6 ms·

As I wrote in another comment, high entropy passwords by definition must be hard to remember. It's not strictly true, but it definitely refutes the title of thi

by tel 16y ago

As I wrote in another comment, high entropy passwords by definition must be hard to remember. It's not strictly true, but it definitely refutes the title of this submission. While I think this post is rather optimistic in its calculations — using maximum entropy distributions, for instance — it does bring up a good point: Personally memorable nonsense sentences are rather high entropy. Actual practical guessing is not pure distribution entropy but instead closer to the KL divergence since an intelligent brute force guesser has to make assumptions about the password distribution in order to reap benefits. If your password comes from an expected distribution (letters in English words, words in English sentences) you're losing a whole lot of potential entropy, traded for particular memorability. If you can hedge between those bets, though, you're in a good place. "this is fun" is not actually terribly secure compared to "J4fS!2" unless you're actually attacked by a uniform dictionary brute force search. "slurping radicals debilitate enzymatically" is super high entropy and quite likely easier to remember than "J4fS!2".

tlrobinson 16y ago
In practice is a long nonsense sentence of English words really any better than an equally long coherent sentence of English words? Are cracking tools really that intelligent?
- tel 16y ago
  Maybe not yet, but lots of people are attacking NLP and thus building all the components of cracking tools that are that smart.
- jtheory 16y ago
  It's not at all about how intelligent the cracking tools are; it's about how unimaginative users tend to be. Let's say the suggestion "use an easy to remember sentence, rather than a short password" gets around. The actual set of easy-to-remember sentences for a large set of users will include some very good ones, but mostly a small set of simple ones, like "To be or not to be", "Seize the day" and so on. The cracking programs don't need to figure out what those are -- they just need ONE password dump from a site with poor security (easy to find, unfortunately), and the analysis is trivial. The other downside of sentences, though, is that even when the average person picks an easy-to-remember sentence, it's still hard to remember exactly how they wrote it last time (upper-case, all lower, what punctuation?), and for poor typists, think about the chances of making a typo (or just forgetting where they were) while typing out all those little stars....
cookiecaper 16y ago
I think this is the real key. Sentences as passwords are really hard to crack as long as you choose a reasonably long sentence that you can remember easily but is not overly simplistic or obvious, and if you include a few typos or non-standard capitalization and/or punctuation it becomes that much more difficult to crack. A sentence is the only way you'll get normal users to memorize a password > 6 chars. I think a sentence is much better than what most people end using, which is a personally significant word (like a child, spouse, or pet's name) + a brief personally significant numeric suffix (like birth year).
- sukuriant 16y ago
  to memorize a "good" password > 6 characters
tzs 16y ago
I once did the following for a password that I wanted to be able to remember, but that I wanted to be very secure against attack. It was easy to remember, yet very effective. How does this fit into the entropy vs. rememberability thing? 1. Take a 100x100 binary matrix, initialized to 0. 2. Change some bits to 1, in a pattern that I memorized. It was just something simple, like my initials in dot-matrix form. 3. Apply Conway's Life cellular automata rules to the matrix, with no wrap, doing 108 iterations. 4. Read out the final state of each cell row by row, as a an ASCII representation of a binary string of 10000 bits. 5. Run that through MD5. Iterate this 1960 times. 6. The final MD5, as an ASCII representation of a 128-bit hex number, was my password. I did NOT have any of the software for this on any computer. Whenever I needed this password, I'd write a Life program, enter my memorized pattern, run it, do the MD5 stuff, and then delete the program. Effectively, my password was the combination of the Life algorithm, the size of the input, the input pattern, the number of iterations to run of Life, and the algorithm for converting the final Life state into an ASCII password string. There seems to be a lot of entropy here. Yet it was pretty easy to remember.
- jerfelix 16y ago
  Let me guess, you're a 50-year old Libra.
  - tzs 16y ago
    I assume you guessed 50 from the fact that I iterated MD5 1960 times so assume that was my birth year. That is correct. I don't see how you (incorrectly) guessed Libra. If you took the 108 as the 108th day of the year and assumed that was my birthday, that would be April 18th, which would be Aries. If you took it as meaning January 8th, that would be Capricorn. Did you assume it was 10/8? That would give Libra. Anyway, the 108 is not a date. It refers to Math 108, an undergraduate math course at Caltech that bestows a curse upon those who take it. Forever afterward, the number 108 starts appearing in their lives more than normal. One girl I knew there went so far as to build a digital clock that held 1:07 for two minutes so that she would stop seeing 1:08 on her clock.
    - 16y ago
qjz 16y ago
Yet, if your Gawker password had been "passwords delight entropy enthusiasts", it would have been cracked immediately, due to the 8-character truncation. "i<3turtles" would probably have been much safer. Unfortunately, users rarely know anything about the systems used for authentication, so any advice should keep poor systems in mind. That's why I frontload my passwords with a few characters of high entropy before appending a longer high entropy (but memorable) phrase.
- tel 16y ago
  Good point. I fully admit that I assumed that my password wasn't truncated. I should probably frontload as well.
  - deleted 16y ago
    [deleted]

