Acho que a única maneira de testar é o método Bruteforce . Existem muitas ferramentas que podem fazer o trabalho, mas é uma solução muito ruim / longa / ...
No linux, você pode tentar Rarcrack .
Exemplo:
rarcrack archive_encrypted.ext [--threads thread_num] [--type rar|zip|7z]
De acordo com a documentação:
Everything in [] are optional, rarcrack default crack two threads and autodetect the archive type. If the detection wrong you can specify the correct file type with the type parameter. RarCrack currently crack maximum in 12 threads.
After the cracking started RarCrack will print the current status of cracking and save it's to a status file. If you want more specific password character set, you need to run RarCrack to create the XML status file (3 sec).
<?xml version="1.0" encoding="UTF-8"?>
<rarcrack>
<abc>0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ</abc>
<current>uU</current>
<good_password></good_password>
</rarcrack>
This is a sample XML file, and you see there is a character set. If you want, you can modify this file and when you start RarCrack again the program will be use new variables.
Warning: Take care when you changing this file, make sure the current password don't have characters outside the abc[character set]!