Comments on: Strong Passwords NEED Entropy

By: Aaron Toponce

Aaron Toponce — Wed, 29 Aug 2012 15:28:50 +0000

So, what are you disagreeing on? I’m not following. As mentioned in the article, length will give you more entropy for the cost, than fancy-pants uppercase, lowercase, numbers, symbols stuff. It’s not say that they aren’t important. They are. Very much. But, when it comes right down to it, attackers are looking for a needle in a haystack. They don’t know the length of your password, and they don’t now what sort of character sets you’re using. All they likely have, is a SHA1 hash of your password and maybe the salt. They likely don’t know anything else. Your password could be 1200 characters, it could be 12. It could be all lowercase, it could be some random leetspeak. Regardless, your needle is in a haystack. So the question remains: how large is the haystack they are looking through?

By: Justin

Justin — Wed, 29 Aug 2012 05:05:26 +0000

Thanks for the article. I know it’s old but I found it interesting. At the same time I have to disagree. You said it yourself:

“what gives you more entropy per bit- length or possible characters? If you passed college algebra, you would know that the answer is length, not total possible characters”

The only factor that really matters is the length of the password/phrase. This is because the cracker has no idea how much entropy is actually in the password, only the bit length. In order to crack it they have to assume maximum entropy and still try every possible combination within the bit length.

So, yes, entropy is important mathematically, but since the cracker is dealing with an unknown variable they have to assume the worst.

By: Aaron Toponce : Another Reminder About Passwords

Aaron Toponce : Another Reminder About Passwords — Fri, 08 Jun 2012 12:52:08 +0000

[...] you find the needle? Of course, the larger the haystack, the harder it will be to find the needle. I have also blogged about this in the past. Thankfully, Gibson Research Corporation has put together a web application that uses this analogy. [...]

By: Pequeño estudio de las contraseñas de las cuentas de Twitter «hackeadas», o por qué tu contraseña es una caca

Thu, 10 May 2012 19:07:10 +0000

[...] Si no sabes de qué estoy hablando pero te interesa el tema, intenta leer algo sobre entropía en las contraseñas. Algo como la entropía como una medida de la robustez de las contraseñas, o las passwords robustas NECESITAN entropía. [...]

By: Password Entropy

Password Entropy — Tue, 07 Jun 2011 21:47:10 +0000

[...] a password with 40 bits of entropy will create a hash with 40 bits of entropy if it is unsalted. This is the only source I could find where it was stated as fact. Is this correct? Thank [...]

[WORDPRESS HASHCASH] The comment’s server IP (74.86.156.59) doesn’t match the comment’s URL host IP (75.126.162.205) and so is spam.

By: What Really Makes a Password Strong? | Ian Dunn, Seattle web developer

What Really Makes a Password Strong? | Ian Dunn, Seattle web developer — Tue, 17 May 2011 23:21:47 +0000

[...] of the following rules to achieve the desired level of entropy, which at current standards is a minimum of 72 bits. That’s assuming that everything in the phrase is truly random, though. In reality there are [...]

By: Aaron

Aaron — Wed, 16 Mar 2011 14:49:32 +0000

@Random832- I am using entropy correctly. It’s a definition, and nothing more. Check out the Wikipedia article. It’s the maximum number of states that a system can be in. It is an upper bound. This is discussed in the post. And yes, passwords are just a subset of the ASCII set of characters, however, if you know a site restricts length or type of characters, then you have your starting point. Again, entropy is nothing more than a definition.

Also, the password card has an infinite searchable keyspace. I don’t understand why people don’t get this. Your password can be of infinite length and take any infinite amount of turns or directions. Sure, it has a subset of the the full ASCII set, so the possible number of characters is smaller, but as discussed in the post, it’s length that gets you entropy, not the total number of characters. Length is key, and length is in the card.

By: Random832

Random832 — Wed, 16 Mar 2011 13:19:09 +0000

If you’re going to fault them for not mentioning word “entropy” [while still hitting most of the other key points], you ought to use it correctly yourself. What you’re describing isn’t entropy, it’s a simpler keyspace-size concept [which is probably the upper bound of entropy]. In other words, you don’t really address why “password” has less entropy just because it only contains lowercase letters. I mean, lowercase letters are letters, they are alphanumeric, and they are ASCII. Isn’t that just “a good starting point in the search space”? On the other hand, it only _actually_ contains seven different characters, so why isn’t it 8*log_2(7)? And anyway, log_2(`wc -l /usr/share/dict/words`) is probably a better answer anyway.

