Which encryption mechanism is specifically designed to protect data as it exists in memory, preventing untrusted processes from decoding it?

The appropriate encryption mechanism designed to protect data in memory, safeguarding it from untrusted processes, is Software Guard Extensions (SGX). SGX is an Intel technology that creates secure enclaves within the main memory, allowing applications to run code and store data securely, even in the presence of potentially malicious software that may have access to the operating system or hypervisor.

Through SGX, sensitive information can be isolated in these enclaves, ensuring that only authorized processes can access or interpret the data. This offers a significant advantage over traditional encryption methods, as it protects data not just at rest or in transit but specifically while it is actively being processed in memory.

By focusing on memory integrity and ensuring that only trusted applications operate within these secure enclaves, SGX mitigates the risk of data breaches from untrusted code that might otherwise access memory directly. This makes it an essential technology in scenarios where data security is critical, especially in cloud computing or environments where multiple tenants may share hardware resources.

The other choices, while relevant to broader categories of data security, do not specifically address the unique challenges associated with protecting data in memory against untrusted processes.