Secure Deletion Guideline

UC Berkeley security policy mandates compliance with Minimum Security Standard for Electronic Information for devices handling covered data.  The recommendations below are provided as optional guidance to assist with achieving the Secure File Deletion requirement

Requirement

Resource Custodians must ensure that electronic devices storing covered data are sanitized in accordance with the UC Berkeley’s Minimum Security Standards for Electronic Information (MSSEI). This includes securely overwriting, wiping, or encrypting and deleting the encryption key for devices being repurposed, transferred, or recycled. If media cannot be effectively sanitized (e.g., defective drives, optical media), it must be physically destroyed before disposal.

Description of Risk

Storage media are vulnerable to theft, loss, and unauthorized reuse. If data is not properly deleted, sensitive information may be recovered from discarded or repurposed devices.

Recommendations

During a covered device’s lifecycle, it may need to be retired for various reasons such as upgrades, migration or project closing. To avoid covered data remnants from being accessed by unauthorized parties in legacy covered devices, follow the recommendations below to delete covered data before retiring the covered device.

Sanitization Prior to Device Reuse

During a covered device’s lifecycle, it may need to be retired due to upgrades, migration, or project closure. To prevent unauthorized access to covered data, devices must be sanitized before reuse or retirement.

• Use software that overwrites data with multiple passes (e.g., DoD 3 pass overwrite standard (DoD 5220.22-M)) or performs Secure Erase.
• Sanitize the entire disk, not just individual files, when feasible.
• Use disk deletion tools when retiring or repurposing an entire drive. Use file deletion tools when securely deleting individual files or folders on devices that will remain in use.

Hard Disk Drives (HDDs)

HDDs are spinning disk drives commonly found in servers, large storage arrays, and some older desktops or laptops. These drives store data magnetically on physical platters, which makes them well-suited for software-based or magnetic sanitization methods.

Recommended practices for HDD sanitization:

• Use multi-pass overwrite tools (e.g., 3-pass or 7-pass) to sanitize the drive in compliance with NIST SP 800-88 Rev. 1.
  
   
• Approved tools such as BitRaser and BCWipe support secure overwriting of HDDs.
  
   
• If the drive is no longer functional or cannot be overwritten:
  
   
  • Degauss the drive using a certified degausser to irreversibly disrupt the magnetic field and render the data unrecoverable.
    
     
  • Alternatively, or in addition, physically destroy the drive (e.g., shredding or crushing the platters).
    
     
• Document all sanitization or destruction steps per your unit’s data handling procedures and UC Berkeley’s MSSEI policy.
  
   

🔒 Note: Degaussing is highly effective for HDDs but is not appropriate for SSDs, which do not store data magnetically.

 

Solid-State Drives (SSDs), Flash Drives, and SD Cards

Secure deletion tools that overwrite sectors may not fully sanitize flash-based media due to wear leveling and data remapping, which prevent consistent overwriting of physical storage locations.

Best practice for flash-based media:

• Enable Full Disk Encryption (FDE) at initial setup.
  
   
• Use firmware-level Secure Erase tools when available.
  
   
• For retirement, follow physical destruction guidance per NIST SP 800-88 Rev. 2.
  
   
• Additional info: EFF: SSD Secure Deletion
  
   

Below are list of recommended software tools for disk and file deletion.  Use disk deletion tools when you need to erase the content of an entire disk drive, such as when you are retiring a disk drive, or the computer itself.  Or you want to repurpose your computer by re-installing/upgrading your operating system.  Use file deletion if you want to continue to use the computer as-is, but want to delete specific files or folders containing covered data.

Recommended Secure Deletion Tools

Disk Deletion Tools

File Deletion Tools

⚠️ Note: srm and Secure Empty Trash have been removed in modern macOS versions. Use Disk Utility or enable FileVault full disk encryption before wiping.

Solid-State Drives (SSDs), Flash Drives, and SD Cards

Traditional deletion tools may not fully sanitize flash storage. Instead:

• Use Full Disk Encryption (FDE) from the outset.
• To retire SSDs or flash media, follow physical destruction recommendations from NIST SP 800-88 Rev. 2.

Read more at the Electronic Frontier Foundation (EFF): SSD Secure Deletion

Sanitization Prior to Device Disposal

1. Physically remove storage media from the device.
2. Shred or destroy the storage media following the guidance in NIST SP 800-88 Rev. 1 – Appendix A.

Additional Resources

• UC Berkeley Minimum Security Standards for Electronic Information (MSSEI)
• NIST SP 800-88 Revision 2 – Guidelines for Media Sanitization
• EFF: How to Securely Delete Files