# What is SGX (Software Guard eXtensions)?

**It is a TEE** (Trusted Execution Environment). **Everything outside the processor chip is not trusted.** In particular, the **BIOS** (Basic Input/Output System), the **SMM** (System Management Mode, ring -2), the **ME** (Intel Management Engine, ring -3), and the **OS** (Operating System, ring 0) **are not trusted**.

**The SGX code and data are put inside a special container** (an SGX enclave). The contents of the enclave are **signed** (they are loaded from an untrusted source…) and **can be attested by an external third party**. The contents of the enclave are **isolated** from the rest of the system. The enclave code runs in **ring** **3** (least privileged mode). 

All **SGX instructions** are implemented in **microcode** (**potential attack vector**).


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