Navipedia - User contributions [en]

Galileo Open Service Navigation Message Authentication

2026-10-03T17:30:06Z

Ignacio.Fernandez: Major update (EC(IFH & TW))

{{Article Infobox2
|Category=GALILEO
|Editors=GMV, European Commission
|Level=Basic
|YearOfPublication=2026
|Title={{PAGENAME}}
}}

OSNMA (Open Service Navigation Message Authentication) is Galileo’s navigation message [[GNSS Authentication and encryption|authentication]] service. It is provided worldwide and free of charge. Its purpose is to give receivers the assurance that the received navigation data (ephemerides, clocks, satellite status, timing and other parameters) originates from the Galileo system itself and has not been modified, thereby increasing the ability to detect spoofing attacks.

The Galileo OSNMA concept design took place between 2013 and 2015, followed by its formal introduction into the Galileo legal basis and service baseline<ref>[https://eur-lex.europa.eu/legal-content/EN/TXT/PDF/?uri=CELEX:32017D0224 Commission Implementing Decision (EU) 2017/224]</ref><ref>[https://doi.org/10.1002/navi.125 Fernandez-Hernandez, I., et al. (2016). A Navigation Message Authentication Proposal for the Galileo Open Service. J. Inst. Navig., 63(1), pp. 85–102]</ref>. Following the development phase, the OSNMA Internal Testing phase started in October 2020<ref>[https://www.euspa.europa.eu/newsroom-events/news-archive/tests-galileo-osnma-underway Tests of Galileo OSNMA underway]</ref>. The OSNMA Public Observation Phase began in November 2021<ref>[https://www.gsc-europa.eu/news/euspa-launches-the-osnma-public-observation-test-phase EUSPA launches the OSNMA Public Observation Test Phase]</ref>, and finally the Initial Service was declared Operational on 24 July 2025, becoming the first authentication service offered by a GNSS<ref>[https://insidegnss.com/galileo-leads-the-way-in-gnss-spoofing-protection-with-osnma/ Galileo Leads the Way in GNSS Spoofing Protection with OSNMA]</ref>.

==Introduction to Galileo OSNMA==

Galileo OSNMA provides authentication of the Open Service navigation message transmitted in the E1 band. It uses a 40-bit field of the Galileo E1-B data message (I/NAV), previously unused, and therefore backward compatible with older versions of the Galileo OS Signal-in-Space ICD<ref>[https://www.gsc-europa.eu/sites/default/files/sites/all/files/Galileo_OS_SIS_ICD_in_force.pdf Galileo Open Service Signal-in-Space Interface Control Document]</ref>. OSNMA transmits Message Authentication Codes (MACs) authenticating the navigation data and the related keys with a delayed disclosure of more than 30 seconds. The current OSNMA field is composed of two parts<ref name="OSNMA_SISICD">[https://www.gsc-europa.eu/sites/default/files/sites/all/files/Galileo-OSNMA-SIS-ICD_in_force.pdf Galileo Open Service Navigation Message Authentication Signal-in-Space Interface Control Document]</ref>:
*The Header and Root Key (HKROOT) section (first 8 bits) includes the global headers and the Digital Signature Message (DSM), with information to authenticate the TESLA Root Key and other cryptographic material.
*The MAC and Key (MACK) section (next 32 bits) contains the Message Authentication Codes (MACs) and associated keys.

[[File:Galileo_OS_NMA_SIS.png|500px|OSNMA field in I/NAV word<ref name="OSNMA_SISICD"/>|centre|thumb]]

==Galileo OSNMA cryptographic functions and protocols==

The Galileo OSNMA protocol is based on existing cryptographic standards adapted to GNSS. Its core is based on lightweight cryptography standards<ref>[https://www.iso.org/obp/ui/en/#iso:std:iso-iec:29192:-7:ed-1:v1:en Information security - Lightweight cryptography - Part 7: Broadcast authentication protocols, ISO/IEC Standard 29192-7]</ref>, in particular an adaptation of the Timed Efficient Stream Loss-Tolerant Authentication (TESLA) protocol<ref>[https://doi.org/10.1109/SECPRI.2000.848446 Perrig, A., et al. (2000). Efficient authentication and signing of multicast streams over lossy channels. Proc. 2000 IEEE Symposium on Security and Privacy, pp. 56-73]</ref>. TESLA is particularly suitable for OSNMA because it requires relatively low bandwidth for authentication data and is robust to data loss. However, as a delayed-key-disclosure protocol, it requires the receiver to have a sufficiently accurate time estimate before processing OSNMA data<ref name="OSNMA_RXGL">[https://www.gsc-europa.eu/sites/default/files/sites/all/files/Galileo-OSNMA-RX-Guidelines_in_force.pdf Galileo Open Service Navigation Message Authentication Receiver Guidelines ]</ref>.

The TESLA implementation used for Galileo OSNMA has two main optimizations with respect to the standard protocol. Firstly, it uses a single key chain for all the satellites, so users will be able to receive the key by any satellite in view. Secondly, satellites transmitting OSNMA can “cross-authenticate” other satellites.

TESLA uses a one-way chain of cryptographic keys generated by repeatedly applying a one-way function based on a cryptographic hash. The one-way property makes it computationally infeasible to derive future undisclosed keys from already disclosed keys. But a receiver can verify a newly disclosed key against an earlier authenticated element of the chain. This implies that the receiver must have a previously disclosed key (such as the Root Key) certified as correct.

The TESLA Root Key is authenticated through an ECDSA digital signature using an OSNMA Public Key available to the receiver. Public Keys transmitted through the Signal-in-Space can in turn be authenticated using the OSNMA Merkle Tree, whose root acts as a trust anchor, as per the Galileo OSNMA Signal-In-Space ICD<ref name="OSNMA_SISICD"/>. The required cryptographic material, including Public Keys, Merkle Tree data and associated certificates, is also distributed through the OSNMA Internet Data Distribution (IDD) interface<ref>[https://www.gsc-europa.eu/sites/default/files/sites/all/files/Galileo-OSNMA-IDD-ICD_in_force.pdf Galileo Open Service Navigation Message Authentication Internet Data Distribution Interface Control Document]</ref>.

==Authentication based on Galileo OSNMA==

The way in which authentication based on Galileo OSNMA works can be summarized as follows:
*The receiver demodulates the navigation data and the Message Authentication Code (MAC) that will authenticate the navigation data.
*The receiver demodulates the key required to authenticate the MAC. This key is broadcast by the system with a predefined delay with respect to the associated MAC.
*The receiver authenticates the key with a previous key from the chain that is considered authentic, or from the Root Key. As explained before, this key is part of a pre-generated one-way chain whose root is public, and which is transmitted in reverse order with respect to its generation.
*The receiver locally re-computes the MAC with the navigation data and the key, which should match the previously received MAC. If this is the case, the navigation data can be considered as authentic.

The Galileo programme recommends to implement OSNMA in receivers in combination with other anti-spoofing measures. Also, the partial unpredictability of the OSNMA bits can be exploited by suitably designed receivers to provide an additional level of protection at signal/ranging level against certain replay and spoofing attacks<ref name="OSNMA_RXGL"/>.

==Galileo OSNMA architecture==

A summary of the Galileo OSNMA architecture is shown below. In order to fit Galileo OSNMA into the Galileo infrastructure within schedule and cost, the OSNMA module was developed as part of the European GNSS Service Centre, located in Torrejón de Ardoz.

[[File:Galileo_OS_NMA_Architecture.png|700px|Galileo OSNMA Architecture<ref>[https://www.euspa.europa.eu/sites/default/files/expo/2.4_moises_navarro-gallardo_-_airbus_-_guidelines_os_nma_implementation_in_smartphones.pdf Navarro-Gallardo, M. (2019). Guidelines: OS-NMA implementation in smartphones]</ref>|centre|thumb]]

==Galileo OSNMA adoption and prospects==

During the OSNMA public observation phase (2021-2025), Galileo OSNMA started to be integrated by major receiver manufacturers. This was accelerated at the OSNMA official launch in July 2025<ref>[https://www.u-blox.com/en/technologies/osnma-galileo-spoofing U-blox (2025). Galileo OSNMA; The new message authentication feature]</ref><ref>[https://www.septentrio.com/en/learn-more/insights/osnma-latest-gnss-anti-spoofing-security Septentrio (2025). OSNMA: the latest in GNSS anti-spoofing security]</ref>. Since then, a growing number of GNSS receivers incorporate OSNMA as part of their anti-spoofing solutions for applications including road transport, timing and synchronisation, surveying, autonomous systems and other professional markets. EUSPA maintains a non-exhaustive list of receivers including OSNMA as part of their list of Galileo compatible devices<ref>[https://www.gsc-europa.eu/support-to-developers/galileo-compatible-devices/receivers-implementing-galileo-osnma Receivers implementing Galileo OSNMA]</ref>. OSNMA is also being incorporated as part of the next generation standards for civil aviation by the ICAO (International Civil Aviation Organization), envisaged to become applicable by 2028.

