How Does the Decryption Process Work After Encryption With BitLocker?

Accessing data encrypted by BitLocker involves several steps, both from the user's perspective and within the computer's systems. Here is a detailed breakdown of the process:

1. User Initiates Access:

Action: The user attempts to access the encrypted drive, typically by double-clicking the drive icon in Windows Explorer.

Internal Process: The operating system recognizes the drive as encrypted and prompts the user for authentication.

2. Authentication:

Action: The user provides the BitLocker key, which can be a password, a smart card, or a USB drive containing the key.

Internal Process: BitLocker retrieves the key provided by the user and compares it against the stored key in the Trusted Platform Module (TPM) or on the drive itself.

3. Key Verification:

The system verifies the provided key by checking the Platform Configuration Registers (PCRs) in the TPM. The PCRs store measurements of critical system components, including the Master Boot Record (MBR) code, NTFS boot sector, NTFS boot block, boot manager, and other essential components. If any of these components have been altered, the PCR values will not match the expected values, and the system will prompt the user for a recovery key.

If the PCR values match the expected values, the TPM uses the Storage Root Key (SRK) to decrypt the Volume Master Key (VMK). The VMK is then used to decrypt the Full Volume Encryption Key (FVEK). The FVEK is the key that encrypts the actual data on the drive.

In addition, you can find more detials from this official page.

4. Decryption of the Drive:

Action: The user waits while the system processes the decryption.

Internal Process: BitLocker utilizes the FVEK to decrypt data blocks as they are accessed. This means data is decrypted on-the-fly as it is read from the drive, ensuring continuous protection while maintaining accessibility.

5. Data Access:

Action: The user can now access and interact with the decrypted data as usual.

Internal Process: The system handles read and write operations transparently, decrypting and encrypting data blocks in real-time as they are accessed or modified.

Conclusion

The entire decryption process is designed to be seamless, maintaining security without significantly impacting the user experience. By understanding these steps, users and administrators can better manage encrypted drives and ensure that data remains secure yet accessible when needed.