Lawful Interception via Key Management Service Storage
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Solution Overview
Problem
Current lawful interception methods for MIKEY-TICKET key exchange protocols in encrypted communications are detectable and cannot perform mid-call interception due to discarded key information, breaking the requirement for undetectable and seamless interception.
Innovation Solution
The solution involves storing unique secret keys and nonce values in a secure database accessible by the Key Management Service (KMS), allowing regeneration of encryption keys through the SRTP Master Key Identifier (MKI) field, enabling lawful interception without re-keying and maintaining secrecy by encrypting these values.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If keying information (RANDRi, CS ID, TGK) is discarded by the KMS after replying to the initiator UE, then security is maintained through proper key management, but mid-call interception becomes impossible without detectable re-keying
Solution Approach 1:
The KMS stores keying information (RANDRi, CS ID, TGK) in advance before the communication session ends. This preliminary storage action ensures that the information remains available for future lawful interception requests without affecting the normal key management process or requiring detectable re-keying operations during mid-call interception.
2Reliability
If re-keying is performed to enable lawful interception, then key information becomes available for decryption, but the interception becomes detectable by the initiator UE and responder UE
Solution Approach 1:
The KMS creates and stores a copy of the keying information (RANDRi, CS ID, TGK) in its database during the normal key establishment process. This copying allows the KMS to provide decryption capabilities for lawful interception without performing any additional re-keying operations that would be detectable by the communicating parties. The stored copy serves as a silent backup for interception purposes.
3Reliability
If keying information is stored in the KMS database, then mid-call interception without re-keying becomes possible, but the database security and access control become more critical
Solution Approach 1:
The KMS acts as an intermediary between the normal communication parties and the lawful interception authorities. It stores keying information in its secure database and controls access to this information through authenticated requests from law enforcement agencies. This intermediary role centralizes the security management burden in the KMS, allowing other network elements to perform interception functions without directly handling sensitive keying information.
Data Source
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AI summary
A method of decrypting an intercepted message, the method comprising receiving one or more values used in generation of an encryption key, storing the one or more values used by a KMF to regenerate the encryption key, generating the encryption key using the one or more values, signalling a start_interception message to a CSCF, decrypting intercepted packets and signalling a halt message from an ADMF to the CSCF.