KMS Secure Database for Undetectable SRTP Interception

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Solution Overview

Problem

Current lawful interception methods for MIKEY-TICKET based SRTP communications are detectable and unable to perform mid-call interception due to discarded key regeneration information, violating the requirement of undetectable interception and efficient key management.

Innovation Solution

The proposed solution involves storing and regenerating encryption keys using a unique secret key and nonce value in the SRTP Master Key Identifier field, allowing law enforcement agencies to intercept communications by re-generating the Traffic Encryption Key without disrupting the communication process.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If key regeneration information is discarded by the KMS after replying to the initiator UE, then security is improved by preventing key compromise, but lawful interception capability deteriorates because the KMS cannot regenerate the TEK for interception

Engineering Contradiction:

ImprovesecurityVSAvoidlawful interception capability

Core Design Contradiction:

ReliabilityVSAdaptability or versatility

Solution Approach 1:

The KMS performs preliminary action by storing the key regeneration information (RANDRi, CS ID, TGK) in a secure database before the communication session ends. This preliminary storage ensures that the information is preserved for potential future lawful interception requests without compromising current security operations.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

A secure database acts as an intermediary between the KMS and lawful interception requirements. The database stores the key regeneration information securely, allowing the KMS to regenerate TEKs when legally authorized while maintaining security during normal operations. The database mediates between conflicting security and interception needs.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Adaptability or versatility

If re-keying is performed for mid-call interception, then lawful access is enabled, but detectability increases and undetectable interception requirement is violated

Engineering Contradiction:

Improvelawful access capabilityVSAvoiddetectability

Core Design Contradiction:

Adaptability or versatilityVSObject-affected harmful factors

Solution Approach 1:

Instead of performing re-keying operations that would be detected, the system creates a copy of the TEK using the stored key regeneration information (RANDRi, CS ID, TGK) in the secure database. The LAF requests the KMS to regenerate the TEK, which is then provided to the law enforcement agency without the communication parties detecting any key changes.

Inventive Principle:

Principle #26Copying

Solution Approach 2:

The KMS acts as an intermediary that can regenerate the TEK based on stored information without the communication parties noticing. The LAF communicates with the KMS to obtain the regenerated TEK, bypassing the need for detectable re-keying operations in the communication stream.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Adaptability or versatility

If key regeneration information is stored in the KMS, then mid-call interception becomes possible, but system complexity increases and storage requirements increase

Engineering Contradiction:

Improvemid-call interception capabilityVSAvoidsystem complexity

Core Design Contradiction:

Adaptability or versatilityVSDevice complexity

Solution Approach 1:

The secure database in the KMS serves multiple functions: it stores key regeneration information for potential lawful interception, maintains security during normal operations, and enables TEK regeneration when legally authorized. This multi-functionality reduces the need for separate dedicated systems for each function.

Inventive Principle:

Principle #6Universality (Multi-functionality)

Solution Approach 2:

The secure database acts as an intermediary storage mechanism that simplifies the overall system architecture. Rather than implementing complex real-time key regeneration capabilities in the LAF or communication endpoints, the centralized database mediates by storing necessary information and providing it to authorized entities.

Inventive Principle:

Principle #24Intermediary (Mediator)

4Loss of information

If the KMS stores key regeneration information, then information availability for interception is improved, but loss of information decreases (information is retained)

Engineering Contradiction:

Improvekey regeneration information availabilityVSAvoidstored data volume

Core Design Contradiction:

Loss of informationVSQuantity of substance

Solution Approach 1:

The system extracts only the essential key regeneration information (RANDRi, CS ID, TGK) needed for TEK regeneration and stores it in the secure database. Non-essential data is excluded, minimizing storage requirements while maintaining the ability to regenerate keys when needed for lawful interception.

Inventive Principle:

Principle #2Taking out (Extraction)

Data Source

PatentEP2803162B1System and method of lawful access to secure communications

Publication Date: 2020.04.15 BLACKBERRY LTD

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AI summary

The present disclosure relates to systems and methods for secure communications. In some aspects, an initiator KMS receives, from an initiator UE, one or more values used in generation of an encryption key, which includes obtaining at least one value associated with a RANDRi. The initiator KMS sends the at least one value associated with the RANDRi to a responder KMS. The responder KMS generates the encryption key using the one or more values.