Secure coding technique: Securely deleting files
Deleting files on a computer system is tricky. Everybody, even your mother, has deleted a file too many before and has been happy to find it still in the trash and able to recover it.
Data in computer systems is represented by a sequence of bits. That means the system needs to do some bookkeeping within the file system to know which bits represent which file. Among this information is the size of the file, the time it was last modified, its owner, access permissions and so on. This bookkeeping data is stored separately from the contents of the file.
Usually, when a file is removed nothing happens to the bits representing the file, but the bookkeeping data is changed so that the system knows this part of the storage is now meaningless and can be reused. Until another file is saved in this location and the bits in this location are overwritten, you can often still recover the data that was saved. This not only improves the speed of deleting files but is often a useful feature to undo the deletion.
However, there are downsides to this approach. When an application on a computer system handles sensitive information it will save this data somewhere on the file system. At some point, when the information is no longer needed, this data may be deleted. If no extra care is taken this data may still be recoverable even though the intention of the developer was that all data was deleted.
The easiest way to completely erase that data is to rewrite the file content with random data (sometimes even several times over). There are several existing methods of secure file removal and they vary across storage types and file systems such as the Gutmann method. However, for day to day application use, these are a bit overkill and you can just overwrite the data yourself.
Be careful though! Do not use all zeros or other low entropy data. Many filesystems may optimize writing such sparse files and leave some of the original content. It is recommended to generate securely random data to overwrite the entire file contents before deleting the file itself.
Data remanence is the residual physical representation of data that has been in some way erased. After storage media is erased there may be some physical characteristics that allow data to be reconstructed.
Data remanence is the residual physical representation of data that has been in some way erased.
Application Security Researcher - R&D Engineer - PhD Candidate
Secure Code Warrior is here for your organization to help you secure code across the entire software development lifecycle and create a culture in which cybersecurity is top of mind. Whether you’re an AppSec Manager, Developer, CISO, or anyone involved in security, we can help your organization reduce risks associated with insecure code.
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Application Security Researcher - R&D Engineer - PhD Candidate
Deleting files on a computer system is tricky. Everybody, even your mother, has deleted a file too many before and has been happy to find it still in the trash and able to recover it.
Data in computer systems is represented by a sequence of bits. That means the system needs to do some bookkeeping within the file system to know which bits represent which file. Among this information is the size of the file, the time it was last modified, its owner, access permissions and so on. This bookkeeping data is stored separately from the contents of the file.
Usually, when a file is removed nothing happens to the bits representing the file, but the bookkeeping data is changed so that the system knows this part of the storage is now meaningless and can be reused. Until another file is saved in this location and the bits in this location are overwritten, you can often still recover the data that was saved. This not only improves the speed of deleting files but is often a useful feature to undo the deletion.
However, there are downsides to this approach. When an application on a computer system handles sensitive information it will save this data somewhere on the file system. At some point, when the information is no longer needed, this data may be deleted. If no extra care is taken this data may still be recoverable even though the intention of the developer was that all data was deleted.
The easiest way to completely erase that data is to rewrite the file content with random data (sometimes even several times over). There are several existing methods of secure file removal and they vary across storage types and file systems such as the Gutmann method. However, for day to day application use, these are a bit overkill and you can just overwrite the data yourself.
Be careful though! Do not use all zeros or other low entropy data. Many filesystems may optimize writing such sparse files and leave some of the original content. It is recommended to generate securely random data to overwrite the entire file contents before deleting the file itself.
Data remanence is the residual physical representation of data that has been in some way erased. After storage media is erased there may be some physical characteristics that allow data to be reconstructed.
Deleting files on a computer system is tricky. Everybody, even your mother, has deleted a file too many before and has been happy to find it still in the trash and able to recover it.
Data in computer systems is represented by a sequence of bits. That means the system needs to do some bookkeeping within the file system to know which bits represent which file. Among this information is the size of the file, the time it was last modified, its owner, access permissions and so on. This bookkeeping data is stored separately from the contents of the file.
Usually, when a file is removed nothing happens to the bits representing the file, but the bookkeeping data is changed so that the system knows this part of the storage is now meaningless and can be reused. Until another file is saved in this location and the bits in this location are overwritten, you can often still recover the data that was saved. This not only improves the speed of deleting files but is often a useful feature to undo the deletion.
However, there are downsides to this approach. When an application on a computer system handles sensitive information it will save this data somewhere on the file system. At some point, when the information is no longer needed, this data may be deleted. If no extra care is taken this data may still be recoverable even though the intention of the developer was that all data was deleted.
