Choosing the Right Encryption Technology for Azure SQL Database or SQL Server

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Choosing the Right Encryption Technology for Azure SQL Database or SQL Server

Transparent Data Encryption vs. Always Encrypted

When it comes to securing data in SQL Server and Azure SQL Database, encryption plays a crucial role. Two prominent encryption technologies available are Transparent Data Encryption (TDE) and Always Encrypted. Understanding their differences and use cases will help you choose the right technology or combination of technologies for your needs. This blog provides a detailed comparison to guide your decision-making process.

Transparent Data Encryption (TDE)

What is TDE?

Transparent Data Encryption (TDE) is designed to protect data at rest by encrypting the entire database. This includes data files, log files, and backups. TDE is particularly effective against scenarios where raw files or backups might be exposed, such as in cases of data center theft or unsecured disposal of storage media.

How Does TDE Work?

TDE employs the AES encryption algorithm to encrypt the entire database. The encryption process is transparent to applications and requires no changes to existing code. TDE operates at the storage level, performing Realtime I/O encryption and decryption. Once data is loaded into memory, it is accessible to database administrators (DBAs) and applications with the appropriate permissions.

Key Management Options

TDE provides two options for key management:

Service Managed Keys: Managed by the database service and stored in the master database.

Customer Managed Keys: Managed by the customer and stored in an external key store, such as Azure Key Vault.

When using customer managed keys, the TDE protector never leaves the key vault. Azure SQL Database needs to access the key vault to decrypt and encrypt the Database Encryption Key (DEK) used for data encryption.

Best Practices and Considerations

TDE is essential for meeting compliance requirements and protecting data at rest. However, it only protects data at the storage level. Additional layers of protection, such as operating system file system encryption and hardware security measures like BitLocker, should also be considered.

 

Always Encrypted

What is Always Encrypted?

Always Encrypted is a feature designed to protect sensitive data from access by database administrators, system administrators, and even the database engine itself. It uses client side encryption to ensure that data remains encrypted both in transit and at rest, protecting it from potential threats, including compromised database servers.

How Does Always Encrypted Work?

With Always Encrypted, cryptographic operations are performed on the client side. Data is encrypted before it is sent to the database and decrypted after it is retrieved. The encryption keys used in this process are never exposed to the database engine, which means that even high privilege users cannot access the plaintext data.

Types of Keys

Column Encryption Keys: These are used to encrypt the data stored in the database. They are stored in an encrypted form within the database.

Column Master Keys: These encrypt the column encryption keys and are stored in external key stores such as Azure Key Vault or Windows Certificate Store. Only the client application can access these keys.

Advantages of Always Encrypted

Always Encrypted provides unique security benefits by protecting data “in use,” i.e., during computations and in memory. It separates data ownership from database administration, allowing for secure storage in cloud environments and reducing the need for high security clearances for DBAs.

Considerations

While Always Encrypted ensures strong protection for sensitive data, it is partially transparent to applications. Changes to the application may be necessary to support Always Encrypted’ s encryption and decryption processes. Moreover, it supports only limited operations on encrypted columns.

Combining TDE and Always Encrypted

For comprehensive data protection, consider using TDE, Always Encrypted, and Transport Layer Security (TLS) together:

TDE serves as the first line of defence by encrypting the entire database at rest.

TLS protects data in transit between the client and the database.

Always Encrypted safeguards highly sensitive data from high privilege users and potential malware within the database environment.

Conclusion

Choosing between Transparent Data Encryption (TDE) and Always Encrypted depends on your specific security needs. TDE is excellent for protecting data at rest and meeting compliance requirements, while Always Encrypted provides an additional layer of security for highly sensitive data by protecting it even in memory. For optimal protection, consider implementing both TDE and Always Encrypted, alongside TLS for data in transit. By combining these technologies, you can create a robust, multi-layered security strategy that addresses various threat scenarios.

Thank you for taking the time to read this blog post!

 


BHARATH KUMAR S

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