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Cloud Data Security: Archive and Delete (Rough Cut)

By Rich

In our last post in this series, we covered the cloud implications of the Share phase of Data Security Cycle. In this post we will move on to the Archive and Destroy phases.

Archive

Definition

Archiving is the process of transferring data from active use into long-term storage. This can include archived storage at your cloud provider, or migration back to internal archives.

From a security perspective we are concerned with two controls: encrypting the data, and tracking the assets when data moves to removable storage (tapes, or external drives for shipping transfers). Since many cloud providers are constantly backing up data, archiving often occurs outside customer control, and it’s important to understand your provider’s policies and procedures.

Steps and Controls

ControlStructured/ApplicationUnstructured
EncryptionDatabase EncryptionTape Encryption
Storage Encryption
Asset ManagementAsset Management

Encryption

In the Store phase we covered a variety of encryption options, and if content is kept encrypted as it moves into archived storage, no additional steps are needed. Make sure your archiving system takes the encryption keys into account, since restored data is useless if the corresponding decryption keys are unavailable. In cloud environments data is often kept live due to the elasticity of cloud storage, and might just be marked with some sort of archive tag or metadata.

  1. Database Encryption: We reviewed the major database encryption options in the Store phase. The only archive-specific issue is ensuring the database replication/archiving method supports maintenance of the existing encryption. Another option is to use file encryption to secure the database archives. For larger databases, tape or storage encryption is often used.
  2. Tape Encryption: Encryption of the backup tapes using either hardware or software. There are a number of tools on the market and this is a common practice. Hardware provides the best performance, and inline appliances can work with most existing tape systems, but we are increasingly seeing encryption integrated into backup software and even tape drives. If your cloud provider manages tape backups (which many do), it’s important to understand how those tapes are protected – is any existing encryption maintained, and if not, how are the tapes encrypted and keys managed?
  3. Storage Encryption: Encryption of data archived to disk, using a variety of techniques. Although some hardware tools such as inline appliances and encrypted drivesxist, this is most commonly performed in software. We are using Storage Encryption as a generic term to cover any file or media encryption for data moved to long-term disk storage.

Asset Management

One common problem in both traditional and cloud environments is the difficulty of tracking the storage media containing archived data. Merely losing the location of unencrypted media may require a breach disclosure, even if the tape or drive is likely still located in a secure area – if you can’t prove it’s there, it is effectively lost. From a security perspective, we aren’t as concerned with asset management for encrypted content – it’s more of an issue for unencrypted sensitive data. Check with your cloud provider to understand their asset tracking for media, or implement an asset management system and procedures if you manage your own archives of cloud data.

Cloud SPI Tier Implications

Software as a Service (SaaS)

Archive security options in a SaaS deployment are completely dependent on your provider. Determine their backup procedures (especially backup rotations), any encryption, and asset management (especially for unencrypted data). Also determine if there are any differences between backups of live data and any long-term archiving for data moved off primary systems.

Platform as a Service (PaaS)

Archive security in PaaS deployments is similar to SaaS when you transition data to, or manage data with, the PaaS provider. You will need to understand the provider’s archive mechanisms and security controls. If the data resides in your systems, archive security is no different than managing secure archives for your traditional data stores.

Infrastructure as a Service (IaaS)

For completely private cloud deployments, IaaS Archive security is no different than managing traditional archived storage. You’ll use some form of media encryption and asset management for sensitive data. For cloud storage and databases, as with PaaS and SaaS you need to understand the archival controls used by your provider, although any data encrypted before moving to the cloud is clearly still secure.

Destroy

Definition

Destroy is the permanent destruction of data that’s no longer needed, and the use of content discovery to validate that it is not lingering in active storage or archives.

Organizations commonly destroy unneeded data, especially sensitive data that may be under regulatory compliance requirements. The cloud may complicate this if your provider’s data management infrastructure isn’t compatible with your destruction requirements (e.g., the provider is unable to delete data from archived storage). Crypto-shredding may be the best option for many cloud deployments, since it relies less on complete access to all physical media, which may be difficult or impossible even in completely private/internal cloud deployments.