The Smart Tachograph is a special case of early OSNMA adoption<ref>[https://transport.ec.europa.eu/transport-modes/road/tachograph_en Tachograph - Mobility and Transport - European Commission]</ref>. The latest Smart Tachograph Regulations required the implementation of OSNMA as part of its technical specification. Thanks to that, since December 2025, all new heavy vehicles in Europe of more than 3.5 tonnes, like trucks and buses, carry OSNMA.

Galileo OSNMA is the world’s first civil GNSS authentication service, but other satellite navigation systems such as QZSS or GPS have since incorporated or are studying the incorporation of authentication to their signals. Galileo is also testing its new [[Galileo Signal Authentication Service|Signal Authentication Service]] and will improve its overall authentication capabilities as part of its 2<sup>nd</sup> Generation.

==Credits and further information==

This article has been created based on Galileo OSNMA specifications and other information as indicated through references. Further information about OSNMA can be found on the European GNSS Service Centre website<ref>[https://www.gsc-europa.eu/galileo/services/galileo-open-service-navigation-message-authentication-osnma Galileo Open Service Navigation Message Authentication (OSNMA)]</ref>. EUSPA also publishes regularly performance reports with the Galileo OSNMA performance in the last quarter<ref>[https://www.gsc-europa.eu/electronic-library/performance-reports/galileo-open-service-navigation-message-authentication-osnma Galileo Open Service Navigation Message Authentication (OSNMA) Quarterly Performance Reports]</ref>. Finally, OSNMA open source packages such as OSNMAlib facilitate implementation of the OSNMA protocol and provide some real-time monitoring capability<ref>[https://osnmalib.eu/ OSNMAlib]</ref>.

==References==
<references/>

[[Category:GALILEO|!]]

Galileo High Accuracy Service (HAS)

2026-09-17T15:21:40Z

Ignacio.Fernandez: Major update

{{Article Infobox2
|Category=GALILEO
|Editors=European Commission
|Level=Basic
|YearOfPublication=2026
|Title={{PAGENAME}}
}}

The [[GALILEO General Introduction|GALILEO]] System is an independent, global, European-controlled, satellite-based navigation system and provides a number of services to users equipped with Galileo-compatible receivers.

The GALILEO High Accuracy Service (HAS) provides free of charge high-accuracy PPP corrections, in the Galileo E6-B data component and by terrestrial means, for Galileo and GPS (single and multi-frequency) to achieve real-time improved user positioning performances (positioning error of less than two decimetres in nominal conditions).

The Galileo High Accuracy Service resulted from the re-scoping of the former Galileo Commercial Service (CS). The Galileo HAS Initial Service (Phase 1) was declared operational in January 2023. Further evolutions are being developed in HAS Phase 2.

==Target Applications==

[[File:Galileo 02 wp02.jpg|250px|Galileo HAS Civil Application|right|thumb]]

The High Accuracy Service (HAS) is aimed at applications requiring higher performance than that offered by the Open Service.<ref>[https://www.gsc-europa.eu/galileo/services Galileo Services on GSC website]</ref><ref>[https://www.gsc-europa.eu/galileo/services/galileo-high-accuracy-service-has Galileo HAS on GSC website]</ref> It is provided on a free of charge basis, with content and format of data publicly and openly available on a global scale. Developing applications using the HAS signals opens a wide range of possibilities. The worldwide coverage brings a strong advantage for applications requiring global availability, even in areas with limited wireless communications coverage.

Applications of Galileo HAS span a wide range of land, sea, and air domains. They include high‑precision GIS and mapping, cadastral and hydrographic surveying. Galileo HAS can also support advanced mobility and automation, powering applications such as automated driving, machinery guidance and autonomous surface vessel navigation. Other applications are robotics, port operations, and even smartphone‑based mapping and navigation support for visually impaired users, demonstrating the service’s versatility across professional and societal needs.

==Precise Point Positioning==

Multiple approaches have been developed to provide positioning accuracy at the decimetre level or better: real time kinematic (RTK), precise point positioning (PPP), and more recently PPP-RTK. The main advantage of using PPP instead of RTK is that it provides a global and absolute positioning and timing service without the need for nearby reference stations. PPP is based on the derivation of accurate GNSS satellite orbits and clock data as well as biases (i.e. code and phase biases) using a sparse, globally distributed network of reference stations. Receivers apply this data to estimate a user position based on carrier phase measurements. The ionospheric delays are typically estimated by the PPP receiver or removed by performing the ionosphere-free combination. However, atmospheric data may be supplied to reduce the convergence time and to improve the accuracy for single-frequency users. In Galileo HAS, PPP data is distributed through the Galileo system itself.

==Galileo HAS Data==

Galileo HAS data are transmitted using the data (E6-B) component in the E6 band. E6 signals are modulated using binary phase shift keying BPSK(5) at a carrier frequency of 1278.75 MHz, which is used by all satellites and shared through a code division multiple access (CDMA) RF channel access method.<ref name="HAS_SDD">[https://www.gsc-europa.eu/electronic-library/programme-reference-documents/galileo-in-force/has Galileo HAS Service Definition Document]</ref> Therefore, the signal main lobe and most of the signal power is in the 1273.75-1283.75 MHz band. The HAS data are transmitted within the C/NAV navigation message in the E6-B signal component at a rate of 448 bps.<ref name="HAS_SISICD">[https://www.gsc-europa.eu/electronic-library/programme-reference-documents/galileo-in-force/has Galileo HAS Signal-in-Space Interface Control Document]</ref>

The Galileo E6-B channel is well suited to transmit PPP information. The available rate of 448 bps per satellite allows the transmission of PPP data at an adequate update rate to provide accuracy at the centimetre level.<ref name="HAS_SISICD"/> The HAS message also uses a specific outer-layer coding technique developed for optimally transmitting long messages from satellite constellations, called HPVRS (High Parity Vertical Reed-Solomon). The Galileo HAS corrections are also available through a terrestrial link as an addition dissemination channel.<ref>[https://www.gsc-europa.eu/electronic-library/programme-reference-documents/galileo-in-force/has Galileo HAS Internet Data Distribution Interface Control Document]</ref>

High accuracy corrections follow a similar format to Compact-State Space Representation (CSSR). Note that the High Accuracy Service does not offer integrity information.

[[File:Galileo_Signals.png|250px|Galileo Signal Frequencies|centre|thumb]]

==Galileo HAS Service Levels==

The HAS comprises two services levels:<ref name="HAS_SDD"/>
*Service Level 1 (SL1) with global coverage, providing high accuracy corrections (orbits, clocks) and biases (code and phase) for Galileo E1/E5b/E5a/E6 and E5AltBOC and GPS L1/L5/L2 signals.
*Service Level 2 (SL2) with regional coverage, providing SL1 corrections plus ionospheric corrections.

