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ZAMYLA CHAN: All right.

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Let's get cracking.

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For this walk-through, because
this is a more comfortable problem,

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I will be going over
some of the concepts used

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to solve this problem but
less so some of the code

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that you might use to do it.

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Your tasks for this problem are to
get the hashed password from the user

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and then try to crack that password.

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The hashed password will be passed
in via a command-line argument.

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So make sure to ensure that the
user is using your program properly.

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If your program is executed without
any command-line arguments or, perhaps,

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more than one command-line
argument, then your program

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should print an error of your choice
and exit immediately with main returning

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one, thereby signifying an error.

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All right.

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Now that you have the hash,
let's try to crack this password.

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In order to reasonably
solve this problem,

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we'll allow you to make
several assumptions.

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The first of which is that
all of these passwords

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are hashed with C's
DES-based crypt function.

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Take a look at the man
page for this function.

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You'll find that crypt takes
in two arguments, key and salt.

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And you can find the salt
because it's the first two

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characters of that hashed password.

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Key to solving this problem is
remembering that hashing a word

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will always return the exact same hash.

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The crypt function is deterministic.

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So as long as you pass
in the same key and salt,

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crypt will always return the same hash.

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So I want you to try a word.

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Hash that try calling
the crypt function.

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And if those hashes match, then you
can assume that you've successfully

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cracked the password.

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More assumptions that you can make
as you're guessing these passwords.

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One, that they're no
longer than four characters

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and that they're composed entirely
of alphabetical characters.

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So how might you generate
the plain text to be hashed?

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For the guesses, think of a
way to carefully iterate over

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every combination of one to four
characters where all of the characters

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are alphabetic and case sensitive.

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Consider an array,
perhaps, of five bytes.

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And use one to four of those
bytes for alphabetical characters

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with a trailing backslash
0 to end the string.

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And also be sure to left-align
the string in the buffer.

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Calling crypt on those and
checking it against the user

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provided hash will, hopefully,
get you to crack these passwords.

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My name is the Zamyla.

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And this was crack.

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