Retype Your Password : Why should I ?

I have created countless accounts online, needless to say that i use only a small fraction of them in reality. In the process of creating these accounts i would have filled hundred if not thousands of forms which say Type your password in one row and Retype you password in the succeeding row. But I had never ever seriously analyzed  as to what I gain and what I loose by Retyping my password.

Recently I created an account and happily filled the Type your password and Retype your password fields in the form. I browsed the site that day. Few days later I tried to login to the website. "The username and passwords don't match" the server scowled at me. Bingo!! I tried few combinations, but all in vain. Rather than trying to recover my password, I set about to understand what had actually conspired against me.

And here goes my story : (Read this paragraph at the end)

What had actually happened was that I had mistyped my password. That's fair enough as all of us make mistakes. But what saddens me is that i had mistyped while retyping the password. Thats also acceptable though rare. But what interests me is that in both the cases my typos were same. So the poor system assumed that, what I typed was the actual password. And there I was blissfully ignorant of the my blunder. It would have been a tedious process to regain my password, if I had tried. But I didn't as I was busy analyzing what had happened and I was content with what I was doing.

Now lets analyse all the scenarios that arise in this context and see whether the extra effort we put in retyping the password is worth  it. There are four scenarios.

	Password[P] Correct	Password[P] Wrong
Retype Password[RP] Correct	Case I (P = RP)	Case II (P != RP)
Retype Password[RP] Wrong	Case III (P != RP)	Case IV  (P = RP)  OR (P !=RP)    V                   VI

Step 1 : Enter your Password

Step 2 : Retype your password

After completing Step 2, we can't differentiate between case I and V. After step 2 we also can't differentiate between Case II, Case III and case VI

Case I : Both Password and Retype password are correct - OK Scenario

Step 1 : The password is correct. So there is no need of Step 2, but since we don't know that password is correct we go to Step 2. That is where are trying to eliminate Case II here. But in the process we are creating chances for Case III, which is an unfavorable one.

Step 2 : Retype your password is also correct.  Hence we ended up in case, but we could as well have ended up in Case III.

Case II : Password is wrong and Retype password is correct - Ideal scenario

Step 1 : The password is incorrect. So in the absence of Step 2, your account would have been created with wrong password.

Step 2 : Retype your password is correct and hence you catch hold of the error in Step 1. But we could have as well ended up in Case IV

Case III : Password is correct but Retype password is wrong - A bad scenario

Step 1 : The password is correct. But at this step since we don't know that, we proceed to Step 2

Step 2 : The Retype password is wrong. Oooops though the password in Step 1 was correct we ended up in Case III and we will have to create our login again.

Case IV : Password is wrong but Retype password is wrong - A good/dangerous scenario

Step 1 : The password is wrong. Good that we have step 2

Step 2 : The Retype password is also wrong. Shit how could we mistype in second attempt also.

Now this is where this particular case gets interesting, if the typos in step1 and step 2 are different then we are saved and we have good scenario. It the typos in step 1 and step 2 happen to be the same then we are in for a toss. That's dangerous situation. Because we end up in what we tried to avoid. We will be erring with more confidence that we are right, which i think is more dangerous.

This is just the common sense analysis, the mathematical analysis with the use of probability shall follow ...