Secure Element Key Rotation for External Flash Protection
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Solution Overview
Problem
Storing sensitive information on external flash memory outside a system-on-chip (SoC) poses a risk of exposure if compromised, as it is not integrated and lacks inherent security measures.
Innovation Solution
An integrated secure element within the SoC establishes a secure channel with a secure flash for managing cryptographic keys, encrypting and decrypting data on external storage, and automatically updating keys to ensure 'perfect forward security'.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If external flash memory is used for storing sensitive information, then storage capacity and performance are improved, but security is worsened due to lack of inherent security measures
Solution Approach 1:
A secure element is introduced as an intermediary component between the external flash memory and the main processor. This secure element houses cryptographic keys and performs encryption/decryption operations, mediating access to the external storage. The secure element acts as a trust anchor that protects the external flash from direct compromise while allowing authorized access.
Solution Approach 2:
The storage system is segmented into distinct functional zones: a secure element for cryptographic operations, external flash memory for bulk storage, and a secure channel for communication between them. This segmentation isolates sensitive cryptographic material from the external storage medium, ensuring that even if the external flash is compromised, the security credentials remain protected.
2Ease of operation
If a static cryptographic key is used for securing external storage, then ease of operation is improved, but security is worsened due to vulnerability to compromise
Solution Approach 1:
The cryptographic key system transitions from static to dynamic through automatic key rotation. The secure element periodically generates and exchanges new encryption keys with the external flash memory over a secure channel. This dynamic key management ensures that compromised keys have limited validity windows and that future data remains protected even if past keys are compromised.
Solution Approach 2:
The system implements periodic key renewal cycles where cryptographic keys are automatically rotated at predetermined intervals or triggered by specific events such as data writes. This periodic action maintains forward security by ensuring that the longest any single key is valid is the key rotation period, limiting the impact of potential key compromise.
Data Source
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AI summary
An integrated secure element, of a system-on-chip, which leverages a secure channel with a secure flash to manage a cryptographic key for securing sensitive information stored on an unsecured external flash, is described. The system-on-chip stores data on a main flash, external to the system-on-chip. A second external flash is assigned to the secure element to store and manage a flash cryptographic key. The secure element and the second flash are each provisioned with matching public and private keys, and a predetermined cipher to establish a secure channel based on a shared secret key. The secure element and the second flash communicate updates to the flash cryptographic key over the secure channel. The secure element executes specialized functions including automatically encrypting data it stores on the main external flash using the flash cryptographic key as the flash cryptographic key is updated by the second external flash.