What is Galileo OSNMA?

Open Service Navigation Message Authentication (OSNMA) is a data authentication function for the Galileo Open Service worldwide users, freely accessible to all. OSNMA provides receivers with the assurance that the received Galileo navigation message is coming from the system itself and has not been modified.

OSNMA is authenticating data for geolocation information from the Open Service through the Navigation Message (I/NAV) broadcast on the E1-B signal component. This is realised by transmitting authentication-specific data in previously reserved fields of the E1 I/NAV message. By using these fields, OSNMA does not introduce any overhead to the system, thus the OS navigation performance remains untouched.

Additional details about service characterisation, potential target markets and roadmap of the OSNMA service can be found in Galileo OSNMA Info Note.

Galileo OSNMA scheme

OSNMA adapts an existing standard lightweight broadcast authentication protocol named TESLA (Timed-Efficient Stream Loss-Tolerant Authentication) for optimal transmission through Galileo.

An OSNMA capable receiver differs from a generic OS receiver by the additional capabilities required to:

  1. Retrieve the OSNMA dedicated fields in the navigation message.
  2. Process these data to confirm whether the data is authentic.
  3. Implement a time synchronization requirement to ensure that the receiver is synchronised with the Galileo System Time (GST) from below 15 seconds to a few minutes, depending on the operating mode, before receiving and processing OSNMA information.
  4. Maintain the integrity of the stored OSNMA cryptographic material (confidentiality is not required).

Figure 1: OSNMA scheme

Additional details about OSNMA processing logic can be found in the Galileo OSNMA Info Note. Details regarding the processing the receiver cryptographic operations are provided in the OSNMA receiver guidelines.

Galileo OSNMA user segment

To achieve data authentication at user level, the receiver OSNMA implementation shall be compliant with the requirements provided in the OSNMA receiver guidelines.

To benefit from the OSNMA, the receiver must be able to perform the key management activities which consist of:

  1. Receiver initialisation: installing and storing the certified cryptographic material in the user receiver. This is a one-off operation, requiring a connection to the GSC that will provide the necessary material.
  2. Receiver key renewal/update: renewing or updating the public key stored in the receiver. This operation can be performed through over-the-air rekeying (OTAR) transmitted as part of the Signal In Space (SIS) authentication data or through contacting the OSNMA server in GSC, which will keep the history of the public keys.

OSNMA is based on a delayed disclosure protocol. This means that it needs to guarantee that the receiver internal time is not off by a certain amount versus GST. More details can be found in the receiver guidelines.

OSNMA user community can find additional information and functions through the GSC, which plays a central role in the OSNMA chain by publishing:

  • OSNMA public keys, crypto material, and associated certificates.
  • Notifications, and information updates on the OSNMA service status for all user communities.
  • NAGUs and Service Notices about planned public key renewal, unplanned public key revocation, planned key chain renewal and unplanned key chain revocation, and any service incident will be available for the service phase.

OSNMA users can find more details on how to retrieve the OSNMA cryptographic material and associated certificates from the GSC interface (GSC website and OSNMA SFTP server) and the EUSPA web portal on the OSNMA Internet Data Distribution (IDD) ICD.

Galileo OSNMA roadmap

The deployment of the Galileo OSNMA capability follows the roadmap presented below:

Figure 2: Galileo OSNMA implementation roadmap

Galileo OSNMA target markets

The following picture provides an overview of the most relevant market segments and applications that can benefit from Galileo OSNMA authentication feature:

Figure 3: Summary of most relevant Galileo OSNMA target applications


Additional details about target applications that will benefit from Galileo OSNMA can be found in the Galileo OSNMA Info Note.

Global GNSS market trends are published in the EUSPA EO & GNSS Market Report 2024 and information about needs per market segment can be found in Reports on User Needs and Requirements.

Any question?

A compilation of the most common questions can be found in the dedicated section for the OSNMA Frequently Asked Questions (FAQ). For any additional information, please contact our Galileo Helpdesk at helpdesk@gsc-europa.eu or directly through the Galileo Helpdesk form.