The next table summarizes the main characteristics for each of the Galileo HAS Service levels:

{| class="wikitable" align="center"
|+align="bottom" |''Table 1- Main HAS characteristics and target performances<ref name="HAS_note">[https://www.gsc-europa.eu/sites/default/files/sites/all/files/Galileo_HAS_Info_Note.pdf Galileo HAS Info Note]</ref>''
|-
! HAS
! Service Level 1
! Service Level 2
|- align="center"
| COVERAGE
| Global
| European Coverage Area (ECA)
|- align="center"
| TYPE OF CORRECTIONS
| PPP - orbit, clock, biases (code and phase)
| PPP - orbit, clock, biases (code and phase) incl. atmospheric corrections
|- align="center"
| FORMAT OF CORRECTIONS
| Open format similar to Compact-SSR (CSSR)
| Open format similar to Compact-SSR (CSSR), plus Galileo HAS ionospheric correction message
|- align="center"
| DISSEMINATION OF CORRECTIONS
| Galileo E6-B using 448 bits per satellite per second / terrestrial (internet)
| Galileo E6-B using 448 bits per satellite per second / terrestrial (internet)
|- align="center"
| SUPPORTED CONSTELLATIONS
| Galileo, GPS
| Galileo, GPS
|- align="center"
| SUPPORTED FREQUENCIES
| E1/E5a/E5b/E6/E5 (AltBOC), L1/L5/L2C
| E1/E5a/E5b/E6/E5 (AltBOC), L1/L5/L2C
|- align="center"
| HORIZONTAL ACCURACY 95%
| < 20 cm
| < 20 cm
|- align="center"
| VERTICAL ACCURACY 95%
| < 40 cm
| < 40 cm
|- align="center"
| CONVERGENCE TIME
| < 300 s
| < 100 s
|- align="center"
| AVAILABILITY
| 99%
| 99%
|- align="center"
| USER HELPDESK
| 24/7
| 24/7
|}

The HAS Initial Service is currently providing Service Level 1 with reduced coverage and performance compared to the Full Service. The Minimum Performance Levels (MPLs) are defined in the Galileo HAS Service Definition Document.<ref name="HAS_SDD"/> Performance reports are published on a quarterly basis.<ref>[https://www.gsc-europa.eu/electronic-library/performance-reports/galileo-high-accuracy-service-has Galileo HAS Performance Reports]</ref>

==System Level Implementation==

===Galileo HAS High Level Architecture===

The Galileo system elements involved in the provision of the Galileo High Accuracy Service are:<ref name="HAS_note"/>
*High Accuracy Data Generator (HADG), located at the GSC (European GNSS Service Centre), receives data from the Galileo Sensor Stations (GSS) and generates corrections for Galileo and GPS. Note that additional reference station networks of Galileo Experimental Sensor Stations (GESS), from the Galileo System Test Bed, and RIMS from EGNOS, will be incorporated in Phase 2.
*The High Accuracy (HA) corrections are sent in real time to the Galileo core infrastructure.
*The Galileo core infrastructure receives the HA data and compiles the information in one single message of 448 bits per second and per connected satellite.
*The Galileo core infrastructure uploads the HA data to the Galileo satellites through the Uplink Stations (ULS).
*Galileo satellites broadcast HA data through the Galileo E6-B signal component.
*HA data is also provided through the terrestrial link, accessible to the users through the Internet.
*Users receive the HA data and implement PPP algorithms to apply HA corrections to the Galileo and GPS navigation data.

[[File:Architecture_HAS_v2.png|550px|HAS High Level Architecture<ref name="HAS_note"/>|centre|thumb]]

===Galileo HAS Roadmap===

The Galileo High Accuracy Service is implemented in a stepped approach:<ref name="HAS_note"/>
*Phase 0 (HA testing and experimentation) focused on activities aimed at validating Galileo’s dissemination capabilities through the E6-B channel and performing initial high-accuracy testing. Internal testing started in 2019. HAS SiS tests were executed from Q1 2021.
*Phase 1 (HA Initial Service). Provision of an initial Galileo High Accuracy Service resulting from the implementation of a high-accuracy data generation system processing Galileo system data only. The HA initial service is available since 24/01/2023 and delivers Service Level 1 performance.<ref>[https://doi.org/10.1007/s10291-022-01247-x Fernandez-Hernandez, I., et al., Galileo High Accuracy Service: initial definition and performance. GPS solutions, 26(3), 65.]</ref><ref>[https://doi.org/10.1007/s10291-023-01410-y Naciri, N., Yi, D., Bisnath, S., de Blas, F. J., & Capua, R. (2023). Assessment of Galileo High Accuracy Service (HAS) test signals and preliminary positioning performance. GPS solutions, 27(2), 73.]</ref>
*Phase 2 (HA Full Service). Full provision of the Galileo High Accuracy Service, including Service Level 1 and Service Level 2, fulfilling its target performance. In Phase 2, additional stations are added to improve performance and the HAS data will also support additional features such as the authentication of the HAS data.
*Phase X (HA Evolution). Implementation of HAS Evolutions in the frame of Galileo 2<sup>nd</sup> generation developments, addressing the HAS users’ feedback and lessons learned from the previous phases.

[[File:Roadmap_HAS_v2.png|550px|Galileo HAS Roadmap<ref name="HAS_note"/>|centre|thumb]]

==Galileo HAS Adoption==

Following its Initial Service Declaration in January 2023, the High Accuracy Service started to be integrated by major high-precision receiver manufacturers. A growing number of GNSS receivers now incorporate HAS as part of their precise point positioning (PPP) solutions for applications including precision agriculture, transportation, autonomous systems and other professional markets. EUSPA maintains a non-exhaustive list of receivers supporting HAS as part of their list of Galileo compatible devices.<ref>[https://www.gsc-europa.eu/support-to-developers/galileo-compatible-devices/receivers-implementing-galileo-has Receivers implementing Galileo HAS]</ref>

==Credits==

The information of this article has been compiled based on public information from the Galileo HAS Info Note and other sources as indicated through the references. The initial (2011) version of this article was edited by GMV.

==References==
<references/>

[[Category:GALILEO|Commercial]]
[[Category:GALILEO Services|Commercial]]

File:Roadmap HAS v2.png

2026-09-17T08:41:14Z

Ignacio.Fernandez: Galileo HAS Roadmap

== Summary ==
Galileo HAS Roadmap

File:Architecture HAS v2.png

2026-09-17T08:40:06Z

Ignacio.Fernandez: HAS High Level Architecture

== Summary ==
HAS High Level Architecture

Galileo General Introduction

2026-09-16T12:38:19Z

Ignacio.Fernandez: Added link to the Galileo Signal Authentication Service page

{{Article Infobox2
|Category=GALILEO
|Editors=GMV
|Level=Basic
|YearOfPublication=2025
|Logo=GMV
|Title={{PAGENAME}}
}}
Galileo is Europe’s own global navigation satellite system, providing a highly accurate, guaranteed global positioning service under civilian control. It is inter-operable with others GNSS such as [[GPS General Introduction|GPS]], [[GLONASS General Introduction|GLONASS]] and [[BeiDou General Introduction|BEIDOU]]. Galileo receivers compute their position in the [[GALILEO Reference Frame|Galileo Reference System]] using satellite technology and based on [[An intuitive approach to the GNSS positioning|trilateration principles]].

The Galileo system started its initial services on December 15th, 2016, <ref>[http://europa.eu/rapid/press-release_IP-16-4366_en.htm Galileo goes live!]</ref> and continues to evolve with infrastructure deployment towards Full Operational Capability (FOC).

Galileo system is in constant improvement, leading to a [https://www.esa.int/Applications/Satellite_navigation/Galileo_Second_Generation_enters_full_development_phase Galileo Second Generation (G2)] satellites which will revolutionize the Galileo fleet. G2 satellites are much larger, with significant changes with respect to the first version like the use of electric propulsion, an enhanced antenna with larger radiation area, inter-satellite links between the satellites which will reduce their dependency on the availability of ground installations and the addition of two atomic clocks. Moreover, G2’s fully digital payloads are being designed to be easily reconfigured in orbit, enabling them to actively respond to the evolving needs of users with novel signals and services.<ref>[https://www.esa.int/ESA_Multimedia/Images/2021/05/Galileo_Second_Generation Galileo Second Generation]</ref>

