6 ms·

Even if you've provided information which narrows your password down to ~5,000 possible values, you've effectively handed out your password to one of 5,000 inte

Even if you've provided information which narrows your password down to ~5,000 possible values, you've effectively handed out your password to one of 5,000 internet strangers whom you will never meet in real life. Then consider that this is Hacker News, and how many of those 5,000 have both the skills and motivation to exploit the information you've provided. Never give out "hints" about your password. Not its contents, not its exact length, the physical location in which you store a copy, nothing.

Dylan16807 8y ago
If giving out the length hurts anything, there's enough going wrong that you should probably assume it's already compromised. Unless there's something fundamentally wrong with the password, a public length of n is almost as secure as a secret length of n, and significantly more secure than a secret length of n-1 Never get into the specifics of a password, but explaining the basic structure should be a tiny impact and well within your margin of safety, or you didn't make a good enough password to start with.
- kakarot 8y ago
  I'm willing to believe that if you could help me understand a bit more why that is so.
  - infogulch 8y ago
    Think of it this way: assume someone is trying to brute force your password. For simplicity let's say they know nothing about it, except that its characters are randomly drawn from a 50 character pool. As they guess passwords starting with 1 character, each added character takes 50x longer than all previous guesses put together to guess all possible passwords of that length. Put another way, if they knew the length beforehand, it would only save them from testing about 2% of the overall possible combinations.
    - kakarot 8y ago
      Gotcha. I guess I was unclear about what "almost as secure" meant in this context. So whether providing your length is a tangible security leak or not is essentially a function of the size of your character pool, because if your password is short enough for n-1 to contain a significant percentage of possible combinations then it's probably already short enough to brute force anyway.
      - Dylan16807 8y ago
        That's not right. You can make a secure password using only ABC as your character pool, if you make it 60 characters long. In that case the percentage of combinations covered by n-1 is a full third of the n character combinations, and your attacker can get a 25% speed boost by you revealing the length. But it's still more secure than a 59 character password, and far more secure than a 57 character password, and all of them are extremely secure. A good way to look at it is to measure the password in bits of randomness. At most, revealing length can shave off one bit. For any reasonable character set it shaves off a small fraction of a bit. And one bit does not make the difference between good or borderline or bad.
        kakarot 8y ago
        A 25% speed boost is what I would call a significant percentage. Especially at 60 characters. My statement holds up.
        Dylan16807 8y ago
        What you're missing is that a 59 character password (with secret length) is extremely secure, despite the even larger speed boost. If you worry about any speedup in password cracking that is less than an order of magnitude, your password was too close to failing to start with. Make your password 5% longer, which will make it at least 20x slower to crack, and then you won't have to care if "20x" gets reduced to "15x". You may say "It's not harmless to give up 25%. What if I give up 25% several times? That could make even a good password become insecure." but there's a limit to how much speedup someone can get from knowing the structure of your password. And the best way to evaluate the strength of a password is to assume that all the structure is public. So I can say that my typical passwords, being 20 mixed-case letters and numbers, all have a security of 2^119. It's possible that an attacker that uses the wrong algorithm would have to guess even more, but I'm not just worried about a clumsy attacker, I'm also worried about a moderately-high-quality attacker. It's a bad idea to depend on that extra .1 bit I could get with this character set, or that extra .4 bits I could get with a smaller character set. Just assume the length is known.
  - rustyfe 8y ago
    We'll take 60 possible characters (alphanumeric with caps and a few special characters). The summation 1...N of 60^x is (60/59) (60^N - 1). Known length is 60^N. If we assume N is big enough that the minus one isn't important, you can see going from known to unknown only increases the guesses by a factor of 60/59!
- dTal 8y ago
  While you're correct mathematically, I still think it's a good habit to give zero information about your password. If you attempt to estimate the information leakage with every "hint", sooner or later you'll slip up.
  - z29LiTp5qUC30n 8y ago
    My view is your secrets should be secure even if the attacker knows everything about how they are generated and used. For example: My password is 8192 characters long, leveraging only the ASCII character set (except \n\r\t\0) It is changed every 28days at 11:05am It is only used on exactly 1 website and the username on that website is also only used on that website and randomly generated as well. Good luck (Tell me how and where I can make this stronger)
    - FabHK 8y ago
      With your username, I actually believe you...
    - kakarot 8y ago
      Telling someone your password is 8 characters long and memorable vs telling them it is 8192 characters long and unrecallable are two entirely different things.
    - tripzilch 8y ago
      > Tell me how and where I can make this stronger Make it 8193 characters long, change it every 27 days at 11:04am, but most importantly: use it on exactly 0 websites. Good luck
    - asveikau 8y ago
      This is a very hilarious post. Bravo, sir, or brava, madam. (Revealing your gender would likely be a security risk - if you leave that unspecified it doubles the space of possibilities!) I don't know what joyless types would downvote you.
onychomys 8y ago
Sure, many of us have the skills to exploit that information, but the motivation? This isn't Mos Eisley.
- kakarot 8y ago
  Well I was referring to the intersection between the two. Out of all of the potential people to see OP's post here, there is a much higher likelihood of at least one of them containing both the skillset and the motivation required to exploit the information than on other popular aggregators.
- imtringued 8y ago
  I can already see it. 2 weeks later he will post about having made a fortune with BTC and losing it all.
bigbadgoose 8y ago
Plot twist, he's actually phishing this forum for the "I used that password too!" comment replies. _Taps side of head with index finger_

