Does the rar file format use a serious encryption (such as AES)?
Will it take unfeasibly long to brute force a password?
If not, what tools do you suggest that do so automatically?
The current version of Rar is using AES encryption with 128 bit key length.
That depends entirely on the strength of the password.
There are some shareware programs (e.g. RAR Password Cracker, RAR Password Recovery) using 'brute force' and 'dictionary-based' attacks to crack the password, the process can be very time consuming (again, depending on the password strength).
Although I don't know which mechanism exactly, RAR used pretty solid encryption. Brute force attacks on it have been known to last :), for all but the simplest of passwords.
(there were some password extacting mechanisms for old versions of rar, but I do mean oooold, ... DOS days or something from that time period).
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