Increasingly complex and powerful Systems-on-Chips (SoCs), connected through a 5G network, form the basis of the Internet-of-Things (IoT). These technologies will drive the digitalization in all domains, e.g. industry automation, automotive, avionics, and healthcare. A major requirement for all above domains is the long-term (10 to 30 years) secure communication between the SoCs and the cloud over public 5G networks. The foreseeable breakthrough of quantum computers represents a risk for all communication. In order to prepare for such an event, SoCs must integrate secure quantum-computer-resistant cryptography which is reliable and protected against SW and HW attacks. Empowering SoCs with such strong security poses a challenging problem due to limited resources, tight performance requirements and long-term life-cycles. While current works are focused on efficient implementations of post-quantum cryptography, implementation-security and reliability aspects for SoCs are still largely unexplored. To this end, we present three contributions. First, we present a RISC-V co-processor for post-quantum security, able to support lattice-based cryptography. Second, we use HW/SW co-design techniques to accelerate the NTT transformation and hash generation. Third, we perform the fault analysis of the implementation. We show that our coprocessor achieves high reliability and security capabilities while preserving good performance.