CYSEC ARCA SATLINK is a software implementation of the Space Data Link Security (SDLS) protocol defined by the Consultative Committee for Space Data Systems (CCSDS). It provides end-to-end cryptographic protection for satellite telemetry/telecommand (TM/TC) and payload data links, covering both ground segment and on-board (flight software) environments. The product addresses the widespread practice of satellite operators communicating with spacecraft without link-level security, leaving TM/TC and payload data exposed to eavesdropping and unauthorized control. ARCA SATLINK applies security at the frame level of one or multiple virtual channels, equivalent to an L2 VPN (point-to-point), in line with the SDLS and SDLS-EP standards. Key functional areas include: - Cryptographic functions: encryption and authentication of data links - Key management: Over-The-Air Rekeying (OTAR) and full key lifecycle management - Security associations: management and monitoring of cryptographic associations - Anti-replay mitigations: protection against replay attacks on data links - Monitoring and control: visibility into the security state of data links ARCA SATLINK exposes cryptographic APIs designed to be accessible to space engineers without deep cryptography expertise, allowing integration into existing ground segment and flight software architectures. It operates independently of the underlying communications protocol, supporting CCSDS, CSP, and others. The product has been tested in space as part of a European Space Agency project and has been contracted by both ESA and CNES for in-orbit demonstrations.