Ask Leo! #704 – How Do I Choose a Good Password?

This Week's Newsletter

Featured: Choosing a good password is more important than ever.

Also this week: Access Points versus Routers (fight!), and why, even with the best security you can muster, your bank account can still get hacked.


I'm still recovering from my overseas trip, but I gotta tell ya -- as listeners to an episode of the TEH Podcast will have heard me say a couple of weeks ago, I continued to be amazed by the technology along the way.

That Google Maps "just works" when I land in a completely foreign country is not only a pleasant surprise, but simply makes life so much easier as I used it extensively to navigate the countryside. (Even if it did mispronounce most of the place and street names. Smile)

I think what amazes me most, though, is that that I can be answering Ask Leo! questions at 38,000 feet (which I did), while simultaneously chatting with my cousin back in The Netherlands (ditto), and surfing the internet to see how the weather and traffic were at my destination (warm and icky, respectively). The biggest issue I had online? Remembering to pause Google Drive, OneDrive and DropBox so that they wouldn't hog the in-air bandwidth. (Typing that reminds me that I need to go un-pause them.)

These are amazing times we live in. I hope we never take it all for granted.


How Do I Choose a Good Password?


We frequently hear of major websites suffering data breaches that expose millions of user accounts and passwords to hackers.

This type of theft makes the concept of “good passwords” all that much more important to understand.

Moving target

What makes a password good constantly changes, perhaps in ways you wouldn't expect.

To understand what makes a good password, we need to understand what makes passwords vulnerable, which means understanding a couple of the ways hackers hack.

Along the way, I'll also discuss “hashes” and why a “salted hash” isn't breakfast food, but rather a critically important approach websites should be using to keep track of your passwords.

And there will be rainbows.

The rules: old and new

For those with short attention spans, I'll start with what you need to do differently, beginning yesterday.

In the past, the traditional advice on passwords was:

  • Eight characters long, minimally
  • Never use names or words, at least not without mangling them somehow
  • Never use combinations of names or words, at least not without mangling them somehow
  • Use a combination of upper and lowercase letters and digits
  • Use at least one special character — something other than a letter or digit — if the system will let you

Those rules are no longer sufficient. Even if you carefully follow them all you're left with a password that remains very susceptible to many types of compromises.


  • 12 characters long at a minimum. I recommend 16 and use 20 myself, when possible.
  • Longer is always better
  • Use a combination of upper and lowercase letters and digits
  • Words aren't quite as evil as they once were, as long as the password is long enough
  • Consider padding the password with a random character to make it even longer

As you can see, there's a new emphasis on length.

If you remember nothing else from this article, let it be this: size matters: longer is better.

The dictionary attack

One reason we were told to never use normal words (or common names) in passwords is that there are simple attacks, called “dictionary attacks”, that try all words, or all combinations of words, one after the other, until something works. Many attackers jump-start this process by starting with a list of known common passwords or words used in passwords.

The Oxford dictionary tells us:

This suggests that there are, at the very least, a quarter of a million distinct English words… 1

If we stick to a single case (upper or lower, just not mixed), then a program needs to try only 250,000 times 250,000 (62.5 billion) times to be guaranteed to stumble onto a two-word password. I say “only” 62.5 billion because to a computer running with speeds measured in billions of operations a second, that's nothing.

Yes, you can add names and random capitalization to the mix, and perhaps even insert digits, but even that slightly-obfuscated dictionary-based approach to password cracking is easily performed by today's technology.

It's also not necessary any more.

It's now quite possible for hackers to try literally everything.

The brute force attack

Let's say you've been really, really good and you have an eight-character password made up of completely random letters, numbers, and symbols.

Perhaps 7CxX&*Xf.

That's a good password — perhaps the best you can do in eight characters — but it's not a great password.

It's estimated that such a password could be cracked (offline) in a little over 18 hours.2

It doesn't matter that you didn't use words or your name or anything else. Eight characters – 6,704,780,954,517,120 possible combinations and passwords – can be hacked in less than a day.

Now, the most common response I get is, “How can they try that many that fast when I get locked out after getting it wrong three times?”

Online attacks

The attacks I've described so far all involve the hacker having a stolen copy of some user account database that they can access on their own computer(s), offline. This allows them to attempt to crack it at extremely high speed — as fast as their computers allow.

In the online scenario, actually accessing the service directly attempting to break in, they can't try nearly that fast. However, they can use other techniques to try fast enough for it to still be a serious issue.

For example, consider a botnet of hundreds of thousands of computers across the globe performing a distributed dictionary attack against a set of email accounts. Slowly, patiently, and from different locations so as not to trip any limit filters, they try millions of passwords against hundreds of thousands of accounts.

Eventually, they'll hit pay dirt — especially if they try those “most common” passwords first.

Surprisingly, that's not why eight characters is too short. A truly random eight-character password will probably protect you just fine from these types of online attacks.

It's the offline attack you need to worry about, where your eight-character password — any eight-character password — might be cracked in microseconds.

To understand how that can be, we need to understand how passwords are stored. But first we need to realize that guessing from the outside is only one way to get password information, and it's no longer the most common.

