This study aims to develop an authentication algorithm for Routable-GOOSE (R-GOOSE) or Routable-SV (R-SV). Critical security features must be enabled to support authentication and authorization. The EtM algorithm is proposed for maintaining message confidentiality and integrity, with AES-128 encryption for privacy and MAC algorithms for message authentication. Simulation results indicate that the EtM algorithm can be successfully used for R-SV messages while meeting the stringent 3 ms latency criteria. The results suggest that future IEC 62351 security standards can confidently advocate for encryption for R-SV communication.