Password Generation Security
How to make
passwords that are hard to crack..
All About Making Secure Passwords...
Researched by Pacific Websites
PART I:
By B. Rich: I recently read an interesting
article about the pitfalls involved in choosing a secure password. Since
it's a techie issue and something many people should be aware of (but
aren't), I thought I should recount some of the tips and background on
passwords, password selection, and how your password might be
compromised. More importantly, I'd like to show you how the weakest link
in any security structure is often the human link, and how you can
maximize the security integrity of your home or office environment just
by choosing more effective, harder to crack passwords.
Password Storage
Passwords, on just about every system, are stored
encrypted. The two general approaches to encryption are one-way and
two-way encryption. One-way encryption is a method in which characters
are encrypted so that the final outcome looks nothing like the original
plaintext, and cannot be traced back or unencrypted - the algorithm
cannot be reversed. Two-way is really more the type you hear about in
spy movies, in which plaintext is translated into gibberish using a
cipher, but can be translated back again using a special anti-cipher or
key.
Passwords that are highly important - such as the root password to a
multi-user system (your Linux 'root' password, your Windows
'administrator' password, etc.), or for most Internet mail accounts and
shopping accounts - are stored using one-way encryption. This ensures
that no matter where it is - even when it's on the system where no one
should, in naive theory, be able to get - the password is never in a
form in which it can be easily compromised. When your password is
entered (for instance, when you login to your mail or your computer),
the characters you enter in plaintext are encrypted using the one-way
algorithm, and then the final result is compared to the stored 'hash,'
the encrypted information. Only if they match will you be allowed in,
not if they are simply the same password (since no one but the user and
the algorithm knows what the actual password is).
One-way systems are then of course more secure, since, failing a
breakthrough in large number theory, it is completely impossible to
trace the original plaintext from the resulting hash using any sort of
magical algorithm. Two techniques are used in password "retrieval" (i.e.
cracking your root password when you've been silly enough to forget it
1); that is, when we're
talking about a password that can't be simply 'un-ciphered,' as by some
clever WWII Bletchley Park operative "mathemagically."
RoboForm remembers your
passwords.
http://www.roboform.com
Password Cracking
These two techniques are known as 'brute-force' and
'dictionary' attack techniques. Both have their advantages and
disadvantages, but both try to accomplish, in one way or another, the
key goal when cracking one-way encryption - to reduce the monumental
search-space for the plaintext password (your password), which, when
encrypted using the one-way algorithm, will produce the stored hash.
Now indeed, some things might have become apparent. We want to crack
let's say, an 8character password, because we happen to remember our
root password was 8 letters, just not what it was. Let's assume we've
used ASCII characters in our password (a-z, 0-9, !-?), which makes our
search-space a whopping 256^8 possible passwords - but wait! Out of the
256 ASCII characters, the first 32 are non-displayable control codes
(like beep, end-of-file, etc.) and the last 128 are 'extended' codes,
like phi, the degrees sign, and DOS graphics corner brackets - thus,
only 96 are really useable for password characters (in general) and
finally, out of these 96, the DEL code is non-displayable again, so it's
95.
95^8 (2)
is still, however, 66,342,000,000,000,000,000, which I hardly need to
point out is gargantuan. To reduce this search space - which, with a
computer capable of 1,000,000 password combination trials a second,
would take 210 processing years to crack - more action is taken to
increase the likelihood the desired solution will be found early in the
exercise (3 days) instead of late (182 years).
This is accomplished in a variety of ways. We can prune the possible
combinations by reducing the search-space, and that means using fewer
characters in the search, or less password length. Many password
retrieval programs allow you to enter wildcards (masking parts of the
password you've forgotten - 'oh I know it starts with an m but I've
forgotten the rest'). We can also make assumptions about the user's
intelligence and inventiveness to reduce the possible character set -
for instance, it's more likely a password has been constructed out of
letters and numbers than it is it's been constructed out of letters,
numbers, $'s, #'s, and %'s. Of these, it's more likely # and $ have been
used that &, ^ and @, in general (this is not ironclad from statistics,
but a good example). This can reduce the possible characters used from
95 down to anything as low as 26 (for people stupid enough to use only
one set of letters), or 68 at a slightly more encompassing list size
(including most symbols, upper and lower-case letters, and numbers).
Lastly, we can push more likely possibilities to the front of the queue
so we increase our chances of reaching a solution faster - rather than
doing a systematic search through the ASCII table, we can arrange
letters ahead of numbers, numbers ahead of symbols, common letters ahead
of less common letters, common symbols ahead of less common symbols,
etc. With all this in mind - and with the fact that most people are lazy
or unaware of password dynamics - most passwords can be cracked in under
a week on a fast computer.
In any case, however, the more preferred method of attack is a
polymorphic one, or a technique that second-guesses rather than dumbly
applies near infinite lists of character combinations. For instance:
trying English words; generating English-like possibilities; accounting
for the clever l33t substitutions which their creators may believe makes
their password 'not in the dictionary' and therefore 'uncrackable' -
most of these comprise the 'dictionary' attack.
