NIST Purge, Clear and Destroy: Difference Explained

There are so many ways to destroy data and sanitise storage media. But which one is best?

Well, there isn’t one correct answer for this. Rather, it depends on factors like:

• Sensitivity of data
• Type of device
• Whether you’ll use the device again or not
• Guidelines of prevalent data protection and sanitization standards
• And a lot more

In this guide, we’ve explained the differences between Purge, Clear, and Destroy – the three methods of data destruction under the NIST SP 800-800 standard. 

Purge vs Clear vs Destroy. Read on to find out. 

What is NIST SP 800-88 Media Sanitisation Standard?

NIST SP 800-88 is considered the golden standard for data sanitisation. 

NIST stands for National Institute of Standards and Technology. It is a physical science laboratory and an agency of the US Department of Commerce. 

The NIST 800-88 draws guidelines on how to erase data from a device such that it is non-recoverable. Under NIST 800-88, there are three categories of data destruction. These are Clear, Purge, and Destroy. 

Read on to know the distinctions between the three types of data destruction.

Purge vs. Clear vs. Destroy

Besides the device in question, the sensitivity of the data is also a deciding factor for choosing whether to use Clear, Purge or Destroy. Here is a map of how the decision is made.

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What is Purge as defined in NIST 800-88?

Purge is a method of data sanitisation that uses both logical and physical methods to erase data. And the key requirement is that data recovery should become infeasible. 

Under Purge, both overwriting and physical destruction are acceptable destruction techniques. 

NIST Purge is usually conducted in a laboratory environment. Methods like overwriting, block erasure, and cryptographic erasure are applied under Purge. All of these are logical destruction methods. So the drive can be reused. Here are some methods used in the purge method. 

• Overwriting: Either one or three overwriting passes are used to make data recovery impossible. 
• Block Erase: Here, each block of the storage devices is deleted electrically. After one pass of the block erase method, binary 1s are applied over the user-addressable locations. Then block erasure is performed again. 
• Cryptographic Erase: The Media Encryption Keys (MEKs) are sanitised. This makes the data non-retrievable. 

Physical destruction techniques like shreddings, degaussing, and pulverising are also used. These render the device unusable. So technically the data is irrecoverable. But physical destruction techniques are not cost-efficient or environment friendly. 

What is NIST Clear as defined in NIST 800-88?

NIST Clear is typically used with non-sensitive data. The method employs standard read and write commands to overwrite the data on the disk. 

For data destruction to be effective, all the user addressable locations on a disk must be destroyed. 

Overwriting can only be done if there is no physical damage to the disk. Overwriting, sometimes, isn’t possible on all areas of the device to be sanitised. That is why this technique is usually used with less sensitive data. 

What is Destroy as defined in NIST 800-88?

The destroy method is often used as a last resort when purge and clear aren’t possible alternatives. It is also used when the data destruction verification with purge and clear techniques fail. 

Under this method, the media isn’t considered fully sanitised unless data retrieval is proven to be infeasible using state-of-the-art laboratory techniques. Here are some techniques that are used to destroy devices. 

• Disintegrate
• Pulverize
• Incinerate 
• Melt 

All of these techniques will completely destroy the device. Because of this, it is not possible to verify whether data destruction was successful.

Comparision Between Purge, Clear and Destroy?

Among purge, clear, and destroy, you have three equally robust data eraser techniques. When you know your erasure requirements better, then you can know which of these suits your purpose the best. 

Purge vs Clear

Purge vs Destroy 

Clear vs Destroy 

In the argument of purge vs clear vs destroy, the answer depends on the type of device to sanitise. 

Let’s understand with the help of an example.

NIST 800-88 for ATA Hard Disk Drives

ATA, or Advanced Technical Attachment hard disks allow the disk to be connected to the motherboard of your PC. It can also perform basic input/output functions. Here is how you can sanitise the drive.

If you’re choosing a software-based data wiping method, then you can sanitise the device in-house. Some software can also be automated.

So if you need to sanitise a device without too much of a hassle, then software-based methods, like purge and clear would be the best.

We hope this guide helped you understand NIST 800-88 in the context of Purge, Clear, and Destroy as three data destruction techniques.