Encryption algorithms in most popular programs (Word, Excel, Wordperfect, PK-ZIP, and so on) are usually very weak, even though the manual often claims that you will never be able to get at the document without the password.
Although this is mostly due to the American ITAR export restrictions (which state that programs implementing strong encryption may not be exported from the USA), you should not rely on any program for which the algorithm is not publicly available. Many of the popular ciphers are very insecure, and rely on the fact that the details of the cipher are unknown, which can have devastating effects if someone discovers the trick.
Below you will find links to cracking programs for the most popular commercial or shareware programs.
PK-ZIP, the most popular compression utility for the PC. Three programs are available to recover the
key used to encrypt ZIP archives: PKZip Cracker, ZIP Crack, and Fast Zipcrack. A more general site dealing with PKZIP is also available.
Microsoft Word also has a built-in encryption feature. A cracker is available.
Wordperfect's encryption scheme isn't very secure either. There are two crackers (one for version 4.2 and one for later versions).
Unix password cracking programs are available from CERT.
Pretty Good Privacy is a file encryption program which is generally considered unbreakable. It is used extensively on the Internet, available for almost every platform and is required for anonymous remailers. It can also create digital signatures, which makes it easy to detect forgeries.
Disk encryption programs are available to encrypt the contents of your entire hard disk. Even if you never forget to re-encrypt and wipe every file after use, editors and other programs may leave temporary files behind. If you encrypt the whole hard disk at once (similar to how Stacker or DriveSpace compress it), you don't have to worry about that anymore.