Put simply, most people do not make their passwords {^%F^&*# - they make
them things like 'firefly' and 'swordfish' and possibly such ingenious
non-words like 'blern' and 'st00pa' which all basically fall under the
crushing wheels of a dictionary attack. No doubt, early dictionary
attack crackers were literally the Aspell dictionary attached to a
password checker, so that ubiquitous English words that people thought
'No one could ever possibly guess I would choose, hah ha!' could be
entered ahead of 6,000 processing-years of random ASCII strings.
More advanced dictionary crackers use words which have been grabbed from
web pages, articles, popular usage, movie scripts, etc. and so,
therefore, homer simpson or crantastic, though both long and not in any
dictionary, are potentially unsafe. Finally there is polymorphism and
substitution, as stated above, which will give a list of tweaked words
with common substitutions, or the ultimate in linguistico-hackery, a
random English-sounding element generator (after all, even if you have
been clever enough to enter something combining upper and lower case,
numbers and symbols, and with a good length, if it still equates to
crantastic, then it can be guessed by a program with knowledge of the
rules of English phonetics and l33t substitutions) - though this is a
challenge to say the least, some programs - notably many password
generators - are capable of similar things already.
As a final sweetener, passwords can be guessed based on previously
guessed passwords. As capitalized upon in the near-movie 'Hackers',
while passwords can be, theoretically, combinatorial nightmares to
guess, practically, they are often peerlessly simple: and thanks again
to laziness, easily crackable passwords are replicated in many systems:
PHREAK:
Alright, what are the three most commonly used passwords?
JOEY:
Love, secret, and uh, sex. But not in that order, necessarily, right?
CEREAL:
Yeah but don't forget God. System operators love to use God. It's that
whole male ego thing.
Many dictionary attack programs, upon finding a
password, put it at the top of their dictionary file, since there is a
good chance that someone else will have the same password (or a l33t
variation).
Footnotes
Footnote 1 Hopefully not for
cracking someone else's root password. Not that you wouldn't have to
have reasonably formidable skills to acquire the hash file first in
order to crack it, and therefore, it is hoped, sufficient balls and
sense of responsibility as a hacker to not do something immoral like
that.
Footnote 2 The number of possible 8-character strings
that can be made from 95 characters, not excluding repetition of
characters in the string, etc. Notably, this is different from 95 Perm
8, which is a view of 8 characters from a possible space of all
permutations of 95 characters - a subtle difference, but the answer is
out by several trillion trillion trillion so it's worth noting that
permutations should not be used to solve possible password combo
problems like this one.
RoboForm remembers your
passwords.
http://www.roboform.com
PART II
Protecting Yourself - How to Choose Secure
Passwords
In Part One of Password Infomania, Benjamin Rich discussed ways
crackers figure out passwords. In today's installation, he covers hints
on selecting good passwords that are difficult to guess or crack.
Length: Unlike baboons but similar to elephants, length is crucial. A
4-character password, no matter how clever, only has about 81 million
possibilities, a pathetically small search-space for a Pentium-level
processor to move through. Even with every possible practical
ASCII combination, covered in no particular
order, a 4-character password can be cracked by a brute force program on
our aforementioned 1,000,000 password/sec machine in just over a minute
twenty. Most machines aren't capable of this kind of speed, but even at
a thousandth of the speed, this can be accomplished in just under 24
hours.
Complexity: Sometimes called entropy. Making your password as
free of plausible patterns as possible can indeed bring it closer to 'uncrackable'.
Obviously, a 16-letter password, fridge explosion can be quickly sorted
out with a dictionary attack. Even fr1dge expl0sion, as explained, can
also be accounted for in most dictionary attacks. Therefore, a password
that increases the theoretical search-space to the largest possible,
with the fewest recognizable patterns, is best. 5-character passwords
are fairly easily cracked, although Q+f@~ is still infinitely better
than h4ppy (not that you should use a 5-character password, but your see
what I mean).
Apathy: Don't choose a password close to your heart - remember,
any cracker, or worse, someone who wants to do you real harm and has
real surveillance expertise and equipment, is going to find it much
easier to crack your password if they don't even have to use a program
to do it. If it's 11 characters long, but also happens to be your
girlfriend's or boyfriend's name, it will be on the list of first
choices for anyone seriously wanting to get into any of your systems.
We've already gone through the pitfalls of using real words or names, or
even 'non' words like those from the popular vernacular, or from
l33t-sp34k substitution, but add to this list: your birthday; your
partner's birthday; your car's number plate; foreign words; famous
phrases; pet-names; Social Security number; etc.
Remember - as typified by numerous security breaches in supposed
'impervious' systems, the weakest link is always the human one. It means
nothing if the main projects repository server of your company is secure
to thousands of outside attacks if it has a 5-letter root password which
is the name of the CEO's dog, whom he or she tells their niece in the
advertising department 'in case of emergency'. Likewise, it means
nothing if your password is easily accessible, guessable, or findable
(as in written down somewhere) even if it happens to be long and have
reasonable entropy.
