Cryptographic Key Generation for LTE Security
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The existing cryptographic key derivation functions in 3GPP SAE/LTE networks face challenges in ensuring uniqueness, leading to potential collisions due to the use of symmetric cryptography and permutation-based algorithms like AES, which fail to guarantee unique inputs, compromising security, especially in beyond-3G communication networks.
Innovation Solution
A method is introduced that generates cryptographic keys by applying a key derivation function to a concatenation of a Sequence Number (SQN) and an Anonymity Key (AK) along with a Message Authentication Code (MAC), ensuring unique inputs each time the security operation is initiated, thereby avoiding collisions and enhancing security.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a key derivation function based on SHA-256 is used with CK and IK as inputs, then the cryptographic key generation is secure and collision-resistant, but the uniqueness of inputs cannot be guaranteed leading to potential collisions between different UEs or repeated authentications
Solution Approach 1:
The patent segments the KDF input into multiple distinct components: CK, IK, SQN, and AUTN. By dividing the input space into these segments, the system ensures that each authentication instance has a unique input combination, preventing collisions even when CK and IK alone might repeat.
Solution Approach 2:
The patent adds new dimensions to the KDF input space by incorporating SQN (sequence number) and AUTN (authentication token) alongside CK and IK. This dimensional expansion transforms the input from a 2-component vector (CK, IK) to a 4-component vector, dramatically increasing the input space and ensuring uniqueness across different authentication instances.
2Productivity
If the same CK is generated for different UEs or repeated authentications, then the key derivation process is efficient and simple, but collision resistance is compromised and security is undermined
Solution Approach 1:
The patent applies preliminary action by pre-incrementing the SQN before each authentication and embedding it in the AUTN token. This preliminary preparation ensures that even before the KDF is executed, the input is guaranteed to be unique, preventing any possibility of collision while maintaining the efficiency of the key derivation process.
Solution Approach 2:
The patent introduces AUTN as an intermediary element that mediates between the authentication state (SQN) and the key derivation function. This intermediary carries the uniqueness information from SQN into the KDF input, ensuring collision resistance without requiring changes to the core key derivation algorithm or reducing its efficiency.
3Ease of manufacture
If existing USIMs are used without modification, then deployment cost is reduced and compatibility is maintained, but the higher security requirements of SAE/LTE networks cannot be met
Solution Approach 1:
The patent makes the existing USIM multi-functional by enabling it to not only store CK and IK but also to generate and process SQN and AUTN. This universality allows the same hardware token to support both legacy UMTS security and new SAE/LTE security requirements, eliminating the need for separate USIM versions or additional hardware.
Solution Approach 2:
The patent achieves enhanced security through parameter changes rather than structural changes. By modifying the KDF input parameters to include SQN and AUTN, and by changing the key derivation formula, the system meets SAE/LTE security requirements while the physical USIM hardware remains unchanged, maintaining ease of deployment.
Data Source
Figure 1~2
Figure 3~5
Figure 6~7
AI summary
A technique for generating a cryptographic key (120) is provided. The technique is particularly useful for protecting the communication between two entities (202, 302; 204, 304) cooperatively running a distributed security operation. The technique comprises providing an input to a key derivation function, the input comprising at least two parameters (106, 108), the first parameter (106) comprising or derived from some cryptographic keys (110, 112) which have been computed by the first entity (202, 302) by running the security operation and the second parameter (108) comprising or derived from a token (116) computed by the second entity (204, 304) for the first entity (202, 302) by running the security operation. The key derivation function is applied to the provided input to generate the desired cryptographic key (120).