Selective SMS Ciphering on GSM Control Channels
Solution Overview
Problem
The existing GSM system's security issue regarding the ciphering of System Information Type 5 (SI5) and Type 6 (SI6) messages on the downlink Slow Associated Control Channel (SACCH) is not adequately addressed by proposed solutions, which either compromise security or do not cipher SMS messages at all.
Innovation Solution
Implementing a method to selectively cipher SMS data blocks on the SACCH based on their content, while not ciphering other data blocks, or transmitting SMS messages on the Fast Associated Control Channel (FACCH) which is ciphered, ensuring secure transmission without compromising existing systems.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If ciphering is applied to all data blocks on SACCH, then security is improved, but processing complexity and overhead increase
Solution Approach 1:
The patent applies ciphering selectively only to SMS data blocks on SACCH rather than all data blocks. The transmitting entity determines the content type of each data block and applies ciphering only when it identifies an SMS message, while non-SMS blocks are transmitted without ciphering. This local differentiation resolves the contradiction by providing security where needed (SMS messages) while avoiding unnecessary processing complexity for other message types.
2Reliability
If ciphering is applied to SMS messages on SACCH, then security is improved, but message transmission efficiency decreases
Solution Approach 1:
The patent segments the data blocks on SACCH into different types (SMS and non-SMS) and applies different processing rules to each segment. SMS data blocks are ciphered for security, while non-SMS data blocks are transmitted without ciphering to maintain transmission efficiency. This segmentation allows the system to optimize for both security and efficiency by treating different message types differently based on their security requirements.
3Reliability
If complete de-ciphering of all data blocks is required, then security is maintained, but processing time and complexity increase
Solution Approach 1:
The transmitting entity performs preliminary identification of SMS data blocks before transmission by determining the content type of each data block. This preliminary action allows the receiving entity to know in advance which blocks require de-ciphering and which do not, eliminating the need to attempt de-ciphering all blocks. The receiving entity can directly process non-SMS blocks without de-ciphering operations, significantly reducing processing time while maintaining security for SMS messages.
Data Source
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Figure 2
Figure 3A
AI summary
In an exemplary embodiment content of a data message to be sent on a control channel is determined, and a selection is made between ciphering and not ciphering the data message based on the determined content. By example if from the content it is determined that that the data message is a SMS message, ciphering is selected and the control channel is a SACCH; else ciphering is not selected. Such a determination may be made by checking a service access point identifier for a data block comprising the data message. A data message within a data block received on the control channel is determined to be ciphered or not ciphered using only information within the data block, and the received data message is processed according to the determination. In another embodiment the FACCH is selected for sending the message if it is a SMS, and ciphering is selected for all data blocks sent on the FACCH.