The “Always Encrypted” feature in SQL Server is a robust feature designed to protect our sensitive and valuable data, such as Social Security Numbers, Credit Card Details, or National IDs, from unauthorised access — even from database administrators (DBAs). In this article, we aim to explain each point, from the introduction to the configuration step, with a few examples and common pitfalls. I hope it will help you to protect your SQL Server data with the help of Always Encrypted.
Table of Contents
📌 Introduction to Always Encrypted
Always Encrypted is a data protection technology introduced in Microsoft SQL Server that helps protect our valuable and sensitive data. It stores data encrypted and remains encrypted during transport, at rest, and even during query processing. In Always Encrypted, Encryption and decryption of data occur on the client side, providing a higher level of data privacy and security.
🕰️ A Glimpse into History
The Always Encrypted was Introduced in SQL Server 2016.
Designed to address compliance requirements like HIPAA, GDPR, and PCI DSS.
Enhanced with Secure Enclaves in SQL Server 2019 and later, allowing richer query capabilities on encrypted columns.
✅ Advantages of Always Encrypted
A few advantages of Always Encrypted are given below for more clarity:
✅ Enhanced Security: Even DBAs can’t view plaintext data without proper access.
✅ Compliance-Friendly: Helps meet data protection standards across various industries.
✅ End-to-End Protection: Data remains encrypted in memory, disk, and transit.
✅ Client-Side Decryption: Keeps encryption keys away from the server.
❌ Disadvantages of Always Encrypted
A few disadvantages of Always Encrypted are given below for more clarity:
❌ Limited Operations: Only equality comparisons are supported unless Secure Enclaves are used.
❌ Performance Overhead: Encryption and decryption of data occur on the client side, which impacts performance.
❌ Tooling Restrictions: Not all tools or drivers support Always Encrypted.
❌ Complex Key Management: Requires secure storage and handling of Column Master Keys.
🔐 Required Permissions
- To configure Always Encrypted, a user needs:
- CONTROL permission on the database.
- ALTER ANY COLUMN MASTER KEY and ALTER ANY COLUMN ENCRYPTION KEY.
- CREATE CERTIFICATE/ASYMMETRIC KEY permission for key creation.
📌 When is Always Encrypted Needed?
- Storing personally identifiable information (PII).
- Handling credit card numbers, SSNs, or health records.
- Meeting regulatory standards like GDPR, HIPAA, and PCI DSS.
- When DBAs or admins should not have access to actual data values.
🧠 Best Practices for Always Encrypted
Here are the Best Practices for Always Encrypted in SQL Server to ensure data protection, performance, and maintainability:
✅ Choose the Right Encryption Type
- Use Deterministic Encryption when you need to perform equality comparisons, joins, or grouping.
- Use Randomized Encryption for highly sensitive data that doesn’t require querying.
✅ Store Keys Securely
Store Column Master Keys (CMKs) in a secure external location such as:
- Windows Certificate Store (Local Machine/User)
- Azure Key Vault
- Avoid storing keys directly on the SQL Server machine.
✅ Use Secure Enclaves When Needed
Enable Secure Enclaves (available in SQL Server 2019+) for operations such as:
- Range queries
- Pattern matching (LIKE)
- Sorting and indexing on encrypted columns
✅ Encrypt Only Sensitive Columns
Do not encrypt entire tables. Encrypt only those columns that:
- Contain PII (e.g., SSNs, credit card numbers)
- Require compliance with standards like HIPAA, GDPR, and PCI DSS.
✅ Use the Latin1_General_BIN2 Collation
For character-based encrypted columns, use:
COLLATE Latin1_General_BIN2Ensures compatibility and optimal performance with Always Encrypted.
✅ Avoid Using Functions on Encrypted Columns
Do not use SQL Server functions like LEN(), SUBSTRING(), UPPER(), etc., on encrypted data.
Move data transformation logic to the application layer.
✅ Regularly Rotate Encryption Keys
Periodically rotate CEKs and CMKs as part of your security hygiene.
