Inherent vulnerabilities in hybrid CDMA & cryptographic spread spectrum for space systems

Conference item

Direct Sequence Spread Spectrum (DSSS) is used to simplify frequency management for constellations and for use of data relay satellites, to improve satellite mission availability against unintentional interference and protect space RF links against jamming, eavesdropping, and spoofing. Whilst current standards focus on cooperative Code Division Multiple Access (CDMA) DSSS methods, high-value government and military assets increasingly use cryptographic DSSS to improve security. Including cryptographic DSSS into future revisions of the ETSI standard is currently considered an option, but it has been found that cryptographic DSSS is significantly worse at multiple access than the currently standardized methods. In this context, the European Space Agency and Thales Alenia Space have studied a hybrid CDMA/cryptographic DSSS construction designed to simultaneously provide multiple-access and security.

In this paper we perform the first systematic analysis of the hybrid protocol and discover a number of major design flaws which are fundamental to the design and seriously degrade the security of the system. In particular, we find that reuse of the cryptographic spreading sequence leads to a catastrophic failure wherein all satellites’ data sequences can be recovered with high probability given knowledge of any single satellite’s data sequence. This also enables sufficient recovery of the spreading sequence to spoof arbitrary messages, and increases vulnerability to optimized jamming. We evaluate and validate these findings through simulations with respect to real-world systems, and use this to propose countermeasures and system improvements which should be considered as standardization work continues.

Authors: Salkield, E; Köhler, S; Birnbach, S; Martinovic, I

• Publication status: Published
• Peer review status: Peer reviewed
• Publisher: European Space Agency
• Publication date: 2025-11-07
• Acceptance date: 2025-11-02
• Event title: Security for Space Systems (3S 2025)
• Event location: Noordwijk, Netherlands
• Event website: https://security4space.esa.int/2025
• Event start date: 2025-11-04
• Event end date: 2025-11-06
• Language: English
• Keywords: spread spectrum; security analysis; physicallayer security