[Note: I deleted my original message because most of it belonged in another thread. However, diklik already responded to part of it, so see his quote above for the relevant part of my original post. Sorry for the confusion.]
Fascinating but incorrect presumption. You can obtain RAR and ZIP cracker programs free if you search for them. I have used several in the past that open up any of those encryptions without a hassle, and without the password. If anyone can get these free, imagine what a security expert can do if they are dedicated to opening and checking files on a website...
Yes - you are right, there are many cracker programs out there. It is important to be aware of that. This is true not just for RAR/ZIP files - but every system that someone would want to break in to.
But my statement is still true: it is not possible to unencrypt the file without the password. (Without the password "key" the file is gibberish.)
Crackers work by trying to guess the password, either using a dictionary (looking for recognizable words) or "brute force" - simply trying every password combination. A dictionary attack, if successful, is reasonably fast. A brute force attack takes days, or even weeks (or longer)
depending on the length of the password. They can't get into the file until they can find the password.
Which leads to a security truism: You are only as safe as the complexity of the password. If you use words found in the dictionary in your password, anyone with some time on their hands and enough motivation can crack it. On the other hand, if you use complex passwords you are forcing the attacker to fall back on a brute force attack. Few accounts hold anything valuable enough to warrant weeks of password processing.
Moral of the story: ALWAYS use complex passwords on anything you want to protect. Make sure that they are:
- At least 15 characters in length
- Mix upper and lower case
- Use numbers and symbols
- Never use dictionary words
This doesn't have to be hard to remember. I like to use songs that are stuck in my head. Use the first letter of each word in a memorable chorus, and then add in some familiar numbers from an old address, phone number, or friend's birthday.