Use the ALTER COLUMN with a new CEK to re-encrypt data.
✅ Use Supported Clients & Drivers
Only access encrypted columns with the following:
- SSMS 17.0+
- .NET Framework 4.6+
- ODBC Driver 13+
- JDBC Driver 6.0+
✅ Implement Key Backup and Recovery Procedures
Back up CMKs securely and document their storage paths.
Without access to CMKs, you will lose the ability to decrypt data permanently.
✅ Enable Always Encrypted During Insert/Update
Use parameterized queries or SQL command objects that support AE.
SSMS or your application client must have AE-enabled drivers or options.
✅ Avoid Encryption on Frequently Queried Columns (if possible)
Encrypted columns have performance overhead.
Design schema so that frequently used filters (e.g., search or join columns) remain unencrypted, or use Secure Enclaves if available.
✅ Audit and Monitor Access
Use SQL Server Audit or Extended Events to monitor:
- CMK/CEK access
- Encrypted column usage
✅ Always Test in a Lower Environment First
Before enabling AE in production, test:
- Key creation
- Column encryption
- Application compatibility
- Query performance
✅ Document Everything
Always document each & every details for safer side:
- CMK paths
- CEK names and associated columns
- Certificate expiry dates
- Rotation schedules
✅ Keep Up with SQL Server Updates
Always use the latest supported version of SQL Server and SSMS, as Microsoft continuously improves AE support and adds new capabilities (like enclave enhancements).
✅ Prerequisites
- SQL Server 2016 or later.
- SSMS version 17.0 or later (SSMS 21 recommended for latest features)
- The column to be encrypted should use supported data types (e.g., char, varchar, int, datetime)
- You must have ALTER, CONTROL, or db_owner permissions on the database.
⚙️ Steps to Configure Always Encrypted
Below are the steps to Configure Always Encrypted in SQL Server:
🔹 Step 1: Open SQL Server Management Studio
Connect to your SQL Server instance.
Expand the Databases node.
Expand the database where the table with sensitive data resides.
🔹 Step 2: Right-Click on Table ➤ Choose “Encrypt Columns”
Navigate to the table you want to protect.
Right-click the table and select Encrypt Columns…
It’ll launch the Always Encrypted Wizard.
🔹 Step 3: Select Columns for Encryption
In the wizard’s “Column Selection” step:
Check the box next to the columns you wish to encrypt (e.g., Social Security Number, Credit Card Number, Salary).
We can also select multiple columns.
Choose the encryption type:
Deterministic: Supports equality comparisons, joins, and groups by (less secure).
Randomized: More secure but doesn’t support joins or filtering.
⚠️ Choose wisely — you cannot change this later without re-encrypting.
🔹 Step 4: Column Assessment
The system will validate the selected column.
The wizard validates column compatibility, permissions, and dependencies.
Review any warnings (e.g., if a column is used in a computed column or constraint).
If the collation of the column is different from _BIN2, the system will prompt to change from existing to _BIN2.
🔹 Step 5: Choose or Generate a Column Master Key (CMK)
The system will display an option to select the column master key. In this section, either we can create a new column master key, or we can choose the existing column master key from the drop-down.
Select how you’ll protect the encryption key:
Windows Certificate Store (Local Machine or Current User)
Azure Key Vault (if integrated)
✅ You can:
Use an existing CMK
Or click “Generate a new key”, then provide a friendly name and description.
🔒 SQL Server will also create a Column Encryption Key (CEK) that uses the CMK.
🔹 Step 6: In-Place Encryption Settings
In the next screen, it’ll display In-Place Encryption Settings:
🔹 Step 7: Run Settings
Now, we need to select the Encryption Method:
It may be offline or online. The default value is offline.
✅ Encryption Mode:
Choose how data should be encrypted:
Run Now: Apply Encryption immediately.
Generate PowerShell Script: Save the script for manual or automated deployment at a later time.
