Well, idk, i just figured 8 characters would be fine. And as for bruteing it... its not possible to... if you put in the right or wrong password, itll still decrypt it, so unless you can make a program to go thro all the combos, and then check to see if the file has been decrypted correctly, bruting it wont work.
What it does is goes character by character (stepping by the speed, the speed can be from 1-1024, as long as the number between 1-1024 can be mod by the size of the file), and each character it comes to, goes thro each character in the password, converts that character into ascii, and converts the character in the file into ascii, then Xors the ascii from the character in the file by the ascii in the character of the code. So, if u use an 8 character code, itll Xor each character in the file 8 times. So, when u decrypt it, it does the exact same thing.
Incase you dont know what Xor is, ill explain it real quik.
12 xor 6 = 10
how?
00001100 = 12 in binary
00000110 = 6 in binary
so, match coorsponding columns, and if the numbers are the same, then the resultant = 0, if not, the resultant = 1, so the end result would be:
00001010, or 10 in binary.