Steps and Controls

ControlStructured/ApplicationUnstructured
Crypto-ShreddingEnterprise Key Management
Secure DeletionDisk/Free Space Wiping
Physical DestructionPhysical Destruction
Content DiscoveryDatabase DiscoveryDLP/CMP Discovery
Storage/Data Classification Tools
Electronic Discovery

Crypto-Shredding

Crypto-shredding is the deliberate destruction of all encryption keys for the data; effectively destroying the data until the encryption protocol used is (theoretically, some day) broken or capable of being brute-forced. This is sufficient for nearly every use case in a private enterprise, but shouldn’t be considered acceptable for highly sensitive government data. Encryption tools must have this as a specific feature to absolutely ensure that the keys are unrecoverable. Crypto-shredding is an effective technique for the cloud since it ensures that any data in archival storage that’s outside your physical control is also destroyed once you make the keys unavailable. If all data is encrypted with a single key, to crypto-shred you’ll need to rotate the key for active storage, then shred the “old” key, which will render archived data inaccessible.

We don’t mean to oversimplify this option – if your cloud provider can’t rotate your keys or ensure key deletion, crypto-shredding isn’t realistic. If you manage your own keys, it should be an important part of your strategy.

Disk/Free Space Wiping and Physical Destruction

These options is only available when you have low-level administrative access to the physical storage. It includes software or hardware designed to destroy data on hard drives and other media, or physical destruction of the drives. At a minimum the tool should overwrite all writable space on the media 1-3 times, and 7 times is recommended for sensitive data. Merely formatting over data is not sufficient. Secure wiping is highly recommended for any systems with sensitive data that are sold or reused, especially laptops and desktops. File-level secure deletion tools exist for when it’s necessary to destroy just a portion of data in active storage, but are not as reliable as a full media wipe.

For physical destruction (again, assuming you have access to the drives), there are two options:

  1. Degaussing: Use of strong magnets to scramble magnetic media like hard drives and backup tapes. Dedicated solutions should be used to ensure data is unrecoverable, and it’s highly recommended you confirm the efficiency of a degaussing tool by randomly performing forensic analysis on wiped media.
  2. Physical Destruction: Complete physical destruction of storage devices, focusing on shredding the actual magnetic media (platters or tape).

Due to the abstraction involved in cloud computing, these will often not be available, although your provider may include them as part of their procedures for management of their drives. When managing a private/internal cloud, you can include physical media wiping or destruction as part of your procedures for managing drives removed from active service. In IaaS deployments, you may retain the low level access to overwrite data in individual virtual machines or storage.

Content Discovery

When truly sensitive data reaches end-of-life, you need to make sure that the destroyed data is really destroyed. Use of content discovery tools helps ensure that no copies or versions of the data remain accessible in the enterprise. Considering how complex our storage, archive, and backup strategies in the cloud are today, it is impossible to absolutely guarantee the data is unrecoverable, but content discovery does reduce the risk of retrieval.

As with content discovery in the Store phase, these tools are only effective if they have access to the storage infrastructure; they cannot work through an application interface unless they are built into the application.

For details on Database Discovery and DLP/CMP please see the Store phase. There are two additional technology categories we also see used for this purpose:

  1. Storage/Data Classification and Search: These are tools typically used and managed by enterprise storage teams. Their content analysis is generally less detailed than DLP/CMP tools, but can be helpful for broad searches for stored data. Storage/Data classification tools are third-party tools which crawl a storage environment and use rule sets (usually keywords and regular expressions) to apply metadata tags to files. If your cloud storage offers standard file access, they may be helpful. Search is either built into the application or a third-party tool that indexes stored data. While these are not ideal tools for content discovery to ensure data destruction, search may be your only option in some SaaS deployments.
  2. Electronic Discovery: Tools dedicated to the electronic discovery of data for legal proceedings. Likely the same tools that will be used to search for destroyed data if there’s ever reason to attempt recovery in the future. As with most of the tools in this section, they are not cloud specific and may not be an option.

Cloud SPI Tier Implications

Software as a Service (SaaS)

As with Archive, your data destruction options are completely dependent on your provider. Typically you will be limited to some level of deletion, although in some applications crypto-shredding may be an option. What’s most important is to understand how your provider handles data destruction, and to obtain any documentation and service level agreements that are available. Search will usually be your best content discovery option.

Platform as a Service (PaaS)

For data stored with your PaaS provider, unless you have file system access of some sort you will face the same limitations as with SaaS providers. If you encrypt data on your side before sending it to the platform, crypto-shredding is a good option. Any data stored in your environment is obviously easier to destroy, since you have greater control of the infrastructure and physical media. Content discovery may be an option, but this depends completely on how your PaaS-based application is designed.

Infrastructure as a Service (IaaS)

For cloud data storage (database and file based), crypto-shredding is likely your best option. For other infrastructure deployments, particularly those with virtual machines and disks, you may be able to overwrite stored data. Content discovery using DLP/CMP will probably work, again depending on the details of your deployment.

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