🔹 Step 8: Summary of the Setup
In this section, wizard will show summary of the setup:
🔹 Step 9: Finish & Monitor Progress
Click Finish.
The wizard encrypts the selected columns and creates CMK and CEK objects in the database.
You can monitor the process in the wizard window or via the SSMS Messages tab.
🔹 Step 10: Completion Screen
🔹 Step 11: Verify Encryption
In Object Explorer:
Expand Security ➤ Always Encrypted Keys in the database.
You’ll see:
Column Master Keys
Column Encryption Keys
🔹 Step 12: Run a SELECT query to test encrypted columns.
Use SELECT query to test encrypted columns:
SELECT * FROM [dbo].[Citzens]
📌 Important Considerations
Important considerations are given below for more clarity:
| Aspect | Details |
| Supported Data Types | varchar, datetime, int, nvarchar, char, bit, decimal, etc. |
| Backup and Restore | CMK must be backed up separately (especially if stored in Windows cert store) |
| Impact on Performance | Encrypted columns cannot be indexed for range searches |
| Unsupported Features | Computed columns, Full-text indexes, Foreign key constraints |
| Not Supported on Standard Edition | Only available in SQL Server Enterprise Edition |
💡 Examples of Always Encrypted in T-SQL
Example 1: Insert Encrypted Data
INSERT INTO [dbo].[Citzens]([FirstName], [CitzenSSN])
VALUES ('Sandeep Diwakar', '123-45-6789');(Ensure your SSMS/driver supports Always Encrypted)
Example 2: Retrieve Encrypted Data
SELECT [CitzenSSN] FROM [dbo].[Citzens] WHERE [CitzenSSN] = 1;Example 3: Update Encrypted Column
UPDATE [dbo].[Citzens]SET [CitzenSSN] = '923-900-9999' WHERE [CitzenSSN] = 1;Example 4: How to drop CEK/CMK
DROP COLUMN ENCRYPTION KEY CEK_EmployeeSSN;
DROP COLUMN MASTER KEY CMK_EmployeeCert;📋 Conclusion
Another feature of the Microsoft SQL Server is that it is always encrypted, which is a strong, safe, and easy-to-implement data protection technique. It is designed to help protect our data in response to modern security demands. While it introduces some limitations in query and performance, its robust encryption model provides the highest assurance for safeguarding sensitive data. Business regulatory compliance and a strong data regime can be ensured by implementing the best practices for the “Always Encrypted” facilities in the SQL server and understanding its configuration and use.
🧠 FAQs – Top 50 Interview Questions
The top 50 important interview questions with answers to help you:
Q: What is Always Encrypted?
Ans: A feature in SQL Server that ensures valuable & sensitive data is encrypted both at rest and in transit.
Q: When was Always Encrypted introduced?
Ans: In SQL Server 2016.
Q: Can DBAs view Always Encrypted data?
Ans: No, unless they have access to the decryption keys.
Q: What are the types of encryption in Always Encrypted?
Ans: Deterministic and Randomized.
Q: Which T-SQL command creates a Column Master Key (CMK)?
Ans: CREATE COLUMN MASTER KEY.
Q: What is a Column Encryption Key (CEK)?
Ans: A key used to encrypt specific database columns.
Can we index encrypted columns?
Ans: Yes, if the column is encrypted using deterministic encryption.
What does a Column Master Key do?
Ans: It encrypts the Column Encryption Key.
Q: Is this feature supported in Azure SQL?
Ans: Yes, it is supported.
Q: What are Secure Enclaves?
Ans: Hardware-based trusted execution environments for enhanced querying on encrypted data.
Q: Can LIKE operations be performed on encrypted columns?
Ans: No, unless Secure Enclaves are used.
Q: Where are encryption keys stored?
Ans: Typically in Windows Certificate Store or Azure Key Vault.
Q: Can “Always Encrypted” be applied to existing columns?
Ans: Yes, but it requires data migration or redefinition.
