Signalling Burst Interleaving for GSM Known-Plaintext Attack Prevention
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Solution Overview
Problem
Existing communication networks, such as GSM, are vulnerable to known-plaintext attacks that can crack encryption algorithms like A5/1, compromising security by allowing attackers to retrieve secret keys and session keys.
Innovation Solution
The method involves obtaining and encoding uncoded signalling messages, then interleaving predictable and unpredictable data before ciphering and transmitting bursts, specifically using block diagonal interleaving to mix data from multiple messages, thereby enhancing security without altering network architecture.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If data encryption is used in communication networks, then security is improved, but vulnerability to known-plaintext attacks increases because certain messages are known to attackers
Solution Approach 1:
The encoded signalling messages are divided into multiple bursts through interleaving, where each burst contains data from multiple different encoded signalling messages. This segmentation prevents attackers from obtaining complete plaintext samples for effective known-plaintext attacks, as the plaintext is distributed across multiple encrypted bursts.
Solution Approach 2:
Multiple encoded signalling messages are combined and interleaved together to form bursts. Each burst contains data from more than one encoded signalling message, making it difficult for attackers to correlate ciphertext with specific plaintext samples and thereby enhancing security against known-plaintext attacks.
2Reliability
If encryption algorithms like A5/1 are used, then communication privacy is provided, but the algorithms can be cracked with known-plaintext attacks allowing retrieval of secret keys
Solution Approach 1:
The signalling messages are encoded and interleaved into bursts before encryption. This preliminary processing of the plaintext ensures that even if attackers obtain encrypted bursts, they cannot easily derive the plaintext structure needed for effective known-plaintext attacks on the encryption algorithm.
Solution Approach 2:
The interleaving process acts as an intermediary between the plaintext messages and the encryption algorithm. By distributing plaintext from multiple messages across multiple bursts, the intermediary layer prevents direct correlation between plaintext and ciphertext, thereby protecting the encryption algorithm from known-plaintext attacks.
3Ease of operation
If signalling messages are transmitted between communication devices, then communication setup is enabled, but security is compromised because attackers can obtain plaintext samples
Solution Approach 1:
The signalling messages transmitted during communication setup are segmented and distributed across multiple bursts through interleaving. This segmentation ensures that even if attackers intercept multiple bursts, they cannot easily reconstruct complete plaintext samples needed for effective known-plaintext attacks.
Solution Approach 2:
The interleaving process creates a periodic distribution pattern where data from different signalling messages is systematically distributed across bursts. This periodic structure enhances security by making it difficult for attackers to predict or reconstruct plaintext from intercepted bursts, while still enabling proper communication setup.
Data Source
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AI summary
The present invention relates to a method of transmitting signalling information between a first communication network element, such as a base station controller, and a second communication network element, such as a mobile phone, in a communication network. The method can be implemented in the first communication network element. First, at least two uncoded signalling messages are obtained. These at least two uncoded signalling messages are then encoded to obtain at least two encoded signalling messages. Next the encoded signalling messages are divided into bursts by interleaving data from more than one encoded signalling message. Finally the bursts are transmitted to the second communication network element. At least some bursts contain data from a predictable signalling message and an unpredictable signalling message.