==Introduction==

[[File:Galileo_Art.png‎‎|400px|Galileo Constellation (artistic interpretation)|left|thumb]] Galileo is Europe's Global Navigation Satellite System (GNSS), offering highly accurate, civilian-controlled positioning, navigation, and timing services. Galileo is designed to be fully interoperable with GPS, GLONASS, and BeiDou, providing enhanced reliability and precision. The system operates with a constellation of satellites in Medium Earth Orbit (MEO) at an altitude of 23,222 km, ensuring continuous global coverage. From most locations, six to eight satellites will always be visible <ref>[https://www.euspa.europa.eu/eu-space-programme/galileo/faqs/how-many-satellites-will-galileo-have EUSPA FAQs]</ref>, reaching high values of availability even under challenging conditions. Moreover, Galileo signals are transmitted in four frequency bands (E5a, E5b, E6 and E1), enabling single and dual frequency positioning for users equipped with suitable receivers allowing positions and timing to be determined very accurately to within a few centimetres. As of 2025, Galileo provides positioning accuracy up to 20 cm horizontally and 40 cm vertically.<ref>[https://www.esa.int/Applications/Satellite_navigation/New_Galileo_service_set_to_deliver_20_cm_accuracy ESA, Applications, Satellite Navigation]</ref>

Satellite navigation has become deeply integrated into everyday life, supporting industries and activities that we often take for granted. From personal and transport navigation to precision operations such as autonomous vehicles, GNSS is a critical service. However, the consequences of losing access to these signals would be severe. Truck and taxi drivers, airline crews, and maritime vessels would be unable to navigate effectively. Additionally, financial transactions, telecommunications, and emergency services would be significantly impacted, leading to chaos in public and private sectors. To mitigate such risks, Galileo ensures that satellite navigation remains under civilian authority, giving Europe greater autonomy and control over its satellite-based services. Providing a robust GNSS solution upon the potential unavailability of other GNSS systems.

With the launch and ongoing expansion of Galileo, these risks are greatly reduced. By diversifying the sources of GNSS signals, Galileo offers users a more resilient and reliable navigation service. In addition, its civilian control ensures transparency and accountability, enhancing public trust. Beyond improving basic navigation services, Galileo’s advanced capabilities also support precise timing and synchronization, which are essential for critical sectors such as banking, telecommunications, and scientific research.

The combination of Galileo and [[GPS General Introduction|GPS]] signals ([[Principles of Interoperability among GNSS| GNSS Inter-Operability]]) in dual receivers opens the door to new [[GNSS Applications|GNSS applications]] that require a higher level of precision than currently available with [[GPS General Introduction|GPS]] alone. Examples of these applications are: increase the success rate of rescue operations in the mountains, monitoring of the distribution and dilution of chemicals for agriculture interests, etc.<ref name="EUSPA News archive">[https://www.euspa.europa.eu/newsroom-events/news-archive/galileo-european-satellite-navigation-system-opens-business-opportunities-and-makes-life-easiery EUSPA News archive]</ref>

In addition, Galileo enhances the overall availability and coverage of GNSS signals. For instance, its large constellation of satellites improves signal accessibility in densely populated urban areas, where tall buildings can obstruct signals from satellites low on the horizon.<ref name="European Commission Galileo System">[https://defence-industry-space.ec.europa.eu/eu-space/galileo-satellite-navigation/galileo-system_en European Commission Galileo System]</ref>

With Galileo, Europe is able to exploit the opportunities provided by satellite navigation to the full extent. [[GNSS Receivers General Introduction|GNSS Receivers]] and equipment manufacturers, application providers and service operators benefit from novel business opportunities.<ref name="EUSPA News archive" /><ref name="European Commission Galileo System" />

==History and Development==

As early as the 1990s, the [[Wikipedia:European Union|European Union]] saw the need for Europe to have its own global satellite navigation system.<ref>[https://eur-lex.europa.eu/LexUriServ/LexUriServ.do?uri=OJ:C:1999:221:0001:0003:EN:PDF Council Resolution of 19 July 1999 on the involvement of Europe in a new generation of satellite navigation services -Galileo- Definition phase]</ref>The conclusion to build one was taken in similar spirit to other decisions made in the 1970s to embark on other well-known European endeavours, such as the [https://www.esa.int/Enabling_Support/Space_Transportation/Launch_vehicles/Europe_s_launchers Ariane] launcher and the formation of the Airbus Industrie GIE consortium. The [[Wikipedia:European Union|European Union]] and [https://www.esa.int/ European Space Agency] joined forces to build Galileo, an independent European system under civilian control.

The definition phase and the development and In-Orbit Validation phase of the Galileo program were carried out by the [https://www.esa.int/ European Space Agency] and co-funded by ESA and the [[Wikipedia:European Union|European Union]]. The Full Operational Capability phase of the Galileo program is fully funded by the European Union and managed by the [[Wikipedia:European Commission|European Commission]]. The Commission and the European Space Agency signed a delegation agreement by which ESA acts as design and procurement agent on behalf of the Commission.

The Galileo program was structured according to three main phases<ref name="European Commission Galileo System" />: [[Galileo Future and Evolutions| In-Orbit Validation (IOV), Initial Operational Capability (IOC) and Full Operational Capability (FOC) phases]].

==GALILEO Services==

The Galileo mission and services were elaborated during the initial definition phase in consultation with user communities and the Member States. The high-performance services that the Galileo system offers for users worldwide are the followings:<ref name="Galileo services">[https://www.gsc-europa.eu/galileo/services Galileo services in European GNSS Service Centre portal]</ref>

*[[GALILEO Open Service|Open Service (OS)]]: The freely accessible Open Service targets the mass market and is intended for motor vehicle navigation and location-based mobile telephone services. Free to the user, it provides positioning and synchronization information intended for high-volume satellite radio navigation applications; Galileo Open Service will include in the short term an authentication mechanism through [[Galileo Open Service Navigation Message Authentication|Galileo OS-NMA]].

*[[Galileo High Accuracy Service (HAS)|High Accuracy Service (HAS)]]:The HAS is an open access and free of charge service based on the provision of precise corrections (orbit, clock, biases) transmitted in the Galileo E6 signal (E6-B, data component) as well as via the internet, allowing the user to achieve improved positioning performance. The HAS signal can be encrypted in order to control access to the Galileo HAS services.

*[[Galileo Public Regulated Service (PRS)|Public Regulated Service (PRS)]]: The Public Regulated Service is restricted to government-authorised users, for sensitive applications which require a high level of service continuity. It will be encrypted and designed to be more robust, with anti-jamming mechanisms and reliable problem detection. This service is intended for security and strategic infrastructure (e.g. energy, telecommunications and finance).

*[[Galileo Search and Rescue Service|Search and Rescue Service (SAR)]]: Galileo's worldwide search and rescue service will help to forward distress signals to a rescue coordination centre by detecting emergency signals transmitted by beacons and relaying messages to them.

Later, new services emerged and are currently under development with G2 satellites incorporation. These services are the followings:<ref name="Galileo services" />

*[[Galileo Open Service Navigation Message Authentication|Open Service navigation Message Authentication (OSNMA)]]: Free of charge supplementary service to the Galileo Open Service (OS), designed to enhance the reliability and security of the system. OSNMA ensures that the Galileo navigation messages received by users are authentic, confirming that they originate from the Galileo satellite constellation. By providing this layer of authentication, OSNMA helps protect against spoofing and signal manipulation, offering users greater confidence in the integrity of the data. This is especially crucial for applications requiring high precision and trust, such as aviation, maritime navigation, and critical infrastructure. OSNMA enhances the overall security of Galileo, aligning with Europe’s goal of offering secure and dependable GNSS services under civilian control. The incorporation of G2 satellites improves the robustness of this service, with advanced jamming and spoofing protection mechanisms to safeguard Galileo signals.

*[[Galileo Signal Authentication Service|Signal Authentication Service (SAS)]]: Service which enables an authenticated positioning service by complementing the OSNMA with E6-based ranging authentication capabilities targeting to support civil applications.

*'''Galileo Emergency Warning Satellite Service (EWSS)''': Service which allows national civil protection authorities to rapidly transmit alerts to smartphones (or any Galileo-enabled device) in any place of the globe for enhanced emergency response and resilient risk management. The alert service is independent of the mobile communication infrastructure, and remains operational even when existing systems have been destroyed or are not available (e.g. network saturation or poor mobile network coverage).

*'''Timing Service (TS)''': The Galileo OS offers free positioning and timing/synchronization data. Currently, its timing capabilities are limited to basic determination and dissemination. However, the Galileo Programme has identified the need to expand these features into dedicated, enhanced Timing Services in the Galileo Second Generation. This upgrade will focus on supporting Critical Infrastructure applications by providing features like the Timing service Level Monitoring (TSLM) which consists in monitoring the GST and UTC accuracy.

