Master Key Derivation for Forward Secrecy

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Solution Overview

Problem

In secure communications, if the master key is compromised, an attacker can generate session keys and access past communications, lacking protection for previous encrypted data.

Innovation Solution

Periodically altering the master key and discarding old versions, both parties modify the master key using the same protocol, ensuring that even if the current key is compromised, previous keys remain secure, preventing decryption of intercepted communications.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If the master key is used continuously for session key derivation, then the secure communication channel can be maintained, but if the master key is compromised, all past communications can be decrypted

Engineering Contradiction:

Improvesecurity of communication channelVSAvoidvulnerability to master key compromise

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The master key is transformed from a static value to a dynamic one that periodically changes. The system derives new master key values at regular intervals using a deterministic function of the current master key, ensuring the key material evolves over time. This dynamic behavior limits the exposure window if a key is compromised and provides forward secrecy for past communications.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The master key is updated periodically through deterministic derivation rather than continuously. The system establishes a new master key value after a predetermined number of session keys have been derived or after a time interval, creating periodic key rotation that balances security with computational efficiency.

Inventive Principle:

Principle #19Periodic action

2Object-affected harmful factors

If the master key is periodically changed to provide forward secrecy, then past communications are protected, but the key management complexity increases

Engineering Contradiction:

Improveprotection against key compromiseVSAvoidkey management complexity

Core Design Contradiction:

Object-affected harmful factorsVSDevice complexity

Solution Approach 1:

The master key updates itself deterministically without external intervention. Each new master key value is derived solely from the current master key using a predetermined function, eliminating the need for complex key distribution protocols or external key management infrastructure. The system serves its own key management needs through self-derivation.

Inventive Principle:

Principle #25Self-service

Solution Approach 2:

A deterministic derivation function acts as an intermediary between the current master key and the new master key value. This mathematical function mediates the key transition, ensuring both parties derive the same new key without direct communication about the key material itself, simplifying the update protocol.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Reliability

If session keys are derived frequently from the master key, then forward secrecy is improved, but the computational overhead increases

Engineering Contradiction:

Improveforward secrecyVSAvoidcomputational energy consumption

Core Design Contradiction:

ReliabilityVSUse of energy by moving object

Solution Approach 1:

Instead of deriving a new master key after every single session key, the system derives master keys periodically after a predetermined number of session keys. This partial action approach provides sufficient forward secrecy while avoiding the excessive computational overhead of updating the master key with every session key derivation.

Inventive Principle:

Principle #16Partial or excessive action

Data Source

PatentUS9674165B2Efficient key derivation with forward secrecy

Publication Date: 2017.06.06 NXP BV

AI summary

Various embodiments relate to a method, device, and non-transitory medium including: determining a master key value for use in secure communications with a different device, wherein the master key value is used as a master key; deriving at least one session key using the master key; generating a new master key value based on the master key; deleting the current master key value; and using the new master key value as the master key.