Try standard defaults like 123 , password , or the URL of the website where you found the file.
Note that older versions (v0.41.3r is a legacy early-access build) can sometimes be accessed officially via the Betas tab in Steam properties if you own the game. Against.the.Storm.v0.41.3r.rar
For versioned game files like Against.the.Storm.v0.41.3r.rar , extraction passwords are often provided at the original download source, such as a forum or a direct download site. If you do not have the password, you can try these common steps: Try standard defaults like 123 , password ,