How long would it take to crack AES-128 knowing a 12 character length password? I have a hard drive which was encrypted with XTS-AES 128-bit on OS X. I know how long the password is but that's it.
How long would it take to decrypt it already knowing this?
I have read that in years to come when quantum computers are available it can be broken.
Dont comment "never" or  "6 billion year" 
Think outside of the box with advancing technology in years to come.
I have memories on here.
The average 12 character password will take 6 billion years to brute-force at 100,000 passwords per second.

WolframAlpha &quot;password of 12 characters&quot;

Allowing special characters brings this to around 150 billion years.

WolframAlpha &quot;password of 12 characters&quot; with password rules

For more information, see Security.SE:

How long would it take to brute force an AES-128 protected pdf knowing the key is 20 letter long and that the charset is A-Z,0-9?