Dylan16807 8y ago

If giving out the length hurts anything, there's enough going wrong that you should probably assume it's already compromised. Unless there's something fundamentally wrong with the password, a public length of n is almost as secure as a secret length of n, and significantly more secure than a secret length of n-1 Never get into the specifics of a password, but explaining the basic structure should be a tiny impact and well within your margin of safety, or you didn't make a good enough password to start with.

kakarot 8y ago
I'm willing to believe that if you could help me understand a bit more why that is so.
- infogulch 8y ago
  Think of it this way: assume someone is trying to brute force your password. For simplicity let's say they know nothing about it, except that its characters are randomly drawn from a 50 character pool. As they guess passwords starting with 1 character, each added character takes 50x longer than all previous guesses put together to guess all possible passwords of that length. Put another way, if they knew the length beforehand, it would only save them from testing about 2% of the overall possible combinations.
  - kakarot 8y ago
    Gotcha. I guess I was unclear about what "almost as secure" meant in this context. So whether providing your length is a tangible security leak or not is essentially a function of the size of your character pool, because if your password is short enough for n-1 to contain a significant percentage of possible combinations then it's probably already short enough to brute force anyway.
    - Dylan16807 8y ago
      That's not right. You can make a secure password using only ABC as your character pool, if you make it 60 characters long. In that case the percentage of combinations covered by n-1 is a full third of the n character combinations, and your attacker can get a 25% speed boost by you revealing the length. But it's still more secure than a 59 character password, and far more secure than a 57 character password, and all of them are extremely secure. A good way to look at it is to measure the password in bits of randomness. At most, revealing length can shave off one bit. For any reasonable character set it shaves off a small fraction of a bit. And one bit does not make the difference between good or borderline or bad.
      - kakarot 8y ago
        A 25% speed boost is what I would call a significant percentage. Especially at 60 characters. My statement holds up.
        Dylan16807 8y ago
        What you're missing is that a 59 character password (with secret length) is extremely secure, despite the even larger speed boost. If you worry about any speedup in password cracking that is less than an order of magnitude, your password was too close to failing to start with. Make your password 5% longer, which will make it at least 20x slower to crack, and then you won't have to care if "20x" gets reduced to "15x". You may say "It's not harmless to give up 25%. What if I give up 25% several times? That could make even a good password become insecure." but there's a limit to how much speedup someone can get from knowing the structure of your password. And the best way to evaluate the strength of a password is to assume that all the structure is public. So I can say that my typical passwords, being 20 mixed-case letters and numbers, all have a security of 2^119. It's possible that an attacker that uses the wrong algorithm would have to guess even more, but I'm not just worried about a clumsy attacker, I'm also worried about a moderately-high-quality attacker. It's a bad idea to depend on that extra .1 bit I could get with this character set, or that extra .4 bits I could get with a smaller character set. Just assume the length is known.
- rustyfe 8y ago
  We'll take 60 possible characters (alphanumeric with caps and a few special characters). The summation 1...N of 60^x is (60/59) (60^N - 1). Known length is 60^N. If we assume N is big enough that the minus one isn't important, you can see going from known to unknown only increases the guesses by a factor of 60/59!
dTal 8y ago
While you're correct mathematically, I still think it's a good habit to give zero information about your password. If you attempt to estimate the information leakage with every "hint", sooner or later you'll slip up.
- z29LiTp5qUC30n 8y ago
  My view is your secrets should be secure even if the attacker knows everything about how they are generated and used. For example: My password is 8192 characters long, leveraging only the ASCII character set (except \n\r\t\0) It is changed every 28days at 11:05am It is only used on exactly 1 website and the username on that website is also only used on that website and randomly generated as well. Good luck (Tell me how and where I can make this stronger)
  - FabHK 8y ago
    With your username, I actually believe you...
  - kakarot 8y ago
    Telling someone your password is 8 characters long and memorable vs telling them it is 8192 characters long and unrecallable are two entirely different things.
  - tripzilch 8y ago
    > Tell me how and where I can make this stronger Make it 8193 characters long, change it every 27 days at 11:04am, but most importantly: use it on exactly 0 websites. Good luck
  - asveikau 8y ago
    This is a very hilarious post. Bravo, sir, or brava, madam. (Revealing your gender would likely be a security risk - if you leave that unspecified it doubles the space of possibilities!) I don't know what joyless types would downvote you.

onychomys 8y ago

Sure, many of us have the skills to exploit that information, but the motivation? This isn't Mos Eisley.

kakarot 8y ago
Well I was referring to the intersection between the two. Out of all of the potential people to see OP's post here, there is a much higher likelihood of at least one of them containing both the skillset and the motivation required to exploit the information than on other popular aggregators.
imtringued 8y ago
I can already see it. 2 weeks later he will post about having made a fortune with BTC and losing it all.

bigbadgoose 8y ago

Plot twist, he's actually phishing this forum for the "I used that password too!" comment replies. _Taps side of head with index finger_