Uniqueness:A highly common pitfall is to use the same password
for many things: your email, your Linux root, your eBay account, etc.
For the love of christ, don't do this: a clever password it may be, and
36 characters long, plus alphanumeric and memorized, but if you're using
it for your Joe-Blow JavaScript-R-Us online email account, and it's
stored in plaintext in a MySQL database with no password prompt hidden
on the site under the directory 'secret'... and you also used it as your
Linux root... you're in an extremely dangerous position indeed. Your
password may be a secure one, but the different agencies protecting it
may not all be secure. Using one password for everything means that
a) you're done for - repetition is the sort of thing an immoral cracker
will try first upon cracking your online email and finding your use-all
password, email-address and geographical location in plain text, and b)
you've wasted a good password because you'll have to change it to n
different other passwords on all your systems - and this is
assuming you figure out someone has your password before said
password has been used to break into and gain control of all your
protected systems.
Memorability: If you can't remember it, you'll have to write it
down, and that's inefficient and means it can be found by immoral
others. Mind you, good password practices really should be the
cornerstone of computer usage, not necessarily called into question for
their practicality - as a Linux user for example, it's unlikely anyone
will even attempt to crack your system because most immoral people use
Windows (I'm not joking on this one) - and at that, broadband users are
more at risk than dialup users, since broadband is a valuable commodity
and is more 'prominent' as it were, on the network due to a permanent or
long-standing IP1.
RoboForm remembers your
passwords.
http://www.roboform.com
Sure, sure, you're just a PC owner - unobtrusive, and you don't have the
same 3-letter password for your email as your root access - so,
theoretically, having a password less than 19 characters, or writing it
on the inside of your sleeve cuff just in case, or even telling it to a
trusted friend, aren't necessarily security-compromising activities
which will see your credit card stolen and your family dead within the
week. Nonetheless, it helps if your password is a good one, a long one,
and also something you don't have to record anywhere except your memory
- just as you take precautions in other areas of your life regardless of
the likelihood of extreme misfortune.
Generating a Good Password
Inconvenient as it is, a good password must be long; have a good
combination of upper and lowercase letters, symbols, and numbers; and
use as many twists and turns as possible. An example of a highly secure
password might be:
C#e%4/*W1
9 letters long, utilizing letters, numbers and symbols, and being more
or less uncrackable with dictionary means. Resist the temptation also of
'disguising' words with obfuscation - as stated, an English word, even
made entirely out of symbols and numbers, can still possibly be guessed
by an advanced dictionary attacker.
A good way to choose and remember a complex password is to generate the
password using a random exercise, and then type it many times to
remember it. Remember, then, the position of the keys you type; the
pattern of your fingers moving across the keyboard - not a particular
word or phrase, which is easily remembered but also easily cracked.
Generating a good password can be as simple as finding a list of ASCII
characters, and then rolling a pair of dice several times to pick out
the ones you want - a good example for this sort of thing can be found
at http://world.std.com/~reinhold/diceware.html; another way, and a much
more trodden path, is using a password generation program. Password
generating programs are mostly found for *nix environments, but there
are some for Windows, and I've included a list of useful links below -
remember to use a program that generates random ASCII gibberish, not
combinations of words or English elements. Always be on the lookout for
password generating programs that only have fixed character sets (only
letters and numbers, which alone doesn't generate enough entropy for a
password) or only English-like generations (if it can be generated, it
can be second-guessed by a dictionary attacker program).
Good Security Practices
Finally, and this is perhaps hardest of all, remember to change your
passwords fairly regularly. With highly complex passwords like the one
above, stored on a secure system, there is little need for the average
unobtrusive user to change their password very regularly - but as a
necessary habit for maintaining a secure system, it should be noted, and
particularly by those who do work in high-risk areas.
If anything can be said for good security practices, it's the reminder
that what really makes a system secure is diligence, vigilance, and
knowledge - a strong human factor. All the high-priced software in the
world will not save your company server from attack if it's system
administrator is inexperienced, unobservant, and lax in practice; the
best system is still not impenetrable if it has an obvious password - no
matter how cosseted away that password is.
RoboForm remembers your
passwords.
http://www.roboform.com
Good Random Password Generators:
Windows
Password Generator
http://www.winguides.com/security/password.php
Java Password Generator
http://www.multicians.org/thvv/gpw.html
Automated Password Generator
http://www.adel.nursat.kz/apg/index.shtml
Linux
Keymaker v1.0
Online
LoTekk Password Generator
Footnotes
1 dialup providers change their users' IP addresses
each time the user logs on - but cable providers usually give their
users permanent IPs, or IPs which have 'leases' of several months. This
means that, since your address is unchanging and constantly present on
the internet for months at a time, or forever, an attacker could
theoretically track you, suss you out, and come back later at any time
to collect.
Originally written by Benjamin Rich, Web master of
CSD.
RoboForm remembers your passwords.
http://www.roboform.com
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