==GALILEO Architecture==

[[File:Galileo Space Segment.jpg|250px|Galileo Space Segment|right|thumb]]To ensure these Galileo services, a specific architecture is deployed. The Galileo system is divided into three major segments: [[GALILEO Space Segment|Space Segment]], [[GALILEO Ground Segment|Ground Segment]] and [[GALILEO User Segment|User Segment]]. For details see [[GALILEO Architecture|Galileo Architecture]].

The main functions of the [[GALILEO Space Segment|Galileo Space Segment]] are to generate and transmit code and carrier phase signals with a specific [[GALILEO Signal Plan|Galileo signal structure]], and to store and retransmit the navigation message sent by the [[GALILEO Ground Segment|Ground Segment]]. These transmissions are controlled by Passive Hydrogen Masers (PHMs) and Rubidium (RAFS) atomic clocks on board the satellites.

The Galileo satellite system nominal constellation uses a specific layout in space called a 24/3/1 Walker constellation. This means there are 24 main satellites orbiting the Earth at Medium Earth Orbit (MEO), divided into 3 equally spaced orbital planes and completing a full orbit around the Earth in 14 hours. These planes are tilted at 56 degrees from the Equator, allowing the satellites to cover most of the globe. The orbits are spaced 120 degrees apart, ensuring consistent global coverage.

In addition to the main satellites, extra (auxiliary) satellites can also be added. These don't follow the original layout and are placed in other available positions to support the system.

The Galileo constellation consists of over 30 satellites, the majority of which are operational and actively contributing to service provision, while a few may be temporarily unavailable.<ref>[https://www.gsc-europa.eu/system-service-status/constellation-information EUSPA, Constellation Information]</ref>

The [[GALILEO Ground Segment|Ground Segment]] (also referred to as Control Segment) is the responsible for the proper operation of the GNSS system. Its basic functions are:

*To control and maintain the status and configuration of the satellite constellation.
*To predict ephemeris and satellite clock evolution.
*To keep the corresponding GNSS time scale (through atomic clocks).
*To update the navigation messages for all the satellites.

The [[GALILEO Ground Segment|Ground Segment]] constitutes the major system element controlling the entire constellation, the navigation system facilities and the dissemination services. It is composed of two Galileo Control Centres (GCC), each composed of a Ground Control Segment (GCS) and a Ground Mission Segment (GMS).

In one hand, the GCS manages and monitors the satellites and their equipment, as well as planning and automating tasks to ensure everything operates safely and correct. It also supports operations related to the satellite payloads. On the other hand, the GMS determines the navigation and timing data part of the navigation messages.

A worldwide network of ground stations implementing monitoring and control functions are needed for the GCS and GMS. These are the Galileo Sensor Stations (GSS), the Telemetry, Tracking and Control stations (TT&C), and the Galileo Uplink Stations (ULS). The GSS provides Galileo SIS measurements and data to the GCCs. The Telemetry, Tracking and Control stations (TT&C) provide telemetry data and uplinks the control commands required to maintain the Galileo satellites. Finally, the Galileo Uplink Stations (ULS) distribute and uplink the mission data to the Galileo constellation.<ref>[https://www.gsc-europa.eu/galileo/system EUSPA, Galileo System]</ref>

The [[Galileo User Segment|Galileo User Segment]] is composed of [[Galileo Receivers|Galileo Receivers]]. Their main function is to receive Galileo signals, determine pseudoranges (and other observables), and solve the navigation equations to obtain their coordinates and provide a very accurate time.

==Galileo Signal Characteristics==

The Galileo navigation Signals are transmitted in the four frequency bands indicated in the next figure. These four frequency bands are the E5a, E5b, E6 and E1 bands. They provide a wide bandwidth for the transmission of the Galileo Signals.<ref name="Galileo OS Signal In Space ICD">[https://www.gsc-europa.eu/sites/default/files/sites/all/files/Galileo_OS_SIS_ICD_in_force.pdf Galileo OS Signal In Space ICD]</ref>

[[File:Galileo Frequency Plan.png|571px|Galileo Frequency Plan|none|thumb]]

The Galileo frequency bands have been selected in the allocated spectrum for Radio Navigation Satellite Services (RNSS). In addition to that, E5a, E5b and E1 bands are included in the allocated spectrum for Aeronautical Radio Navigation Services (ARNS), employed by Civil-Aviation users, and allowing dedicated safety-critical applications. The names of the Galileo signals are the same as the corresponding carrier frequencies. Note that E5a and E5b signals are part of the E5 bandwidth.<ref name="Galileo OS Signal In Space ICD" />

==GALILEO Performances==

The Galileo [[GNSS Performances|performances]] are different for each service.

For [[GALILEO Open Service|Open Service (OS)]], the positioning accuracy MPLs for SF and DF, and depending on the user location are:

<div style="text-align:center;">
{| class="wikitable" style="display:inline-table;"
|+ style="caption-side:bottom; color:black;"|''[https://www.gsc-europa.eu/sites/default/files/sites/all/files/Galileo-OS-SDD_v1.3.pdf Galileo OS Positioning Accuracy MPLs] at average and worst user location''
! rowspan="2" | GALILEO OS POSITIONING ACCURACY
! colspan="2" | HORIZONTAL ERROR
! colspan="2" | VERTICAL ERROR
|-
! SF
! DF
! SF
! DF
|-
| style="text-align:center;" | Average user location
| ≤ 5m (95%)
| ≤ 5m (95%)
| ≤ 8m (95%)
| ≤ 8m (95%)
|-
|style="text-align:center;" | Worst user location
| ≤ 10m (95%)
| ≤ 10m (95%)
| ≤ 16m (95%)
| ≤ 16m (95%)
|}
</div>

Currently, the [[GALILEO Open Service|Open Service (OS)]] meet these requirements and achieve values of around 1.5 and 2.5 meters (HPE and VPE, correspondingly) for dual frequency combinations (E1/E5a and E1/E5b).

The following figures are an example of the positioning performances achieved during January 2025 (E1/E5a and E1/E5b):

<center>
<gallery widths=350 heights=250>
File:HPE for Galileo E1E5a users in January 2025.png
File:HPE for Galileo 51E5b users in January 2025.png
</gallery>
'''''HPE statistics for Galileo users in January 2025.'''''
</center>
<center>
<gallery widths=350 heights=250>
File:VPE for Galileo E1E5a users in January 2025.png
File:VPE for Galileo E1E5b users in January 2025.png
</gallery>
'''''VPE statistics for Galileo users in January 2025.'''''
</center>

Refer to [https://www.gsc-europa.eu/electronic-library/performance-reports/galileo-open-service-os#:~:text=The%20Galileo%20Open%20Service%20(OS)%20Performance%20Reports%20are,applicable%20Galileo%20Open%20Service%20Service%20Definition%20Document%20(SDD). EUSPA, Galileo Open Service Performance Reports] for quarterly published performance reports of Galileo OS.

The characterisation of Galileo OS in terms of integrity and continuity is currently under development. However, the Probability of SIS Fault and the Probability of Constellation Fault are parameters which help in giving a cofinance at any instantaneous signal. The Probability of SIS Fault is defined as the probability that the instantaneous ranging signal error of a healthy Galileo satellite (excluding atmospheric and receiver errors) exceeds “k” times (being factor “k” the number of standard deviations from the mean corresponding to a probability of Psat in a normal distribution) the Galileo user range accuracy (Galileo URA). And the Probability of Constellation Fault is the probability that the instantaneous ranging signal error of two or more healthy Galileo satellites (also excluding atmospheric and receiver errors) exceeds “k” times the Galileo URA due to a common failure <ref>[https://www.gsc-europa.eu/sites/default/files/sites/all/files/Galileo-OS-SDD_v1.3.pdf Galileo OS SDD]</ref>. The MPLs for these probabilities (factor “k” being 4.17) are defined in the following table:

<div style="text-align:center;">
{| class="wikitable" style="display:inline-table;"
|+ style="caption-side:bottom;"|''Probability of SIS Fault and Probability of Constellation Fault MPLs''
! Parameter
! Value
|-
| style="text-align:center;" | GALILEO PROBABILITY OF SINGLE SIS FAULT (P<sub>sat</sub>)
| ≤ 3·10<sup>−5</sup>
|-
| style="text-align:center;" | GALILEO PROBABILITY OF CONSTELLATION N SIS FAULT (P<sub>const</sub>)
| ≤ 2·10<sup>−4</sup>
|}
</div>

