I have few questions too but about rar files security.
1) Does somebody knows if is it possible to unlock a locked rar file
and change for example a file name or directory name in it without
corrupting it ?
2) Is it possible to crack a password protected (encrypted) rar file if
let say 20 to 30 characters random password was used to secure it?
If yes how long could the cracking process last on a computer grid?
1) Yes. You just gotta brute force the password with the specific software.
2) Maybe, depend on your luck as the password can be any type. Depends on the characters though. A password with 20 random letters would take a desktop PC about 157 billion years to crack it (to go through every possible value). This was tested amaturely by me on the site
howsecureismypassword.net by simply typing 20 random letters. Don't know if it's true but you can test it for yourself if you want.
Thanks.
For question under point
1) for locked file I thought of an unencrypted file
without password protection that was locked by using rar locking option only which
prevents the user from changing the content or the rar archive.
By using only this option the content is still readable or extractable without the password
but can't be altered by the user in the rar archive itself.
I tried to alter a file name in the archive by opening the archive in text editor and changing the file name
and then saving the file again.
After I have opened it again in the winrar I receved an error that the file is corrupted.
2) so actually there is no threat from a normal pc user but could it be from a corporation or government
which could have a lot of computing power?