I am often asked when talking to my customers about the differences between Key Recovery and Data Recovery for encrypted files, in addition to which method to use. As a result, This Blog will focus on both areas, explaining the differences and best practices.
Both methods can easily be understood, after understanding the Encrypting File System (EFS) process in a domain environment including certificate enrollment and file encryption
When a user attempts to encrypt a file without having an EFS certificate the following process takes place:
Note: I am not a big fan of self-signed certificates especially when there are Enterprise Issuing CAs in a given Active Directory Forest. As a result, I recommend disabling the machine’s ability to generate an EFS Self-Signed certificate using the hotfix for Windows XP or Windows Server 2003
Windows Server 2008 and Windows 7 have a group policy setting which can disable the generation of an EFS Self-Signed certificate simply by unchecking the option to “Allow EFS to generate self-signed certificates when a certification authority is not available.
Once the user has a valid Encrypting File System (EFS) certificate, then they can encrypt their files and folders following this process:
For more information about EFS Encryption, refer to How EFS Works on TechNet
An organization’s security policy typically lists the following reasons for allowing data or key recovery:
Note: A difference among the reasons listed, however, is that a computer theft or loss can mean the user’s private key is compromised and, therefore, the certificate associated with the private key should be revoked. There is no reason to revoke the certificate for the other reasons in this list because the user’s private key is not compromised.
If your domain has a designated File Recovery Agent certificate enrolled, also known as the Data Recovery Agent, then the computer will retrieve its information from the local computer configuration – deployed through Group Policy – extract the Public Key from the recovery agent’s certificate, and encrypts the File Encryption Key (FEK) with it. This process will apply to all the Data Recovery Agents in the domain.
This is not a trick question; the Key Recovery Agent (KRA) certificate doesn’t come to play at all when encrypting a file a folder. Key Recovery Agent (KRA) is enrolled using the Key Recovery Agent Certificate Template, and then added to the CA configuration. The Key Recovery Agent (KRA) can extract the end user’s Encrypting File System (EFS) Private Key and Certificate from the CA’s database, which in turn can be used by the end user to decrypt their files.
When a certificate template specifies Key Archival, the private key with a certificate request must be securely transmitted from the requesting client computer to the Certification Authority for archival in the CA database. When a client requests a certificate that has Key Archival enabled, the following process takes place:
There isn’t a correct answer for this question. It all depends on your company’s policies and procedures. It is also important to note that the person or group performing Key Recovery or File Recovery should be trustworthy and held to the highest levels of scrutiny. Understanding the difference between Key Recovery and File Recovery Procedures can help you determine the correct answer to your infrastructure’s requirements.
With Key recovery. The user’s original certificate and private key are recovered from the CA database and restored to the user’s profile. Recovery of the user’s certificate and private key allows the user to access the FEK stored in the EFS-encrypted file, returning access to the file to the user.
The major advantages for Key Recovery are:
The major disadvantages of Key Recovery are:
Data recovery on the other hand, allows a designated EFS Recovery Agent to decrypt all EFS-encrypted files on a computer. By default, where the private key associated with the EFS Recovery Agent certificate exists – which can be a designated recovery computer, or the end user’s computer.
The major advantages of Data Recovery are:
The major disadvantage of Data Recovery is the recovery method itself, because the Data Recovery Agent has to decrypt the end user’s files either on premise or remotely. This can have a significant impact on data transfers from remote sites to hub sites, or vice versa because the encrypted/decrypted data has to be copied twice.
A common misconception is that the Administrator account is the Data Recovery Agent (DRA) or the Key Recovery Agent (KRA). Both recovery methods rely on the certificates (Private and Public Key Pairs) of the KRA and DRA, which means anyone who has possession of them can recover keys. If an end user manages to possess the Data Recovery keys as an example, then they can decrypt any encrypted file in the organization. As a result, you should protect these keys, and establish a chain of custody anytime the key is used.
Encrypting File System (EFS) shouldn’t be implemented without proper planning because of complexities in Data and Key Recovery. Make sure to understand both recovery methods before enrolling the first EFS certificate, and test recovery multiple times in a lab environment. Lastly, consider implementing both methods for extra recovery protection
Amer F Kamal
Senior Premier Field Engineer