Q: What is the difference between Deterministic and Randomized encryption?
Ans: Deterministic always produces the same ciphertext for the same plaintext; randomized does not.
Q: Which operations are allowed on encrypted columns?
Ans: Equality comparisons (deterministic only), inserts, updates, and deletes.
Q: What tools support Always Encrypted?
Ans: SSMS, .NET Framework 4.6+, ADO.NET, and Azure Data Studio.
Q: Is it possible to perform range queries on encrypted columns?
Ans: Only with Secure Enclaves.
Q: How are encryption keys protected?
Ans: With key stores like Azure Key Vault or certificates.
Q: Can you change the encryption type after applying Always Encrypted?
Ans: No, you must drop and recreate the column or table.
Q: What permissions are needed to create a CMK?
Ans: ALTER ANY COLUMN MASTER KEY and CONTROL on the database.
Q: What happens if a key is lost?
Ans: Data encrypted with that key cannot be decrypted.
Q: Can Always Encrypted be combined with TDE?
Ans: Yes, for layered encryption.
Q: Is Always Encrypted a replacement for TDE?
Ans: No, they serve different purposes.
Q: Can SQL Server functions be used on encrypted columns?
Ans: No, most built-in functions are not supported.
Q: How is client-side encryption implemented?
Ans: Through client drivers that support Always Encrypted.
Q: What does the ENCRYPT WITH clause do?
Ans: Specifies encryption properties for a column in a table definition.
Q: Can foreign key constraints be used on encrypted columns?
Ans: No, they are not supported.
Q: Can ORDER BY be used on encrypted columns?
Ans: Only if Secure Enclaves are configured.
Q: What is the default encryption algorithm?
Ans: AEAD_AES_256_CBC_HMAC_SHA_256.
Q: Can join be performed on encrypted columns?
Ans: Yes, if deterministic encryption is used.
Q: How do you rotate encryption keys?
Ans: Create new CEK and re-encrypt data using ALTER TABLE commands.
Q: Are backups encrypted with Always Encrypted?
Ans: No, Always Encrypted protects data, not backups.
Q: What driver version supports Always Encrypted?
Ans: ADO.NET 4.6+, ODBC 13+, JDBC 6.0+.
Q: Does Always Encrypted support NULL values?
Ans: Yes.
Q: How do I verify if Always Encrypted is enabled?
Ans: Check column properties in SSMS or query sys. Columns.
Q: Can you decrypt data on the server side?
Ans: No, unless Secure Enclaves are used.
Q: How do you troubleshoot the ‘Invalid column encryption key’?
Ans: Check if the CEK is accessible and correctly mapped.
Q: What collation should be used for encrypted CHAR data?
Ans: Latin1_General_BIN2.
Q: What are typical use cases for Always Encrypted?
Ans: PII, financial data, healthcare data.
Q: Is Always Encrypted compatible with Replication?
Ans: Limited support; works with snapshot replication only.
Q: Can I export CMKs?
Ans: Yes, from the certificate store using certutil or PowerShell.
Q: Can Always Encrypted be turned off?
Ans: Yes, by altering the column to remove encryption.
Q: Can you encrypt XML or JSON columns?
Ans: Not directly; serialize and store as NVARCHAR first.
Q: Can I use Entity Framework with Always Encrypted?
Ans: Yes, with supported drivers and configuration.
Q: What version of SSMS supports Always Encrypted?
Ans: SSMS 17 and above.
Q: How do you create an encrypted column using SSMS?
Ans: Use table designer or T-SQL with ENCRYPTED WITH clause.
Q: Is Always Encrypted suitable for all columns?
Ans: No, only for sensitive, query-light columns.
Q: Does Always Encrypted support indexing?
Ans: Yes, for deterministic encryption only.
Q: Can I log access to encrypted data?
Ans: Yes, using SQL Server Audit or Extended Events.
Q: Can a user without key access read encrypted data?
Ans: No, the client must have the key to decrypt.
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