The database breach

Every so often, we hear of an online service that has been hacked into and had their database stolen.

What that usually means is that rather than trying to guess logins one at a time, a hacker has infiltrated the systems of the service and snatched a copy of some or all of the user accounts database.

As a result, they typically have:

  • A list of all usernames or login IDs for that system
  • A companion list of password information for those login IDs
  • Other stuff that the system may have stored for each user ID

No need to try guessing passwords slowly from the system's public-facing login; the hackers walk away with almost all the information they need in one fell swoop.

Note I said “password information” above. Properly secured systems don't store your password — they store something else.

Hash (hold the salt)

What a secure system stores instead of your password is called a “hash” of the password.

A hash is a mathematical function that takes an arbitrary amount of text and computes a number from it. That number has the following characteristics:

  • Any change, however small, in the data being hashed should result in a large change in the resulting hash.
  • It should never be possible to reconstruct the original data from its hash value.
  • It's not feasible to craft data that, when hashed, would generate a specific hash value.

So, instead of storing your password “iforgot”, the system might instead store:


That's the result of an “SHA 256” hashing function. Any time you give that function “iforgot,” SHA 256 will return that number (which happens to be 256 bits long).

This is important: given only the hash, there's no feasible way to figure out what password caused it to be generated. Hence, it's often called a “one way” hash.

When you log in, the system passes whatever you type as your password through the hashing function, and if the resulting number matches, then you must have typed in the correct password, because it's the only thing that could generate that number.3

Your actual password is never stored.

Unfortunately, as technology has grown more powerful, we've run into an interesting issue that puts this technique at risk anyway.

Rainbow tables

Consider the eight-character password.

If the password we choose allows each character to be any of 26 alphabetic upper and lowercase characters, 10 digits, and 10 special characters, that's 72 possible characters in each position. If we have eight of those, that's 72 to the eighth power or 722,204,136,308,736 – 722 trillion – possibilities.

It sounds like an enormity, but with today's computational and storage power, with a stolen database and an offline attack it's possible to:

  • Calculate all possible eight-character passwords
  • Calculate the hash value for every possible eight-character password
  • Store that in a massive table saved on disk

“Cracking” a password from a stolen database is just looking up the hash value you got from the database and fetching the corresponding password. This type of table is called a “rainbow table.”

In reality, hackers rarely need the entire table. People tend to pick bad passwords, so a smaller table with the hash values of lots and lots of common passwords is enough to crack a huge number of accounts.

The hashing algorithms are often quite standard.4 So, if your email service, your social media service, your photo-sharing service, and whatever else you log into all use the same hashing algorithm, they'll all store the exact same hash value for your password. If that table of password hashes is ever stolen, then a quick lookup in a rainbow table will retrieve your password. Then the hackers can try it at any of those other sites, even though they were never directly breached.

As it turns out, there's a trivial way to stop that possibility.

Add seasoning.

The Salted Hash

“Salting” is a way to obscure the information stored in a service's password database.

Instead of computing the hash of a password, they add something to the password and hash the combination. Then, when the time comes to check that you've entered the right password, they take what you've typed in, add that same something to it, and hash the result. If the hash value matches, then the password is correct.

For example, perhaps I create my password as “iforgot”. As we saw, that gave us an SHA256 hash of


If, however, the system storing my password automatically adds “mypants” to every password and hashes the result —  “iforgotmypants” — the hashed value is completely different.


When I come back to log in and enter “iforgot,” the system automatically adds “mypants”, hashes that, and the values match.

If that hash value is ever in a rainbow table somewhere, it maps to “iforgotmypants”, which is most decidedly not my password.

The item we add — in the example above, the frivolous “mypants”  — is known as “salt,” as it changes the flavor of the result of the hash function. In reality, it wouldn't be anything so simple and it would vary from system to system (and if done really well, from account to account).

Now, with all of that as backdrop, here's the kicker: you don't know how the services you use encode your password, and too many do not use salt. In fact, a recent breach at an extremely well-known large online service exposed the fact that they were not using salt at all to secure their database of hashed passwords. The stolen passwords could be easily looked up via rainbow tables.

So, in the face of not knowing which services do password security correctly, how do you protect yourself?

Size matters

The single most important thing you can do to improve your password's security is to make it longer.

The longer the better, in fact.

Recall how I said an eight-character password gave us 722 trillion possible combinations? (722,204,136,308,736, to be exact.)

A 12-character password results in 19,408,409,961,765,342,806,016 possible combinations.

There's no rainbow table big enough for that, and there won't be for quite some time. Short of storing your password unencrypted (which is a huge security no-no anyway), just about any hash will do, salted or not.

As a bonus, it's extremely unlikely a dictionary attack will bother with the assorted combinations to eventually get to whatever it is you put in 12 characters.

Length doesn't imply complexity. There's a very strong argument that says:


is, in fact, a significantly more secure password than


— plus it's easier to remember. (Although using normal words in this manner still makes me nervous for reasons I can't quite explain. Smile)

In fact, even longer passphrases — something like:

correct horse battery staple

are perhaps best of all. (With big a hat tip and propeller twirl to that great geeky web comic XKCD.)

