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Cloud File Storage and Collaboration: Core Security Features

By Rich

This is part 3 of our Security Pro’s Guide to Cloud File Storage and Collaboration (file sync and share). The full paper is available on GitHub as we write it. See also part 1 and part 2 here.

Identity and Access Management

Managing users and access are the most important features after the security baseline. The entire security and governance model relies on it. These are the key elements to look for:

  • Service and federated IDM: The cloud service needs to implement an internal identity model to allow sharing with external parties without requiring those individuals or organizations to register with your internal identity provider. The service also must support federated identity so you can use your internal directory and don’t need to manually register all your users with the service. SAML is the preferred standard. Both models should support API access, which is key to integrating the service with your applications as back-end storage.
  • Authorization and access controls: Once you establish and integrate identity the service should support a robust and granular permissions model. The basics include user and group access at the directory, subdirectory, and file levels. The model should integrate internal, external, and anonymous users. Permissions should include read, write/edit, download, and view (web viewing but not downloading of files). Additional permissions manage who can share files (internally and externally), alter permissions, comment, or delete files.

External Users

An external authenticated user is one who registers with the cloud provider but isn’t part of your organization. This is important for collaborative group shares, such as deal and project rooms. Most services also support public external shares, but these are open to the world. That is why providers need to support both their own platform user model and federated identity to integrate with your existing internal directory.

  • Device control: Cloud storage services are very frequently used to support mobile users on a variety of devices. Device control allows management of which devices (computers and mobile devices) are authorized for which users, to ensure only authorized devices have access.
  • Two-factor authentication (2FA): Account credential compromise is a major concern, so some providers can require a second authentication factor to access their services. Today this is typically a text message with a one-time password sent to a registered mobile phone. The second factor is generally only required to access the service from a ‘new’ (unregistered) device or computer.
  • Centralized management: Administrators can manage all permissions and sharing through the service’s web interface. For enterprise deployments this includes enterprise-wide policies, such as restricting external sharing completely and auto-expiring all shared links after a configurable interval. Administrators should also be able to identify all shared links without having to crawl through the directory structure.

Sharing permissions and policies are a key differentiator between enterprise-class and consumer services. For enterprises central control and management of shares is essential. So is the ability to manage who can share content externally, with what permissions, and to which categories of users (e.g., restricted to registered users vs. via an open file link). You might, for example, only allow employees to share with authenticated users on an enterprise-wide basis. Or only allow certain user roles to share files externally, and even then only with in-browser viewing only, with links set to expire in 30 days.

Each organizations has its own tolerances for sharing and file permissions. Granular controls allow you to align your use of the service with existing policies. These can also be a security benefit, providing centralized control over all storage, unlike the traditional model where you need to manage dozens or even thousands of different systems, with different authentication methods, and authorization models, and permissions.

Audit and transparency

One of the most powerful security features of cloud storage services is a complete audit log of all user and device activity. Enterprise-class services track all activity: which users touch which files from which devices. Features to look for include:

  • Completeness of the audit log: It should include user, device, accessed file, what activity was performed (download/view/edit, with before and after versions if appropriate), and additional metadata such as location.
  • Log duration: How much data does the audit log contain? Is it eternal or does it expire in 90 days?
  • Log management and visibility: How do you access the log? Is the user interface navigable and centralized, or do you need to hunt around and click individual files? Can you filter and report by user, file, and device?
  • Integration and export: Logs should be externally consumable in a standard format to integrate with existing log management and SIEM tools. Administrators should also be able to export activity reports and raw logs.

These features don’t cover everything offered by these services, but they are the core security capabilities enterprise and business users should have to start with.

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