Passcodes Redux

To-day, I found myself unable to log-in to this 'blog. I got a diagnostic that I were entering the wrong password. I don't want to burden my readers with a detailed retelling, but what had actually happened was that an up-date of WordPress rejected my password — it wasn't that I were entering the wrong password; it was that the password that I was entering was now prohibitted.

On top of the login code misreporting the problem, the code for resetting the password wouldn't tell me why my password was being rejected. But it was rejected for containing a particular sub-string; and when I removed that sub-string, the password was then accepted.

If you understand passcodes (perhaps in part from reading my previous entry in which they were discussed), then you should see that there is something literally stupid in the WordPress software. Let's say that the forbidden sub-string were 8675309 and that my password were X.52341-hunao-8675309.Y. If I drop the 8675309, the password becomes X.52341-hunao-.Y. That is now accepted, though it is less secure!

If a would-be intruder knew where in the original password 8675309 appeared, and knew the length of the password, then the password would effectively be p1p2p148675309p22p23 where each pi were an unknown character, and the new password would be p1p2p14p22p23 so that the two passwords would be equally secure!. (Either way, an intruder must find a sequence of sixteen unknown characters.) But, as it is, would-be intruders wouldn't be sure that the sub-string appeared, let alone where in the code it would appear, nor how long the password were. One could, in fact, conceptualize the sub-string 8675309 as if it were a single character of extraordinary length (a macro-character) and of great popularity which character might appear within a string of equal or greater length, in which case prohibiting the sub-string would be rather like prohibiting the use of E.

That's not to say that common sub-strings should simply be accepted as passwords or within passwords. A great many systems have been hacked because someone foolishly used passwords such as password, root, or batman. But, instead of rejecting a password because it contained a popular sub-string, the software could, for example, test to see whether the password would be secure if the sub-string were excised, in which case it should be at least slightly more secure if the sub-string were retained.

(Note that this approach works with popular sub-strings of any length, including those of just one character! In fact, when there is no upper-limit on the length of passcodes, they may be securely constructed of nothing but popular sub-strings each of which has multiple characters; a secure password could be made by concatenating ten or more of the one hundred most popular passcodes. Mathematically, the problem of using just one popular passcode is fundamentally the same as that of using a short passcode!)

Sometimes, it's smart programming to write stupid programs, because the costs of designing, implementing, and maintaining more sophisticated software out-weigh the benefits. But, here, the WordPress programmers have opted for cheapness in a way that needlessly thwarts and insults some users, and can actually make systems less secure in those cases. (And the poor diagnostics are simply inexcusable.)

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