Always Encrypted Secure Enclaves

Secure enclaves represent a significant advancement in Always Encrypted, providing a hardware-backed trusted execution environment (TEE) to perform cryptographic operations directly within SQL Server. This enhances security by ensuring that sensitive data remains encrypted even in memory, protecting it from privileged code, including the SQL Server engine itself and administrators.

What are Secure Enclaves?

A secure enclave is a protected region of memory within the SQL Server process, isolated from the rest of the operating system and other applications. It runs specialized code designed to handle cryptographic operations like encryption, decryption, and comparison of encrypted data, using keys that never leave the enclave.

Benefits of Using Secure Enclaves:

• Enhanced Data Protection: Sensitive data is protected even from system administrators and privileged software.
• Confidential Computing: Enables processing of sensitive data in a confidential manner.
• Secure Key Handling: Cryptographic keys are generated, stored, and used exclusively within the enclave, never exposed to the host environment.
• Rich Querying Capabilities: Allows for more complex operations on encrypted data, such as pattern matching and range comparisons.

How Secure Enclaves Work:

Secure enclaves leverage hardware-based trusted execution technologies, such as Intel® Software Guard Extensions (SGX) or AMD Secure Encrypted Virtualization (SEV). When Always Encrypted with secure enclaves is enabled, the following process occurs:

1. Enclave Initialization: SQL Server initializes a secure enclave on the host machine.
2. Key Import: Encryption keys are securely imported into the enclave.
3. Data Processing: When sensitive data needs to be processed (e.g., for queries), it's sent to the enclave for decryption and processing.
4. Encrypted Output: Results or modified data are encrypted by the enclave before being returned to the SQL Server engine.

Supported Operations:

Secure enclaves unlock more advanced cryptographic operations for encrypted columns, including:

• Deterministic Encryption: Enhanced for secure enclave operations, allowing for equality comparisons.
• Randomized Encryption: Can now be used with secure enclaves for richer comparison operations.
• Range Comparisons: Perform queries like >, <, BETWEEN on encrypted columns.
• Pattern Matching: Use LIKE operator with encrypted data.
• Joining on Encrypted Data: Efficiently join tables based on encrypted columns.

Setting up Secure Enclaves:

Implementing secure enclaves involves several steps:

1. Hardware and Software Prerequisites: Ensure your server hardware supports SGX or SEV, and your SQL Server version is compatible.
2. Enclave Configuration: Configure SQL Server to enable secure enclave support. This often involves setting specific registry keys or service configurations.
3. Key Management: Utilize a Key Vault or other secure key management solution that integrates with secure enclaves.
4. Client Application Configuration: Update your client applications to enable the secure enclave feature when connecting to SQL Server.

Considerations and Limitations:

• Performance Overhead: While designed for efficiency, enclave operations can introduce some performance overhead compared to plaintext operations.
• Complexity: Setup and management of secure enclaves are more complex than standard Always Encrypted.
• Hardware Dependency: Relies on specific hardware capabilities.
• Limited Data Types: Not all data types or operations are supported within the enclave.

Further Reading:

• Microsoft Docs: Always Encrypted with Secure Enclaves
• Intel SGX Documentation