For the [[Galileo High Accuracy Service (HAS)|High Accuracy Service (HAS)]], the MPLs are computed as the RMS over the instantaneous constellation average, for a period of 30 days:

<div style="text-align:center;">
{| class="wikitable" style="display:inline-table;"
|+ style="caption-side:bottom;"|''[https://www.gsc-europa.eu/sites/default/files/sites/all/files/Galileo-HAS-SDD_v1.0.pdf Galileo HAS Accuracy MPLs] for orbit, clock and code biases''
! FIGURE OF MERIT
! MPL – Galileo
! MPL – GPS
|-
| style="text-align:center;" | HAS orbit corrections accuracy
| ≤ 20cm (95%)
| ≤ 33cm (95%)
|-
| style="text-align:center;" | HAS clock corrections accuracy
| ≤ 12cm (95%)
| ≤ 15cm (95%)
|-
| style="text-align:center;" | HAS code biases accuracy
| colspan="2" style="text-align:center;" | ≤ 50cm (95%)
|}
</div>

Currently, the [[Galileo High Accuracy Service (HAS)|Galileo High Accuracy Service (HAS)]] meet these requirements with accuracy values of around 15 and 18 centimetres (Galileo and GPS respectively) for the orbit corrections, 7 and 10 centimetres for the clock corrections, and lower than 40 centimetres (both Galileo and GPS) for the code biases.

The following figures are an example of the accuracy achieved during the period from January 2025 to March 2025 (only Galileo):

<center>
<gallery widths=350 heights=150>
File:HAS accuracy of the Galileo orbit corrections.png|'''''HAS accuracy of the Galileo orbit corrections'''''
File:HAS accuracy of the Galileo clock corrections.png|'''''HAS accuracy of the Galileo clock corrections'''''
File:HAS accuracy of the Galileo code biases.png|'''''HAS accuracy of the Galileo code biases'''''
</gallery>
</center>

Refer to [https://www.gsc-europa.eu/electronic-library/performance-reports/galileo-high-accuracy-service-has EUSPA, Galileo HAS Performance Reports] for quarterly published performance reports of Galileo HAS.

Current Galileo SAR Service performance can be expressed in terms of MPLs for the contribution to the SAR Forward and Return link services as it is indicated in the [https://www.gsc-europa.eu/sites/default/files/sites/all/files/Galileo-SAR-SDD.pdf Galileo SAR Service Definition document].

The SAR MPLs are divided into SAR/Galileo Forward Link Service, SAR/Galileo Return Link Service, and SAR/Galileo Space Availability:

<div style="text-align:center;">
{| class="wikitable" style="display:inline-table;"
! SAR/GALILEO FORWARD LINK SERVICE
! style="text-align:center;" | TARGET VALUE
|-
| style="text-align:center;" | Forward Link Service Availability
| style="text-align:center;" | >99%
|-
| style="text-align:center;" | European MEOLUT Facility availability in Nominal mode
| style="text-align:center;" | >95%
|-
| style="text-align:center;" | European MEOLUT Facility availability in Degraded mode
| style="text-align:center;" | >97.5%
|-
| style="text-align:center;" | Detection probability: Valid Message
| style="text-align:center;" | >99%
|-
| style="text-align:center;" | Location probability within 5km (1–12 Bursts)
| style="text-align:center;" | >95%
|-
| style="text-align:center;" | Location probability within 5km (Single Burst)
| style="text-align:center;" | >90%
|-
| style="text-align:center;" | Location probability (Single Burst)
| style="text-align:center;" | >90%
|-
| style="text-align:center;" | Location probability (1–12 Bursts)
| style="text-align:center;" | >98%
|-
| style="text-align:center;" | Location probability within 2km (1–12 Bursts)
| style="text-align:center;" | >90%
|}
</div>

<div style="text-align:center;">
{| class="wikitable" style="display:inline-table;"
! SAR/GALILEO RETURN LINK SERVICE
! style="text-align:center;" | TARGET VALUE
|-
| style="text-align:center;" | Return Link Service Availability
| style="text-align:center;" | >95%
|-
| style="text-align:center;" | End-to-end Return Link Service Availability
| style="text-align:center;" | >90%
|-
| style="text-align:center;" | Galileo System Message Delivery Latency within 15 minutes
| style="text-align:center;" | >99%
|-
| style="text-align:center;" | End-to-end Message Delivery Loop Latency within 30 minutes
| style="text-align:center;" | >95%
|}
</div>

<div style="text-align:center;">
{| class="wikitable" style="display:inline-table;"
|+ style="caption-side:bottom;"|''[https://www.gsc-europa.eu/sites/default/files/sites/all/files/Galileo-SAR-SDD.pdf Galileo SAR MPLs]''
! SAR/GALILEO SPACE AVAILABILITY
! style="text-align:center;" | TARGET VALUE
|-
| style="text-align:center;" | SAR Repeater Availability
| style="text-align:center;" | >95%
|}
</div>

The SAR MPLs are currently mostly meet but variates with the location and the month. MPL fulfilment status dashboards for Detection and Location, Space Segment Availability, and Ground Segment Availability are published for each quarter of the year at the [https://www.gsc-europa.eu/electronic-library/performance-reports/search-and-rescue-sar-galileo-service EUSPA, Galileo SAR Performance Reports].

In the case of the [[Galileo Public Regulated Service (PRS)|Galileo Public Regulated Service (PRS)]], the [[GNSS Performances|performance]] requirements include horizontal and vertical [[Accuracy|accuracy]]. The [[Availability|availability]] of the service should be 99.5%.

See the article [[Galileo Performances|Galileo Performances]] for further information.

==Credits==
Edited by GMV, using information from ESA, European GNSS Service Centre and European Union as indicated through the references.

==Notes==
<references group="footnotes"/>
==References==
<references/>

[[Category:GALILEO|!]]

Galileo Signal Authentication Service

2026-09-16T12:34:26Z

Ignacio.Fernandez: added category tags

{{Article Infobox2
|Category=GALILEO
|Editors=European Commission
|YearOfPublication=2026
|Level=Intermediate
|Title={{Galileo Signal Authentication Service}}
}}

The [[GALILEO General Introduction|GALILEO]] System is an independent, global, European-controlled, satellite-based navigation system and provides a number of services to users equipped with Galileo-compatible receivers.<ref>[https://www.gsc-europa.eu/galileo/services Galileo Services on GSC website]</ref>

The GALILEO Signal Authentication Service (SAS) enables an authenticated positioning service by complementing the [[Galileo Open Service Navigation Message Authentication|Open Service Navigation Message Authentication (OSNMA)]] Service with E6-based ranging authentication capabilities. The SAS service is supported through a SAS server which is accessible through terrestrial means.

The Galileo Signal Authentication Service resulted from the re-scoping of the former Galileo Commercial Service (CS).<ref>[https://eur-lex.europa.eu/eli/dec_impl/2024/1882 Commission Implementing Decision (EU) 2024/1882]</ref> It is a free-of-charge service targeting civil applications, satisfying the demand for spoofing protection beyond the data authentication offered by OSNMA. The SAS service is currently under an initial testing capability, in view of an Initial Service declaration in 2027.

==Main Concept==

The SAS service offers ranging authentication based on the Galileo encrypted E6-C pilot signal component. Before operation, users can download so-called Re-Encrypted Code Sequences (RECS) from the SAS server. These RECS are subsequences of the E6-C encrypted signal, and re-encrypted using an OSNMA key that is only transmitted after the RECS.

During operation, a receiver records an E6-C signal snapshot of some tens of milliseconds. Then, after a delay, the OSNMA key is received that can be used to decrypt the RECS and to obtain the so-called ECS (Encrypted Code Sequence). The receiver can then correlate the ECS with the recorded snapshot for each satellite. Only in case of an authentic E6-C signal, a correlation peak can be found. The process is illustrated in the figure below. By making use of authenticated E6-C pseudoranges and authenticated E1B data, under some assumptions, a signal- and data-authenticated PVT can be obtained. Implementation aspects are discussed [[#Receiver Implementation Aspects|below]].

