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Secure Application Decryption

G5 Cyber Security

TL;DR

Yes, you can create an application that decrypts data without the administrator having access to the decryption key. This is achieved through techniques like asymmetric encryption (public/private key pairs) and secure key storage outside of the application’s code or accessible server environment. The admin holds the public key for encryption but needs a separate, highly secured mechanism to obtain the private key needed for decryption.

How to Create an Application with Administrator-Protected Decryption

  1. Understand Asymmetric Encryption: This is the core principle. Unlike symmetric encryption (same key for encrypting and decrypting), asymmetric encryption uses a pair of keys:
    • Public Key: Used to encrypt data. Anyone can have this key.
    • Private Key: Used to decrypt data. This must be kept secret.
  2. Choose an Encryption Library/Algorithm: Popular choices include:
    • RSA: A widely used algorithm for secure communication.
    • ECC (Elliptic Curve Cryptography): Offers strong security with smaller key sizes.
    • Libraries: OpenSSL, Bouncy Castle (Java), cryptography (Python).
  3. Key Generation: Generate a public/private key pair. 
    # Example using OpenSSL (command line)
    openssl genrsa -out private.pem 2048
    openssl rsa -in private.pem -pubout -out public.pem
  4. Application Architecture: Design the application with these components:
    • Encryption Module: Uses the public key to encrypt data before storage or transmission. This module is part of your application code and can be freely distributed.
    • Decryption Module: Requires the private key to decrypt data. This module must be protected (see step 6).
    • Secure Key Storage: A separate, highly secured system for storing the private key. This is NOT part of your application code or accessible server environment.
  5. Encryption Process: When data needs to be encrypted:
    1. The application’s encryption module retrieves the public key.
    2. The data is encrypted using the public key.
    3. The encrypted data is stored or transmitted.
  6. Secure Private Key Storage (Critical): This is where you prevent administrator access.
    • Hardware Security Module (HSM): The most secure option. A dedicated hardware device that stores and protects the private key. Access requires physical security measures.
    • Key Management Service (KMS): Cloud-based service for managing encryption keys. Offers strong access controls and auditing. Examples: AWS KMS, Azure Key Vault, Google Cloud KMS.
    • Separate Server with Strict Access Control: If you can’t use HSM or KMS, store the private key on a dedicated server with extremely limited access (e.g., only allow decryption requests from your application server). Use strong authentication and authorization mechanisms. This is less secure than HSM/KMS.
  7. Decryption Process: When data needs to be decrypted:
    1. The application’s decryption module sends a request to the Secure Key Storage (HSM, KMS, or dedicated server).
    2. The Secure Key Storage decrypts the data using the private key. It does not expose the private key itself.
    3. The decrypted data is returned to the application.
  8. Administrator Role: The administrator can:
    • Manage access to the Secure Key Storage (e.g., grant/revoke permissions).
    • Monitor audit logs for key usage.
    • Rotate keys periodically.
    • Cannot directly decrypt data themselves without proper authorization through the secure key storage system.

Important Considerations

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