Over the last years the awareness about jamming and spoofing risks has been increasing, particularly in the timing community since they may cause the disruption of critical services and infrastructures in the Telecommunication, Energy and Finance sectors that rely on GNSS timing to operate. In order to overcome these hazards, the European GNSS Agency (GSA) has funded the development of timing receivers for professional applications, with the aim to address specifically the above vulnerabilities, improve the receiver robustness and the accuracy and reliability of time transfer. In this context the GIANO (Galileo-based timing Receiver for Critical infrastructures robustness) project consortium, coordinated by Thales Alenia Space (TAS) Italy and with the support of Deimos Engenharia S.A. (Portugal), the Space Research Centre PAS in Poznan (Poland), Piktime System SP. Zoo (Poland) and Business Integration Partner S.p.A. (Italy), has been awarded a contract in the framework of the GSA’s “Fundamental Elements” program to develop a timing receiver for critical infrastructure applications. Besides the implementation of some interference and spoofing detection and mitigation techniques, GIANO receiver makes use of Galileo’s authentication service OSNMA (Open Service Navigation Message Authentication), which can be employed as an added defense against some types of spoofing. OSNMA exploits TESLA (Time Efficient Stream Loss-tolerant Authentication) scheme, which is a protocol based on the transmission of message authentication codes generated with a key that is broadcast with some delay. The receiver authenticates the satellite messages through a Digital Signature algorithm and a public key known by the receivers, which also validates the root key of the TESLA chain, and through MACs (Message Authentication Codes) which are used to authenticate specific fields of the Navigation Message. The receiver will also support public key renewals over the air. In this paper, the OSNMA implementation within GIANO receiver, including the cryptographic operations required is presented. The GIANO OSNMA capability will be extensively tested and validated with the support of European Commission Joint Research Centre (Ispra, Italy).