The easiest way to completely erase that data is to rewrite the file content with random data (sometimes even several times over). There are several existing methods of secure file removal and they vary across storage types and file systems such as the Gutmann method. However, for day to day application use, these are a bit overkill and you can just overwrite the data yourself.
Be careful though! Do not use all zeros or other low entropy data. Many filesystems may optimize writing such sparse files and leave some of the original content. It is recommended to generate securely random data to overwrite the entire file contents before deleting the file itself.
Data remanence is the residual physical representation of data that has been in some way erased. After storage media is erased there may be some physical characteristics that allow data to be reconstructed.
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Secure Code Warrior is here for your organization to help you secure code across the entire software development lifecycle and create a culture in which cybersecurity is top of mind. Whether you’re an AppSec Manager, Developer, CISO, or anyone involved in security, we can help your organization reduce risks associated with insecure code.
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Application Security Researcher - R&D Engineer - PhD Candidate
Deleting files on a computer system is tricky. Everybody, even your mother, has deleted a file too many before and has been happy to find it still in the trash and able to recover it.
Data in computer systems is represented by a sequence of bits. That means the system needs to do some bookkeeping within the file system to know which bits represent which file. Among this information is the size of the file, the time it was last modified, its owner, access permissions and so on. This bookkeeping data is stored separately from the contents of the file.
Usually, when a file is removed nothing happens to the bits representing the file, but the bookkeeping data is changed so that the system knows this part of the storage is now meaningless and can be reused. Until another file is saved in this location and the bits in this location are overwritten, you can often still recover the data that was saved. This not only improves the speed of deleting files but is often a useful feature to undo the deletion.
However, there are downsides to this approach. When an application on a computer system handles sensitive information it will save this data somewhere on the file system. At some point, when the information is no longer needed, this data may be deleted. If no extra care is taken this data may still be recoverable even though the intention of the developer was that all data was deleted.
The easiest way to completely erase that data is to rewrite the file content with random data (sometimes even several times over). There are several existing methods of secure file removal and they vary across storage types and file systems such as the Gutmann method. However, for day to day application use, these are a bit overkill and you can just overwrite the data yourself.
Be careful though! Do not use all zeros or other low entropy data. Many filesystems may optimize writing such sparse files and leave some of the original content. It is recommended to generate securely random data to overwrite the entire file contents before deleting the file itself.
Data remanence is the residual physical representation of data that has been in some way erased. After storage media is erased there may be some physical characteristics that allow data to be reconstructed.
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Application Security Researcher - R&D Engineer - PhD Candidate
Secure Code Warrior is here for your organization to help you secure code across the entire software development lifecycle and create a culture in which cybersecurity is top of mind. Whether you’re an AppSec Manager, Developer, CISO, or anyone involved in security, we can help your organization reduce risks associated with insecure code.
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The Power of OpenText Application Security + Secure Code Warrior
OpenText Application Security and Secure Code Warrior combine vulnerability detection with AI Software Governance and developer capability. Together, they help organizations reduce risk, strengthen secure coding practices, and confidently adopt AI-driven development.
Secure Code Warrior corporate overview
Secure Code Warrior is an AI Software Governance platform designed to enable organizations to safely adopt AI-driven development by bridging the gap between development velocity and enterprise security. The platform addresses the "Visibility Gap," where security teams often lack insights into shadow AI coding tools and the origins of production code.
Secure code training topics & content
Our industry-leading content is always evolving to fit the ever changing software development landscape with your role in mind. Topics covering everything from AI to XQuery Injection, offered for a variety of roles from Architects and Engineers to Product Managers and QA. Get a sneak peek of what our content catalog has to offer by topic and role.
Cyber Resilience Act (CRA) Aligned Learning Pathways
SCW supports Cyber Resilience Act (CRA) readiness with CRA-aligned Quests and conceptual learning collections that help development teams build the Secure by Design, SDLC, and secure coding skills aligned with the CRA’s secure development principles.
Resources to get you started
Observe and Secure the ADLC: A Four-Point Framework for CISOs and Development Teams Using AI
While development teams look to make the most of GenAI’s undeniable benefits, we’d like to propose a four-point foundational framework that will allow security leaders to deploy AI coding tools and agents with a higher, more relevant standard of security best practices. It details exactly what enterprises can do to ensure safe, secure code development right now, and as agentic AI becomes an even bigger factor in the future.
