What protocol is commonly used to allow for secured tunnels between corporate networks through untrusted networks?

IPSec virtual private networks are commonly established to tunnel through public or untrusted networks. A RTOS, or real-time operating system, is used for embedded systems. SHA-1 is a hashing algorithm, and RSA is an encryption algorithm that is used for IPSec as part of its authentication process. IPSec tunnels themselves commonly use AES, but may use other algorithms as well.