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Galileo's Proposed Authentication Algorithm: Part 1 - Bert Hubert's writings
a day ago
- GNSS authentication is needed to prevent PVT spoofing, as current systems broadcast unauthenticated data.
- Galileo's OSNMA uses the TESLA protocol for efficient message authentication with limited bandwidth (40 bits per message).
- Symmetric signatures are used with delayed key disclosure; keys are generated in a chain so each key derives previous ones.
- Occasional public key signatures provide a trust anchor, allowing verification of the entire key chain.
- Receivers must not use disclosed keys to verify future messages; time synchronization is critical to prevent attacks.
Galileo's Proposed Authentication Algorithm: Part 2 - Bert Hubert's writings
a day ago
- Galileo's OSNMA uses a hierarchical message structure: pages (40 bits for OSNMA: 8 HKROOT, 32 MACK), 15 pages per subframe, 24 subframes per frame.
- The HKROOT field carries the Digital Signature Message (DSM), which includes a signed root key and configuration parameters, transmitted over multiple subframes.
- The MACK field contains MAC signatures and keys, but not for the page it's in; it signs bundles of data from the transmitting satellite and others, including GPS and BeiDou.
- Key verification follows TESLA: keys are disclosed later, and receivers derive the key's position in the chain using timestamps and subframe rate, then verify against the signed root key from the DSM.
- OSNMA is complicated by constraints: simple satellite hardware (bent-pipe), limited ground uplink capacity, and the need to authenticate out-of-reach satellites and other GNSS systems.
- MACK blocks are per subframe (1-3 blocks per subframe), each containing MACs and a key; the key ID is computed from the timestamp and the number of blocks per subframe.
GNSS Jamming and Spoofing, aka Galileo's Authentication Algorithm Part 3 - Bert Hubert's writings
a day ago
- GNSS jamming is a denial-of-service attack that stops positioning, but spoofing is more dangerous as it can deceive receivers into believing false locations.
- Spoofing detection is critical; turning spoofing into jamming makes it easier to handle, while undetected spoofing can lead to catastrophic outcomes.
- Meaconing involves recording and replaying authentic GNSS signals from one location to another, making it hard to detect without additional checks like precise clocks or multiple receivers.
- Receivers can use multiple techniques to detect spoofing, including monitoring signal strength, cross-checking satellite data from multiple constellations, and using RAIM (Receiver Autonomous Integrity Monitoring).
- OSNMA adds digital signatures to navigation messages to authenticate content, but it cannot fully protect against timing-based attacks or meaconing without precise time references.
- Advanced spoofing attacks may require multiple transmitters to mimic satellite parallax, raising the bar significantly for attackers.
- Receiver manufacturers often do not implement robust spoofing detection features, leaving commodity devices vulnerable to simple attacks.
- OSNMA is a valuable tool but not a complete solution; it works best alongside physical and software-based detection methods to raise the difficulty of successful attacks.

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osnma

Galileo's Proposed Authentication Algorithm: Part 1 - Bert Hubert's writings

Galileo's Proposed Authentication Algorithm: Part 2 - Bert Hubert's writings

GNSS Jamming and Spoofing, aka Galileo's Authentication Algorithm Part 3 - Bert Hubert's writings