Key Management System for Permanent Data Deletion
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Solution Overview
Problem
Existing methods for making data unrecoverable, such as email, face challenges in ensuring that data is reliably deleted from backup media and forensic recovery, and require expensive tamper-resistant smart cards for secure key management.
Innovation Solution
A system that manages secret keys by generating a hash of a nonce and a secret associated with an expiration time, allowing the server to reconstruct the encryption key without maintaining per-message state information, and storing secrets on a tamper-resistant smart card for secure key management.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If data is stored in encrypted form with per-message keys, then data security is improved, but key management complexity and storage requirements increase
Solution Approach 1:
The patent extracts the key management function from the message processing system by introducing a separate key-issuing server. This server generates and manages encryption keys independently, allowing message encryption/decryption systems to focus solely on their core function while relying on the dedicated key management infrastructure.
Solution Approach 2:
The key-issuing server acts as an intermediary between message senders and receivers. Instead of users directly managing encryption keys, they request keys from this intermediary service, which handles key generation, distribution, and revocation. This mediator simplifies user operations while maintaining strong security.
2Reliability
If tamper-resistant smart cards are used for key storage, then key security is improved, but device cost and complexity increase
Solution Approach 1:
The patent uses cryptographic copying rather than physical duplication. Instead of requiring physical smart cards, the system uses mathematical key derivation to create functional copies of encryption capabilities. The master key can derive multiple message keys through cryptographic operations, achieving the security of multiple physical keys without the physical infrastructure.
Solution Approach 2:
The patent replaces the mechanical/physical key storage system (smart cards, tamper-resistant devices) with a computational key derivation system. Instead of physically protecting keys through hardware, the system uses cryptographic algorithms to protect keys through mathematical complexity, substituting physical security mechanisms with computational security.
3Ease of operation
If keys are stored on a server for retrieval, then key accessibility is improved, but server storage requirements increase
Solution Approach 1:
The system performs preliminary key generation and stores only the essential master key on the server. Rather than storing all possible message keys, the master key is prepared in advance and can derive any number of message keys as needed. This preliminary action reduces server storage to just one key regardless of the number of messages.
Solution Approach 2:
The patent changes the parameter of key storage from storing multiple message keys to storing a single master key with key derivation capability. By changing from storing N message keys to storing 1 master key that can generate N message keys, the storage requirement changes from O(N) to O(1).
Data Source
AI summary
One embodiment of the present invention provides a system that manages secret keys for messages. During operation, the system receives a desired expiration time T from an encrypter, and possibly a nonce N, at a server that manages keys. If N is not sent by the encrypter, it is generated by a key managing server. Next, the system chooses a secret ST, with an expiration time close to T, and an identifier IDS from a database for which secret ST can be retrieved using the identifier IDS. If such an ST is not already in the database, the server generates a new ST and IDS. The system then calculates a hash H=h(N,ST), and sends H and IDS from the server to the encrypter. The encrypter then encrypts M with H to form {M}H, and communicates ({M}H, N, IDS) to a message reader. The message reader then sends N and IDS to the server. The server then uses IDS to lookup ST, recalculates H=h(N,ST), and sends H to the message reader, thereby enabling the message reader to decrypt {M}H to obtain M. Note that by using the secret ST associated with the expiration time T and the nonce N, the server is able to reconstruct the secret key H for the message M without having to maintain per-message state information.