Can't reverse known hash ?

[mastercracker]

The point of a mask is telling what is the keyspace you are willing to cover. People tend to use specific patterns so instead of using bruteforce with every possible characters for every position of the password, you can specify for each position what characters to try. For example when facing the constraint of creating a password of at least 8 characters and at least one digit, they will create a password length 8 with the digit at the last position. Also most people use only lowercase so you can try:

Code:

?l?l?l?l?l?l?l?d

Try it and compare how much time it would take compared to the full keyspace bruteforce: ?a = lowercase + uppercase + symbol + numeric

Code:

?a?a?a?a?a?a?a?a

That's why we use masks: reduce keyspace while covering the most likely possibilities.