The bottom line (this time at the bottom)

So, what should you do?

  • Abandon eight-character passwords. They should no longer be considered secure. Period.
  • Make all passwords 12 characters or longer. (You can make a password longer and more secure by adding repeating characters if you can't think of anything else.)

That's the bare minimum. For bonus points:

  • Make your passwords 16 characters or longer. I use 20 characters myself whenever possible.
  • Use a password generator, such as that included with many password vaults, to make it a 16 character or longer random password.
  • Never use the same password in more than one place. If, for some reason, an ID and password gets compromised at service “A”, hackers will then run around to many, many other services and see if they can log in with it. All too frequently, they can.
  • Consider using a password vault like LastPass to remember all your unique passwords for you.

And of course, keep your PC secure. No matter how strong your password, malware such as keyloggers can capture it, and using an open WiFi hotspot without proper security could be the moral equivalent of writing your password on the wall for all to see.

Related Links & Comments: How Do I Choose a Good Password?

Ad-Free Ask Leo!

Support Ask Leo! and enjoy an ad-free experience whenever you visit

Become a patron for as little as $2/month (or $24/year) for Ad Free Ask Leo!.



No Ads

What's the Difference Between a Router, a Wireless Router, and a Wireless Access Point?

I've searched your archives and found articles on adding a router to a router. That's the same as adding an access point, right?

No, it's not.

And it's a common enough point of confusion that I want to clarify exactly what each is and why the difference might matter.

Continue Reading: What's the Difference Between a Router, a Wireless Router, and a Wireless Access Point?

How Could My Bank Account Have Been Hacked if I Have Good Security?

My bank account was just hacked. The hacker opened a new account, transferred money from my line of credit into that account, then transferred the money out to his outside account. So, it appears he somehow got my client card number and my password.

My laptop is about five years old, running Windows 7, which I update every week. I have BitDefender for virus scans, which I do a full system scan every week. My password was 15 characters long, with a mix of numbers and upper and lowercase letters. When I am not at home, I use a VPN service while on the internet. I have changed my bank passwords to 22 characters long and installed Malwarebytes Premium for real time virus protection.

So, I have two questions: how could a hacker possibly do this with the precautions I have? and how can I protect myself further from this point?

You do have good security in place — above average, I'd say. That makes this situation a little more difficult to diagnose, as well as a tad more frustrating.

While I certainly can't tell you exactly what happened, I can speculate on some possibilities. I also have a few ideas on how I'd protect myself if I were in your shoes.

Continue Reading: How Could My Bank Account Have Been Hacked if I Have Good Security?

The Ask Leo! Tip of the Day

A feature exclusively available to Ask Leo! Patrons Bronze level & above.

More Ask Leo!

Tech Enthusiast Hour: I'm one of the regular hosts of the weekly Tech Enthusiast Hour podcast! Join us as we discuss the latest news & tech goings on. More information at!

Become a Patron
Ask Leo! Books
Facebook - YouTube - More..

Leo's Other Projects....

HeroicStories Since 1999, HeroicStories brings diverse, international voices to the world ' reminding us that people are good, that individuals and individual action matter. Stories - new and old - are published twice a week.

Not All News Is Bad - Each day I look for one story in the current news of the day with a positive bent. Just one. And I share it. - My personal blog. Part writing exercise, part ranting platform, it's where I write about anything and everything and nothing at all.

Help Ask Leo! Just forward this message, in its entirety (but without your unsubscribe link below) to your friends. Or, just point them at for their own FREE subscription!

Newsletter contents Copyright © 2018,
Leo A. Notenboom & Puget Sound Software, LLC.
Ask Leo! is a registered trademark ® of Puget Sound Software, LLC

Posted: May 15, 2018 in: 2018
« Previous post:
Next post: »

New Here?

Let me suggest my collection of best and most important articles to get you started.

Of course I strongly recommend you search the site -- there's a ton of information just waiting for you.

Finally, if you just can't find what you're looking for, ask me!

Confident Computing

Confident Computing is the weekly newsletter from Ask Leo!. Each week I give you tools, tips, tricks, answers, and solutions to help you navigate today’s complex world of technology and do so in a way that protects your privacy, your time, and your money, and even help you better connect with the people around you.

The Ask Leo! Guide to Staying Safe on the Internet – FREE Edition

Subscribe for FREE today and claim your copy of The Ask Leo! Guide to Staying Safe on the Internet – FREE Edition. Culled from the articles published on Ask Leo! this FREE downloadable PDF will help you identify the most important steps you can take to keep your computer, and yourself, safe as you navigate today’s digital landscape.

My Privacy Pledge

Leo Who?

I'm Leo Notenboom and I've been playing with computers since I took a required programming class in 1976. I spent over 18 years as a software engineer at Microsoft, and after "retiring" in 2001 I started Ask Leo! in 2003 as a place to help you find answers and become more confident using this amazing technology at our fingertips. More about Leo.