6.5 Backup Products
There are many commercial offerings that provide backup service. Here are some of the more interesting ones. Ultimately, you should try several of them out for yourself before deciding on one. A great list of companies that provide backup can be found at http://uk.dir.yahoo.com/business_and_economy/business_to_business/computers/services/backup/ . Many of these have a security component to them. You can use the information in this chapter to help evaluate the level of security that they offer. Keep in mind that just because a company says that they use triple DES to encrypt does not mean that their product is secure. Here is a list of questions to ask yourself before choosing a product:
Does this product compress and encrypt locally before transmission?
What encryption algorithms are used?
Do they also perform data authentication? If so, what authentication algorithm is used?
How are keys derived?
Is there a secure channel between my computer and the server?
Are file names protected, as well?
What is the key granularity?
Does the server super-encrypt?
How easy is it to restore files?
Is there user authentication for storage and recovery?
What is the user interface for backup and recovery?
Is there any reason I should trust this vendor?
Do they use well-known published algorithms and protocols, or their own proprietary ones?
How are the keys stored?
Keep in mind that almost all network backup systems require you to install client software. Installing client software over the Internet and even from a CD-ROM is a sensitive operation. It is a point at which an adversary could install a virus, or worm, or Trojan horse on your machine. By installing a native application, in a sense, you are completely trusting the distributor with your computer. While a product may claim to encrypt before sending a file, you have no guarantee that the product isn't also shipping the key in some covert manner (say, encrypted with a key that only the vendor knows) back to the vendor.
Also, even if the software vendor is totally reliable, there is no guarantee that their site has not been hacked. There are public domain tools for inserting a virus or any other malicious code into an existing application. A favorite is a program called infect, which asks for a filename to infect and the name of a malicious program, and then installs the malicious program in the target executable. I saw a demo of this. It's pretty scary.
With that in mind, here is a summary of the products. As you can see, the amount of information I was able to collect about these products from their literature and from contacting the companies for technical explanations varies widely.
This product has one of the nicer user interfaces. You can simply right-click on a file and you have the option to back it up. You can also restore different versions of a file based on the date it was backed up. All of the files are encrypted using a single key derived from a user passphrase. There is no claim that the product provides authentication in addition to encryption. The product encrypts files locally and then super-encrypts them on the server with the vendor's key. The product is pricier than most, costing $99 per year for 100 megabytes at the time of this writing. The URL is http://www.backup.com/.
This product has a similar interface to the previous one, that is, using an Explorer-like interface to determine which files to back up. There is an automated unattended backup facility available. The user has the option of using DES, 3-DES, or Blowfish. The encryption key is derived from a user passphrase, and there appears to be no data authentication. One nice feature is that there is a separate user authentication stage for storage and recovery, so users need to remember a passphrase for the key and a user password to authenticate. The product also sets up an encrypted channel to the server before any communication takes place. In addition to encrypting the data, this product also encrypts the file names for additional privacy. The URL is http://www.BitSTOR.com.
6.5.3 Secure Backup Systems
It is not clear how this product encrypts or how keys are chosen. The program compresses and then encrypts data that needs to be backed up, and it is stored in a physically protected offsite vault. The product automatically scans for changed files within a selected area of the file system and marks data for backup.
This is a product that was designed specifically for the Macintosh. However, there is nothing in the protocol that is specific to the Mac. It provides for remote backup and restore over an insecure network. Users receive the first 100 megabytes for free, as of this writing. The product uses a passphrase-derived key and performs CAST encryption with a 128-bit key and MD5 for authentication. The URL is http://www.backjack.com/.
This product is another remote backup-and-restore product. Files are compressed and encrypted locally with 3-DES using a passphrase-derived key. There is a facility for scheduling unattended backups. The URL is http://www.datalock.com/.
6.5.6 NetMass SystemSafe
In this remote backup-and-restore system, users are given a choice of 40-or 56-bit DES, or 3-DES, and keys are derived from a passphrase. There is a nice graphical user interface for administering the backups. An interesting feature of this system is that it can back up partial files by only backing up the disk blocks that have changed since the last backup. The URL is http://www.systemrestore.com/.
This remote backup-and-restore program performs user authentication via an ID and a PIN. The product tries to obtain security by obscurity (deplored by the security community). It implements a proprietary communication protocol with variable-length packets and proprietary compression to achieve "security." It has an additional property of performing virus checking on the client side before copying the backup files to the server. There is no mention of encryption or keysproprietary compression seems to be used for that purpose. This goes against all of the conventional wisdom in the security community. The URL is http://www.trgcomm.com/.
6.5.8 Safeguard Interactive
This product uses a user-supplied passphrase to derive a key used for DES encryption. Files are backed up and restored over a network. The URL is http://www.sgii.com/.
6.5.9 Veritas Telebackup
In this product, authentication of files is done using a cyclic redundancy check (CRC) instead of a cryptographic hash. This is not good practice. There is an authentication code stored in the client software to validate a session. This is also the wrong way to do it. Not only are sessions not encrypted, but anyone who ever gets access to the software can then spoof a session. There are a lot of obscurity games in this product such as variable-length packets, proprietary compression in place of encryption, and randomized storage of files on the server. None of these things would hold up against a serious attacker. Why not just encrypt and MAC the data, authenticate users, and derive 3-DES keys from passphrases? Everybody else seems to understand this to some degree. If you are curious, the URL is http://www.veritas.com/us/products/telebackup/.