AWS Nitro Enclaves

An enclave is a separate virtual machine with its own kernel, memory, and CPU cores, carved out of a parent EC2 instance. The Nitro Hypervisor enforces strict isolation, ensuring no process on the parent instance—not even an administrator with root access—can read the enclave's memory or code. This creates a hardware-rooted trust boundary that is significantly smaller and more auditable than the full instance.

Before an external service sends sensitive data to an enclave, it must verify the enclave's identity. The Nitro Secure Module (NSM) generates a cryptographically signed attestation document containing:

• A hash of the enclave image (proof of code identity)
• The enclave's public key
• Platform configuration registers (PCRs) This allows a relying party to establish a hardware-rooted chain of trust and ensure only authorized code processes their data.

Enclaves have no external network interfaces. The only communication channel is a local VSOCK socket to the parent instance. This forces a secure proxy architecture:

• The parent instance acts as a network proxy, filtering and forwarding traffic
• The enclave never sees a raw network packet
• All ingress/egress is explicitly controlled by the parent's application logic This design eliminates entire classes of remote network attacks against the enclave itself.

Since enclaves have no persistent storage, any state that must survive a restart must be encrypted and stored externally. Sealing binds encrypted data to the specific enclave identity and platform:

• Data encrypted by an enclave can only be decrypted by the exact same enclave on the same hardware
• Prevents replay attacks and cross-platform data theft
• Enables secure state persistence without trusting the parent instance's filesystem

The TCB of a Nitro Enclave is dramatically smaller than a full Linux instance. It includes only:

• The Nitro Hypervisor (a lightweight, formally verified component)
• The enclave's minimal kernel and application
• The NSM for attestation Excluded from the TCB: the parent OS, AWS operators, the host hypervisor, and all management software. This radical reduction in attack surface is the core value proposition for regulated workloads.