The core concept of SAS is that, although the RECS can be downloaded in advance, the ECS are only disclosed after their transmission (i.e. after the receiver has already recorded the snapshot). Thus, it is not possible for a spoofer to generate the authentic ECS in advance. As the delayed disclosure of the key vs. the RECS is part of the core concept, sufficiently accurate time synchronisation in the receiver is required, as is the case for OSNMA.<ref>[https://www.gsc-europa.eu/electronic-library/programme-reference-documents/galileo-in-force/osnma Galileo OSNMA Receiver Guidelines]</ref>

[[File:SAS_Processing_Steps.png|800px|center|thumb|Galileo SAS operation. Left: Download RECS from the server. Center: Capture an E6-C snapshot. Right: Decrypt RECS with OSNMA and perform a-posteriori correlation with E6-C snapshot.]]

==System Level Implementation==

At the signal-in-space level, the SAS service consists of the continuous encryption of the E6-C signal component as transmitted by Galileo satellites.

At the ground infrastructure level, the Galileo Service Centre hosts the SAS server which provides RECS, BGD and SLOG files on request:
* The RECS files contain the re-encrypted code sequences with a configurable duration (up to 16 milliseconds) and period (down to 200 milliseconds). The period corresponds to the Time Between Authentications (TBA). Furthermore, a configurable “randomisation flag” defines whether the start of the RECS within each period is predictable or not. The structure of a RECS period is shown in the figure below.
* The BGD (Broadcast Group Delay) files contain estimates of the BGDs that are required for applying I/NAV clock corrections to the E6-C pseudorange measurements obtained from the ECS correlations.
* The SLOG (SAS Status and Log) files provide SAS status information and related events.

Receivers can connect to the SAS server over HTTPS to request RECS, BGD and SLOG files using a query with the desired configuration parameters. The files can be requested for up to one week in advance, so the autonomy period for the user can be up to one week. The files are signed using official Galileo key material and receivers must verify these signatures. The SAS server also acts as an NTS (Network Time Security) server, offering authenticated time synchronisation.

[[File:SAS_RECS_Period.png|450px|center|thumb|Structure of a RECS period]]

==Receiver Implementation Aspects==

The full details of SAS, including the format of the server queries and the required cryptographic operations, will be described in the Galileo SAS interface specification and the Galileo SAS SDD (Service Definition Document), both to be published soon, or other Galileo documentation when the service is officially launched. Preliminary specifications have already been published but are subject to change.<ref>[https://doi.org/10.33012/2024.19707 I. Fernandez-Hernandez et al. “Galileo Signal Authentication Service (SAS)”. In Proceedings of the 37th International Technical Meeting of the Satellite Division of the Institute of Navigation (ION GNSS+ 2024), Baltimore, MD, USA, 16–20 September 2024, pp. 3292–3307.]</ref>

Galileo SAS allows the receiver to obtain authentic data through OSNMA and spreading code-protected E6-C measurements through the RECS correlation. These elements allow to compute an authenticated PVT solution under certain circumstances and assumptions. A SAS receiver may include techniques such as Vestigial Signal Search (VSS) to detect, and even mitigate, meaconing signals. Such aspects which need to be considered to obtain an authenticated PVT will be described in the Galileo SAS Receiver Guidelines document which will be published by the programme.

==Galileo SAS Roadmap==

The SAS roadmap consists of the following phases:
* Initial Capability (Phase 0): In this phase, E6-C encryption is activated first on the L3 satellites (GSAT0201 and GSAT0202) and then on the full constellation. Since December 2025, the E6-C encryption is activated permanently on the L3 satellites. During this phase, experimentation takes place using a prototype SAS server and prototype SAS receivers.
* Initial Service (Phase 1): The Initial Service Declaration in Phase 1 will allow global and free use of SAS. It is foreseen for 2027.
* Full Service (Phase 2): The Full Service Declaration will introduce improvements with respect to Phase 1. This is foreseen in the next years and is under consolidation with the Galileo 2nd Generation (G2G) schedule, including SAS improvements together with new authentication signals.

==References==
<references/>

[[Category:GALILEO|SAS]]
[[Category:GALILEO Services|SAS]]

Galileo Signal Authentication Service

2026-09-16T12:22:53Z

Ignacio.Fernandez: Images added

File:SAS RECS Period.png

2026-09-16T12:17:17Z

Ignacio.Fernandez: Structure of a RECS Period

== Summary ==
Structure of a RECS Period

File:SAS Processing Steps.png

2026-09-16T12:07:34Z

Ignacio.Fernandez: Galileo SAS operation

== Summary ==
Galileo SAS operation

Galileo Signal Authentication Service

2026-09-15T14:25:41Z

Ignacio.Fernandez: Internal link added, minor updates

{{Article Infobox2
|Category=GALILEO
|Editors=European Commission
|YearOfPublication=2026
|Level=Intermediate
|Title={{Galileo Signal Authentication Service}}
}}

The [[GALILEO General Introduction|GALILEO]] System is an independent, global, European-controlled, satellite-based navigation system and provides a number of services to users equipped with Galileo-compatible receivers.<ref>[https://www.gsc-europa.eu/galileo/services Galileo Services on GSC website]</ref>

The GALILEO Signal Authentication Service (SAS) enables an authenticated positioning service by complementing the [[Galileo Open Service Navigation Message Authentication|Open Service Navigation Message Authentication (OSNMA)]] Service with E6-based ranging authentication capabilities. The SAS service is supported through a SAS server which is accessible through terrestrial means.

The Galileo Signal Authentication Service resulted from the re-scoping of the former Galileo Commercial Service (CS).<ref>[https://eur-lex.europa.eu/eli/dec_impl/2024/1882 Commission Implementing Decision (EU) 2024/1882]</ref> It is a free-of-charge service targeting civil applications, satisfying the demand for spoofing protection beyond the data authentication offered by OSNMA. The SAS service is currently under an initial testing capability, in view of an Initial Service declaration in 2027.

==Main Concept==

The SAS service offers ranging authentication based on the Galileo encrypted E6-C pilot signal component. Before operation, users can download so-called Re-Encrypted Code Sequences (RECS) from the SAS server. These RECS are subsequences of the E6-C encrypted signal, and re-encrypted using an OSNMA key that is only transmitted after the RECS.

During operation, a receiver records an E6-C signal snapshot of some tens of milliseconds. Then, after a delay, the OSNMA key is received that can be used to decrypt the RECS and to obtain the so-called ECS (Encrypted Code Sequence). The receiver can then correlate the ECS with the recorded snapshot for each satellite. Only in case of an authentic E6-C signal, a correlation peak can be found. The process is illustrated in the figure below. By making use of authenticated E6-C pseudoranges and authenticated E1B data, under some assumptions, a signal- and data-authenticated PVT can be obtained. Implementation aspects are discussed [[#Receiver Implementation Aspects|below]].

The core concept of SAS is that, although the RECS can be downloaded in advance, the ECS are only disclosed after their transmission (i.e. after the receiver has already recorded the snapshot). Thus, it is not possible for a spoofer to generate the authentic ECS in advance. As the delayed disclosure of the key vs. the RECS is part of the core concept, sufficiently accurate time synchronisation in the receiver is required, as is the case for OSNMA.<ref>[https://www.gsc-europa.eu/electronic-library/programme-reference-documents/galileo-in-force/osnma Galileo OSNMA Receiver Guidelines]</ref>

==System Level Implementation==

At the signal-in-space level, the SAS service consists of the continuous encryption of the E6-C signal component as transmitted by Galileo satellites.

At the ground infrastructure level, the Galileo Service Centre hosts the SAS server which provides RECS, BGD and SLOG files on request:
* The RECS files contain the re-encrypted code sequences with a configurable duration (up to 16 milliseconds) and period (down to 200 milliseconds). The period corresponds to the Time Between Authentications (TBA). Furthermore, a configurable “randomisation flag” defines whether the start of the RECS within each period is predictable or not. The structure of a RECS period is shown in the figure below.
* The BGD (Broadcast Group Delay) files contain estimates of the BGDs that are required for applying I/NAV clock corrections to the E6-C pseudorange measurements obtained from the ECS correlations.
* The SLOG (SAS Status and Log) files provide SAS status information and related events.