Entropy is basically nothing _but_ an approximate measurement of how much [well, how little] a password is “a good starting point in the search space” – the “search space” here consisting of all possible strings from the empty string to a string 9999 characters long (or whatever your system limit is). And “password” probably doesn’t have 38 bits to begin with even ignoring it being a common first guess – english text only averages a little under three bits per letter, not the almost five implied by log_2(26). Which means that passphrases comprising intelligible sentences have to be a LOT longer than randomly generated passwords to have the same entropy.

And the keyspace size for your card gets to be a lot less if someone gets your card (I hope that’s not your real card) – your method is basically a dictionary-word password relying on a dictionary no-one else has.

By: Aaron

Aaron — Thu, 10 Mar 2011 13:15:57 +0000

I have various computers that I access. My personal laptop is running Debian Sid, which I’m using now. I have a Fedora 14 virtual machine, which I use at work that has Chrome 11.

By: Blimundus

Blimundus — Thu, 10 Mar 2011 10:53:00 +0000

“What happens if you lose your phone, only to find that you don’t have a backup?” > Dropbox syncs the passwords file with my computer, and I have daily/weekly/monthly incremental backups from my computer to an external harddisk.

“What happens when the developer of the software stops pushing updates?” > KeePassX is in the Debian repositories, and as long as it is in there, I can read my password file. If development on KeePassDroid stops, I may not be able to continue to use this password management system on my phone, and I will look for alternatives. If Dropbox stops, I can easily find another file syncing solution.

“What happens when you are at your friend’s computer, and your phone battery is dead?” > friend’s computer = power source. Now I just need to find a standard mini USB adapter and I can power my phone.

“So, congratulations on actually doing something about your security. Well done.” > Thanks! I’m glad I finally took action. Almost as good as when I finally started doing backups… (I admit I still have to test recovering data from the backup… it worked on day one though).

By the way, quite the jump from Chrome 9 to Chrome 11. I know, I am sending this from Internet Explorer 8.0… Our office pc’s all run Citrix, and the applications run in some off-site datacenter. We actuall switched from IE 6.0 to IE 8.0 only a couple of months ago. That was a great day: I could finally use tabs! :-s

By: Aaron

Aaron — Thu, 10 Mar 2011 00:19:46 +0000

Who said you have a finite number of lengths? I look at the card, I can find a password with 1,000,000 characters. Practical, no, but finite? Heh. You have an infinite number of characters in your password from the card, even if they repeat. You also have an infinite number of paths to take from an infinite combination of choices.

By: Duane Storey

Duane Storey — Wed, 09 Mar 2011 23:26:23 +0000

Isn’t the entropy of the password card significantly less than the entropy of the passwords on it? I mean, you have a finite number of starting positions and a finite number of lengths. Aren’t you essentially defeating the purpose of using a high entropy password by having the data on a card?

By: Aaron

Aaron — Wed, 09 Mar 2011 22:33:22 +0000

Yes, there is an encrypted version of the site, but I won’t link to it, mainly due to the fact that I don’t want to add additional stress to his server. If you are that concerned about the image going over the wire in “plain text”, then as you noticed, you can clearly go secure yourself. If the developer wasn’t concerned about HTTPS adding strain on his server, then I would gather that it would be default.

By: Heinjan

Heinjan — Wed, 09 Mar 2011 22:16:50 +0000

Time to rethink my password strategy!

I see the passwordcard site also has an encrypted site. Maybe a good idea to change the link to the https-version?

By: Aaron

Aaron — Wed, 09 Mar 2011 19:47:48 +0000

@Nicolai Hähnle: I’m not misleading anyone. Entropy is merely a measurement of size, not security. It’s a definition, and that’s it. I only mention the security of the sheer size of various entropies. However, what I’ve mentioned here isn’t the End All of entropy. Not by a long shot. Sure, you can measure the security of a password based on the seed used to build the random arrangement of characters, but that has nothing to do with entropy, other than after you have your string, it belongs to a certain entropy pool.

Calling my post dangerous is just draconian.