ITPEC IP October 2020 Question 39
One of the methods of cracking a password is a brute force attack that attempts all character combinations. When the number of characters of a password that is composed of 26 letters from A through Z is increased from four (4) to six (6) characters, by what factor is the maximum number of attempts to successfully crack the password with the brute force attack increased?
Explanation
676 — every added character multiplies the number of possible passwords by 26.
With 26 possible characters in each position, a password of n characters has 26n combinations, the maximum number of brute-force attempts:
- •4 characters: 264 = 456,976
- •6 characters: 266 = 308,915,776
- •Factor: 266 ÷ 264 = 262 = 676
Answer (d)
Why not others:
- •(a) 2 — the number of added characters, 6 − 4, not the growth in combinations
- •(b) 24 — not a power of 26, so it cannot be the ratio of two counts of the form 26n
- •(c) 52 — 26 × 2: adds 26 for each extra character instead of multiplying by 26 for each
Key rule: The search space grows exponentially with length: each extra character multiplies it by the size of the character set, which is why length adds more strength than anything else.
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