The purchaser may award a contract without prior advertising or competitive tendering where the contract can only be awarded to a specific economic operator, for reasons relating to the protection of exclusive rights, or for technical reasons such as, for example, specific interoperability or security requirements that must be met in order to guarantee the operation of armed forces or security forces, or the strict technical impossibility, for a candidate other than the successful economic operator, of achieving the required objectives, or the need to have recourse to specific know-how, tools or resources available only to a single operator, particularly in the case of retrofitting or retrofitting particularly complex equipment.