From Table 3, we can identify some threats that can be described as misuse patterns:
Covert channels in clouds – covert channels allow inter-VM communication bypassing the security rules of the hypervisor.
Virtual machine escape – describes how to exploit the hypervisor in order to take control of the underlying platform.
Virtual machine hopping – describes how a virtual machine can access other virtual machines by exploiting the hypervisor for example.
Sniffing virtual networks – describes how a virtual machine can listen to the virtual network traffic in order to get confidential information.
Spoofing virtual networks – describes how a malicious virtual machine can intercept information in the virtual network with the purpose of altering its routing function.
A good number of security patterns have been produced [151], but we still need to adjust them to be valid for cloud environments or to develop new security patterns that are specific for clouds. Also from Table 4, we can identify some security mechanism and represent them as security patterns:
Secure migration process – provides a continuous protection for live migration and offline migration as well.
Secure hypervisor – reinforces the security of the hypervisor to avoid some attacks.
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Secure virtual networks – secures the communication among virtual machines. Virtualized trusted platform module – provides a framework to determine whether
the environment is secure before launching a virtual machine.
Web applications scanners – scans web applications in order to identify security vulnerabilities.
Cloud data protection – protects sensitive data while it is processed, stored or transferred. (encryption, digital signature, fragmentation-redundancy-scattering, homomorphic encryption)
Developing a good catalog for both security and misuse patterns can help designers and architects to use the reference architecture in order to add security and evaluate its security.
Another use of this cloud architecture is to be a reference for security certification of services. A cloud provider can show that his services can handle the corresponding threats which can increase customer trust. Also, a reference architecture can be used to support standards. It helps architects or designers to identify what components of the cloud system are associated with the standard and can be used to comply with the specific rules of the standard.
Moreover, hybrid clouds are becoming more popular due to security and privacy issues associated to public clouds. This reference architecture also provides general information for organizations wishing to integrate their existing IT processes and system with cloud infrastructure. Before migrating any process or system, organizations should refer to the cloud architecture to plan a strategy for integrating existing resources to
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clouds, to understand the inherent issues and limitations, and to think in terms to moving some processes and data to the cloud.
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