Mention password strength online and someone will usually reference the famous XKCD password cartoon. If you haven't seen it, the idea is that the entropy of the password must be as high as possible, and that this can be adequately achieved by stapling together easily-remembered conjunctions of words
rather than difficult-to-remember strings of meaningless symbols. Some commentators have since pointed out flaws in the logic behind that cartoon.
Entropy is a head-twisting concept. Put simply, it is a measure of the chaos, disorder or unpredictability something contains. In information theory, entropy can be calculated and boils down to how many unknowns there are in a piece of data.
Consider a game of hangman. At the beginning of the game, none of the letters are known. Because there are many different possibilities, we can say that the unknown word contains high entropy. As you reveal each letter, the entropy quickly drops because of the way the English language works. Q is usually followed by U, for example, and not P or S or J. After revealing surprisingly few letters, we can usually infer the full word and win the game.
Passwords need high entropy. There should be no relationship between letters, so that if one character becomes known, it does not compromise the rest. If someone shoulder surfs you and spots you typing something like "M4nch3st" and they know you're a Manchester City or United fan from glancing at your coffee mug, then your carefully placed capital and number substitutions are all for naught.
Many people still think that strong passwords are required to protect from brute force attacks, but this is largely false. When cybercriminals want passwords, they either take them by the million using attacks such as SQL injections, or have people hand them over in phishing attacks. Because of this, we need lots of passwords to compartmentalise our lives into discrete blocks. Compromise one account and the others stay secure. Re-use them across accounts, and one key fits many locks.
There are lots of strategies for generating and remembering high entropy passwords. One successful technique is as follows:
1: Take a long line from a favourite book, play, song, nursery rhyme, whatever.
2: Take the initial letters from the words in the line and put them together.
3: Change vowels into numbers and other symbols, capitalise others.
Et voila! A long, high entropy password you cannot forget. Here's an example based on an episode of a sitcom that came to mind just now quite by chance:
In the Fawlty Towers episode The Germans, the Major says something like: "I must have been keen on her; I took her to see India!"
The 13 initials in this phrase are: imhbkohithtsi
Changing some letters to symbols and capitalising others gives: !mHbK0H1ThTsI
The online password strength meters I tried claim this password is strong or even very strong. Someone would have to know you were keen on that episode of that sitcom, guess the exact line from it, and guess exactly how you'd mangled the initials to stand a chance of recovering the generated password.
Now do that for the dozens of sites you need to log into, even those sites you intend to use very little but for which you must still set up an account. Ideally, each password must be different and unrelated. It's just not practical, is it? In fact, that sinking feeling you're probably experiencing has a name: password fatigue.
We could just store all our passwords in our browsers and create a master password to protect them. But what if we want to log in from another laptop, tablet or phone? This problem has led to the rise of the password manager.
A good password manger needs to securely store all your passwords, and to sync across all your devices. It should automatically capture the passwords you enter as it goes, and should contain some nice-to-have features. For example, the option to generate random, very high entropy passwords would be good. Intelligent form filling would also be useful.
There are other potential advantages to password managers. Because they recognise the sites you visit, if you get taken in by a phishing email and click on a link to enter your password, the manager will not recognise it, and should fail to cough up the creds. If you've allowed the manager to generate random passwords that you never see, there's no danger of you overriding it either.
I'm not going to recommend a single password manager, but you should check them out sooner rather than later. Instead I will point you to a comparison chart for you to make your own decision.
There are pros and cons to using password managers, however. Some people, like our own Simon Edwards, have argued that caution is needed. Last year, for example, cloud-based password manager LastPass was hacked and user data spilled (including security questions and encrypted passwords). Malware has also targeted local password managers such as KeepPass that do not use a cloud service.
Because of these weaknesses and attacks, passwords and password managers may not be enough. A good password manager also needs to feature 2-factor authentication. Biometric authentication would be even better as this is substantially harder to subvert.