by tel 16y ago

tlrobinson 16y ago

In practice is a long nonsense sentence of English words really any better than an equally long coherent sentence of English words? Are cracking tools really that intelligent?

tel 16y ago
Maybe not yet, but lots of people are attacking NLP and thus building all the components of cracking tools that are that smart.
jtheory 16y ago
It's not at all about how intelligent the cracking tools are; it's about how unimaginative users tend to be. Let's say the suggestion "use an easy to remember sentence, rather than a short password" gets around. The actual set of easy-to-remember sentences for a large set of users will include some very good ones, but mostly a small set of simple ones, like "To be or not to be", "Seize the day" and so on. The cracking programs don't need to figure out what those are -- they just need ONE password dump from a site with poor security (easy to find, unfortunately), and the analysis is trivial. The other downside of sentences, though, is that even when the average person picks an easy-to-remember sentence, it's still hard to remember exactly how they wrote it last time (upper-case, all lower, what punctuation?), and for poor typists, think about the chances of making a typo (or just forgetting where they were) while typing out all those little stars....

cookiecaper 16y ago

I think this is the real key. Sentences as passwords are really hard to crack as long as you choose a reasonably long sentence that you can remember easily but is not overly simplistic or obvious, and if you include a few typos or non-standard capitalization and/or punctuation it becomes that much more difficult to crack. A sentence is the only way you'll get normal users to memorize a password > 6 chars. I think a sentence is much better than what most people end using, which is a personally significant word (like a child, spouse, or pet's name) + a brief personally significant numeric suffix (like birth year).

sukuriant 16y ago
to memorize a "good" password > 6 characters

tzs 16y ago

I once did the following for a password that I wanted to be able to remember, but that I wanted to be very secure against attack. It was easy to remember, yet very effective. How does this fit into the entropy vs. rememberability thing? 1. Take a 100x100 binary matrix, initialized to 0. 2. Change some bits to 1, in a pattern that I memorized. It was just something simple, like my initials in dot-matrix form. 3. Apply Conway's Life cellular automata rules to the matrix, with no wrap, doing 108 iterations. 4. Read out the final state of each cell row by row, as a an ASCII representation of a binary string of 10000 bits. 5. Run that through MD5. Iterate this 1960 times. 6. The final MD5, as an ASCII representation of a 128-bit hex number, was my password. I did NOT have any of the software for this on any computer. Whenever I needed this password, I'd write a Life program, enter my memorized pattern, run it, do the MD5 stuff, and then delete the program. Effectively, my password was the combination of the Life algorithm, the size of the input, the input pattern, the number of iterations to run of Life, and the algorithm for converting the final Life state into an ASCII password string. There seems to be a lot of entropy here. Yet it was pretty easy to remember.

jerfelix 16y ago
Let me guess, you're a 50-year old Libra.
- tzs 16y ago
  I assume you guessed 50 from the fact that I iterated MD5 1960 times so assume that was my birth year. That is correct. I don't see how you (incorrectly) guessed Libra. If you took the 108 as the 108th day of the year and assumed that was my birthday, that would be April 18th, which would be Aries. If you took it as meaning January 8th, that would be Capricorn. Did you assume it was 10/8? That would give Libra. Anyway, the 108 is not a date. It refers to Math 108, an undergraduate math course at Caltech that bestows a curse upon those who take it. Forever afterward, the number 108 starts appearing in their lives more than normal. One girl I knew there went so far as to build a digital clock that held 1:07 for two minutes so that she would stop seeing 1:08 on her clock.
  - 16y ago

qjz 16y ago

Yet, if your Gawker password had been "passwords delight entropy enthusiasts", it would have been cracked immediately, due to the 8-character truncation. "i<3turtles" would probably have been much safer. Unfortunately, users rarely know anything about the systems used for authentication, so any advice should keep poor systems in mind. That's why I frontload my passwords with a few characters of high entropy before appending a longer high entropy (but memorable) phrase.

tel 16y ago
Good point. I fully admit that I assumed that my password wasn't truncated. I should probably frontload as well.
- deleted 16y ago
  [deleted]