Receivers can connect to the SAS server over HTTPS to request RECS, BGD and SLOG files using a query with the desired configuration parameters. The files can be requested for up to one week in advance, so the autonomy period for the user can be up to one week. The files are signed using official Galileo key material and receivers must verify these signatures. The SAS server also acts as an NTS (Network Time Security) server, offering authenticated time synchronisation.

==Receiver Implementation Aspects==

The full details of SAS, including the format of the server queries and the required cryptographic operations, will be described in the Galileo SAS interface specification and the Galileo SAS SDD (Service Definition Document), both to be published soon, or other Galileo documentation when the service is officially launched. Preliminary specifications have already been published but are subject to change.<ref>[https://doi.org/10.33012/2024.19707 I. Fernandez-Hernandez et al. “Galileo Signal Authentication Service (SAS)”. In Proceedings of the 37th International Technical Meeting of the Satellite Division of the Institute of Navigation (ION GNSS+ 2024), Baltimore, MD, USA, 16–20 September 2024, pp. 3292–3307.]</ref>

Galileo SAS allows the receiver to obtain authentic data through OSNMA and spreading code-protected E6-C measurements through the RECS correlation. These elements allow to compute an authenticated PVT solution under certain circumstances and assumptions. A SAS receiver may include techniques such as Vestigial Signal Search (VSS) to detect, and even mitigate, meaconing signals. Such aspects which need to be considered to obtain an authenticated PVT will be described in the Galileo SAS Receiver Guidelines document which will be published by the programme.

==Galileo SAS Roadmap==

The SAS roadmap consists of the following phases:
* Initial Capability (Phase 0): In this phase, E6-C encryption is activated first on the L3 satellites (GSAT0201 and GSAT0202) and then on the full constellation. Since December 2025, the E6-C encryption is activated permanently on the L3 satellites. During this phase, experimentation takes place using a prototype SAS server and prototype SAS receivers.
* Initial Service (Phase 1): The Initial Service Declaration in Phase 1 will allow global and free use of SAS. It is foreseen for 2027.
* Full Service (Phase 2): The Full Service Declaration will introduce improvements with respect to Phase 1. This is foreseen in the next years and is under consolidation with the Galileo 2nd Generation (G2G) schedule, including SAS improvements together with new authentication signals.

==References==
<references/>

Galileo Signal Authentication Service

2026-09-15T14:04:08Z

Ignacio.Fernandez: New content

{{Article Infobox2
|Category=GALILEO
|Editors=European Commission
|YearOfPublication=2026
|Level=Intermediate
|Title={{Galileo Signal Authentication Service}}
}}

The [[GALILEO General Introduction|GALILEO]] System is an independent, global, European-controlled, satellite-based navigation system and provides a number of services to users equipped with Galileo-compatible receivers.<ref>[https://www.gsc-europa.eu/galileo/services Galileo Services on GSC website]</ref>

The GALILEO Signal Authentication Service (SAS) enables an authenticated positioning service by complementing the [[Galileo Open Service Navigation Message Authentication|Open Service Navigation Message Authentication (OSNMA)]] Service with E6-based ranging authentication capabilities. The SAS service is supported through a SAS server which is accessible through terrestrial means.

The Galileo Signal Authentication Service resulted from the re-scoping of the former Galileo Commercial Service (CS).<ref>[https://eur-lex.europa.eu/eli/dec_impl/2024/1882 Commission Implementing Decision (EU) 2024/1882]</ref> It is a free-of-charge service targeting civil applications, satisfying the demand for spoofing protection beyond the data authentication offered by OSNMA. The SAS service is currently under an initial testing capability, in view of an Initial Service declaration in 2027.

==Main Concept==

The SAS service offers ranging authentication based on the Galileo encrypted E6-C pilot signal component. Before operation, users can download so-called Re-Encrypted Code Sequences (RECS) from the SAS server. These RECS are subsequences of the E6-C encrypted signal, and re-encrypted using an OSNMA key that is only transmitted after the RECS.

During operation, a receiver records an E6-C signal snapshot of some tens of milliseconds. Then, after a delay, the OSNMA key is received that can be used to decrypt the RECS and to obtain the so called ECS (Encrypted Code Sequence). The receiver can then correlate the ECS with the recorded snapshot for each satellite. Only in case of an authentic E6-C signal, a correlation peak can be found. The process is illustrated in the figure below. By making use of authenticated E6-C pseudoranges and authenticated E1B data, under some assumptions, a signal- and data-authenticated PVT can be obtained. Implementation aspects are discussed further below.

The core concept of SAS is that, although the RECS can be downloaded in advance, the ECS are only disclosed after their transmission (i.e., after the receiver has already recorded the snapshot). Thus, it is not possible for a spoofer to generate the authentic ECS in advance. As the delayed disclosure of the key vs. the RECS is part of the core concept, sufficiently accurate time synchronisation in the receiver is required, as is the case for OSNMA.<ref>[https://www.gsc-europa.eu/electronic-library/programme-reference-documents/galileo-in-force/osnma Galileo OSNMA Receiver Guidelines]</ref>

==System Level Implementation==

At the signal-in-space level, the SAS service consists of the continuous encryption of the E6-C signal component as transmitted by Galileo satellites.

At the ground infrastructure level, the Galileo Service Centre hosts the SAS server which provides RECS, BGD and SLOG files on request:
* The RECS files contain the re-encrypted code sequences with a configurable duration (up to 16 milliseconds) and period (down to 200 milliseconds). The period corresponds to the Time Between Authentications (TBA). Furthermore, a configurable “randomisation flag” defines whether the start of the RECS within each period is predictable or not. The structure of a RECS period is shown in the figure below.
* The BGD (Broadcast Group Delay) files contain estimates of the BGDs that are required for applying I/NAV clock corrections to the E6-C pseudorange measurements obtained from the ECS correlations.
* The SLOG (SAS Status and Log) files provide SAS status information and related events.

Receivers can connect to the SAS server over HTTPS to request RECS, BGD and SLOG files using a query with the desired configuration parameters. The files can be requested for up to one week in advance, so the autonomy period for the user can be up to one week. The files are signed using official Galileo key material and receivers must verify these signatures. The SAS server also acts as a NTS (Network Time Security) server, offering authenticated time synchronisation.

==Receiver Implementation Aspects==

The full details of SAS, including the format of the server queries and the required cryptographic operations, will be described in the Galileo SAS interface specification and the Galileo SAS SDD (Service Definition Document), both to be published soon, or other Galileo documentation when the service is officially launched. Preliminary specifications have already been published but are subject to change.<ref>[https://doi.org/10.33012/2024.19707 I. Fernandez-Hernandez et al. “Galileo Signal Authentication Service (SAS)”. In Proceedings of the 37th International Technical Meeting of the Satellite Division of the Institute of Navigation (ION GNSS+ 2024), Baltimore, MD, USA, 16–20 September 2024, pp. 3292–3307.]</ref>

Galileo SAS allows the receiver to obtain authentic data through OSNMA and spreading code-protected E6-C measurements through the RECS correlation. These elements allow to compute an authenticated PVT solution under certain circumstances and assumptions. A SAS receiver may include techniques such as Vestigial Signal Search (VSS) to detect, and even mitigate, meaconing signals. Such aspects which need to be considered to obtain an authenticated PVT will be described in the Galileo SAS Receiver Guidelines document which will be published by the programme.

==Galileo SAS Roadmap==

The SAS roadmap consists of the following phases:
* Initial Capability (Phase 0): In this phase, E6-C encryption is activated first on the L3 satellites (GSAT0201 and GSAT0202) and then on the full constellation. Since December 2025, the E6-C encryption is activated permanently on the L3 satellites. During this phase, experimentation takes place using a prototype SAS server and prototype SAS receivers.
* Initial Service (Phase 1): The Initial Service Declaration in Phase 1 will allow global and free use of SAS. It is foreseen for 2027.
* Full Service (Phase 2): The Full Service Declaration will introduce improvements with respect to Phase 1. This is foreseen in the next years and is under consolidation with the Galileo 2nd Generation (G2G) schedule, including SAS improvements together with new authentication signals.

==References==
<references/>