Azure SQL Database Always Encrypted is a security feature designed to protect sensitive data stored in Azure SQL databases by ensuring that encryption keys are never revealed to the Database Engine. This means that data remains encrypted both at rest and in transit, with decryption only occurring o…Azure SQL Database Always Encrypted is a security feature designed to protect sensitive data stored in Azure SQL databases by ensuring that encryption keys are never revealed to the Database Engine. This means that data remains encrypted both at rest and in transit, with decryption only occurring on the client side where the application resides.
The feature operates using two types of keys: Column Master Keys (CMK) and Column Encryption Keys (CEK). The CMK is stored outside of Azure SQL Database, typically in Azure Key Vault, Windows Certificate Store, or a Hardware Security Module (HSM). The CEK is used to encrypt the actual data and is itself encrypted by the CMK before being stored in the database metadata.
Always Encrypted supports two encryption types: Deterministic and Randomized. Deterministic encryption generates the same encrypted value for any given plain text value, enabling equality comparisons, point lookups, joins, and grouping operations on encrypted columns. Randomized encryption uses a more secure method that generates different encrypted values for the same input, providing stronger protection but limiting query operations to basic retrieval.
The client application uses an Always Encrypted-enabled driver that handles encryption and decryption operations transparently. When data is inserted, the driver encrypts values before sending them to the database. When data is retrieved, the driver decrypts the values before returning them to the application.
Key benefits include protection against unauthorized database administrators and cloud operators who have access to the database but should not view sensitive data. This addresses compliance requirements for regulations like GDPR, HIPAA, and PCI DSS.
Implementation considerations include ensuring client applications have access to the CMK, understanding query limitations on encrypted columns, and planning for key rotation procedures. Azure SQL Database Always Encrypted provides a robust solution for organizations requiring strong data protection while maintaining application functionality.
Always Encrypted is a critical security feature designed to protect sensitive data in Azure SQL Database. It ensures that sensitive information such as credit card numbers, national identification numbers, and healthcare data remains encrypted at all times - both at rest and in transit. The key differentiator is that the data remains encrypted even from database administrators and cloud operators, providing true separation of data ownership from data management.
What is Always Encrypted?
Always Encrypted is a client-side encryption technology that allows clients to encrypt sensitive data inside client applications and never reveal the encryption keys to the SQL Database Engine. This creates a separation between those who own the data (and can view it) and those who manage the data (but should have no access).
There are two types of encryption supported: - Deterministic encryption: Always generates the same encrypted value for any given plain text value. This allows equality comparisons, grouping, and indexing on encrypted columns. - Randomized encryption: Uses a method that encrypts data in a less predictable manner. It is more secure but prevents searching, grouping, indexing, and joining on encrypted columns.
How Always Encrypted Works
Always Encrypted uses two types of keys:
1. Column Encryption Keys (CEK): These keys are used to encrypt data in the columns. They are stored in the database in encrypted form.
2. Column Master Keys (CMK): These keys protect the Column Encryption Keys. They are stored outside of the database in a trusted key store such as Azure Key Vault, Windows Certificate Store, or a Hardware Security Module (HSM).
The encryption and decryption process occurs on the client side through an Always Encrypted-enabled driver. The database engine never sees the plaintext data or the encryption keys. When a query is executed, the driver encrypts the parameters before sending them to the database and decrypts the results before returning them to the application.
Key Components and Architecture
- The client application must use an Always Encrypted-enabled driver (such as .NET Framework Data Provider for SQL Server version 4.6 or later) - Encryption keys are managed by the client, not the database - The database stores only encrypted values and encrypted CEKs - Azure Key Vault is the recommended location for storing CMKs in Azure environments
Exam Tips: Answering Questions on Azure SQL Database Always Encrypted
Key Concepts to Remember:
1. Client-side encryption: Always remember that encryption and decryption happen on the client side, not the server side. The SQL Database Engine never has access to plaintext data.
2. Two-key hierarchy: Memorize that CMK protects CEK, and CEK encrypts the actual data. CMK is stored externally (Azure Key Vault), while encrypted CEK is stored in the database.
3. Encryption types: Deterministic allows equality operations but is less secure. Randomized is more secure but limits query operations. Choose based on the scenario requirements.
4. Use cases: Always Encrypted is ideal when you need to protect data from database administrators or when regulatory compliance requires separation of duties.
5. Limitations: Remember that Always Encrypted does not support all SQL operations on encrypted columns. Range queries, LIKE operations, and calculations are not supported.
Common Exam Scenarios:
- When asked about protecting data from DBAs, Always Encrypted is typically the correct answer - When the scenario mentions client-side encryption for SQL Database, think Always Encrypted - If a question mentions Azure Key Vault with SQL Database encryption keys, Always Encrypted with CMK stored in Key Vault is likely the answer - For scenarios requiring searchable encrypted data, choose deterministic encryption - For maximum security where searching is not required, choose randomized encryption
Distinguishing from Other Features:
- Transparent Data Encryption (TDE): Encrypts data at rest but DBAs can still see plaintext data. Use this for encryption at rest only. - Dynamic Data Masking: Masks data in query results but does not encrypt it. Use this for obfuscation, not encryption. - Always Encrypted: True client-side encryption where even DBAs cannot see plaintext. Use this for maximum data protection.