2 cissp ® Official Study Guide Eighth Edition

Storage Media Security
We discussed the security problems that surround primary storage devices in the previous 
section. There are three main concerns when it comes to the security of secondary storage 
devices; all of them mirror concerns raised for primary storage devices:
■
Data may remain on secondary storage devices even after it has been erased. This 
condition is known as 
data remanence
. Most technically savvy computer users know 
that utilities are available that can retrieve files from a disk even after they have been 
deleted. It’s also technically possible to retrieve data from a disk that has been refor-
matted. If you truly want to remove data from a secondary storage device, you must 
use a specialized utility designed to destroy all traces of data on the device or damage 
or destroy it beyond possible repair (commonly called 
sanitizing
).
■
SSDs present a unique problem in relation to sanitization. SSD wear leveling means 
that there are often blocks of data that are not marked as “live” but that hold a copy of 
the data when it was copied off to lower wear leveled blocks. This means that a tradi-
tional zero wipe is ineffective as a data security measure for SSDs.
■
Secondary storage devices are also prone to theft. Economic loss is not the major factor 
(after all, how much does a backup tape or a hard drive cost?), but the loss of confiden-
tial information poses great risks. If someone copies your trade secrets onto a remov-
able media disc and walks out the door with it, it’s worth a lot more than the cost of 
the disc itself. For this reason, it is important to use full disk encryption to reduce the 
risk of an unauthorized entity gaining access to your data. It is good security practice 
to encrypt SSDs prior to storing any data on them due to their wear leveling technology. 
This will minimize the chance of any plaintext data residing in dormant blocks. Fortu-
nately, many HDD and SSD devices offer on-device native encryption.

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Chapter 9 
■
Security Vulnerabilities, Threats, and Countermeasures
■
Access to data stored on secondary storage devices is one of the most critical issues 
facing computer security professionals. For hard disks, data can often be protected 
through a combination of operating system access controls. Removable media pose a 
greater challenge, so securing them often requires encryption technologies.
■
As availability is also part of the security triad, it is essential to choose media that 
will retain data for the length of the time required. For instance, a backup tape might 
degrade before the retention period of the data terminates. Also, the technology used for 
secondary storage might become obsolete, making it difficult to restore/read the data.