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---
title: "Application Data Storage"
sidebar:
label: Application Data Storage
---
GpgFrontend employs a robust and secure approach for storing application data,
especially for sensitive or dynamic information such as key server settings, key
generation profiles, and other internal objects.
> Note: Prior to version 2.1.9, application data encryption was handled
> differently: The reference for each data object was generated by simply
> computing the SHA-256 hash of the master application key combined with the
> object name. All objects were encrypted directly with the master key, without
> per-object key derivation, HMAC, or authenticated encryption modes. Advanced
> techniques such as HKDF-based key derivation, per-object HMAC, and
> authenticated encryption (e.g., AES-GCM) were introduced in v2.1.9 for
> significantly improved security.
## Data Object Structure
- Unique Reference: Each piece of application data is associated with a unique
reference, generated using an HMAC-SHA256 digest of the object name (or a
random value for unnamed objects) and a legacy key. This ensures both
uniqueness and integrity of the data mapping.
- Per-Object Encryption: Every data object is encrypted individually using a key
derived from the current active application secure key and the object’s
reference. Key derivation utilizes HKDF-SHA256 for high security and
resistance to key reuse attacks.
- Key Identification: The first part of each stored object file contains an
identifier for the key used to encrypt it, allowing for seamless key rotation
and backward compatibility.
- Encryption Algorithms: Actual data encryption uses lightweight, authenticated
cryptography (such as AES-GCM or an equivalent mode), ensuring both
confidentiality and integrity of application objects.
## File Layout and Access
- Storage Location: All encrypted data objects are stored in the `data_objs/`
subdirectory within the application’s data directory.
- File Naming: Encrypted objects are stored as files named after the hexadecimal
encoding of their reference value. This obfuscates file content and prevents
direct association with plaintext object names.
- Data Separation: Data created under different SecureLevels or key environments
is logically separated, providing clear isolation between different security
contexts.
- Secure Key Retrieval: On access, the application retrieves the correct
encryption key for each data object using its embedded key identifier, and
securely derives the per-object key to decrypt or update the content.
- Atomic Updates: Data updates are handled in a manner that prevents corruption
or partial writes, ensuring data integrity even in the event of application or
system interruptions.
## Security Considerations
- Strong Isolation: Per-object encryption and unique key derivation mean that
compromise of one data object does not impact the security of others.
- Key Rotation Support: When application keys are rotated, existing objects
remain accessible through their associated key identifiers, supporting smooth
transitions and automated data migration.
- User Transparency: All encryption, decryption, and data migration processes
are handled transparently by GpgFrontend, requiring no manual intervention
from users in regular workflows.
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