I have some text generated by some lousy OCR software.
The output contains mixture of words and space-separated characters, which should have been grouped into words. For example,
Expr e s s i o n Syntax
S u m m a r y o f T e r minology
should have been
Expression Syntax
Summary of Terminology
What algorithms can group characters into words?
If I program in Python, C#, Java, C or C++, what libraries provide the implementation of the algorithms?
Thanks.
Minimal approach:
In your input, remove the space before any single letter words. Mark the final words created as part of this somehow (prefix them with a symbol not in the input, for example).
Get a dictionary of English words, sorted longest to shortest.
For each marked word in your input, find the longest match and break that off as a word. Repeat on the characters left over in the original "word" until there's nothing left over. (In the case where there's no match just leave it alone.)
More sophisticated, overkill approach:
The problem of splitting words without spaces is a real-world problem in languages commonly written without spaces, such as Chinese and Japanese. I'm familiar with Japanese so I'll mainly speak with reference to that.
Typical approaches use a dictionary and a sequence model. The model is trained to learn transition properties between labels - part of speech tagging, combined with the dictionary, is used to figure out the relative likelihood of different potential places to split words. Then the most likely sequence of splits for a whole sentence is solved for using (for example) the Viterbi algorithm.
Creating a system like this is almost certainly overkill if you're just cleaning OCR data, but if you're interested it may be worth looking into.
A sample case where the more sophisticated approach will work and the simple one won't:
input: Playforthefunofit
simple output: Play forth efunofit (forth is longer than for)
sophistiated output: Play for the fun of it (forth efunofit is a low-frequency - that is, unnatural - transition, while for the is not)
You can work around the issue with the simple approach to some extent by adding common short-word sequences to your dictionary as units. For example, add forthe as a dictionary word, and split it in a post processing step.
Hope that helps - good luck!
So I am taking a scripting test in Lua, and I am given this question:
Create an algorithm to generate a deck of cards, 1-52. Shuffle the deck of cards (do not use something like array.randomize() ). Then hand out 5 cards to two different players. Being that each card must be dealt to a different player at a time.
Typically I would do something like this to get a random number
local newDeck = {} --assume this array has all 52 cards in a playing deck
math.randomseed( os.time() )
local card = math.random(#newDeck)
...but it seems that the question is specifically asking that I do NOT use a stock math function.
(do not use something like array.randomize())
What would be the advantage to that? I can't imagine that the player of such a game would even notice a difference between random and pseudo random.
If only it were that simple. Most random number generators that are part of a language are linear congruential generators, meaning that the next term J, say, is related to the previous one I by
J = (aI + b) mod c
Where a, b, c are constants.
This means that it is possible to decipher the sequence from a single digit number of terms! (It's a set of simultaneous equations with bit of trickery to handle the modulus).
I'd say that an astute player is bound to notice the pseudo random nature of your sequence and may even game the system by unpicking your generator. You need to use a more sophisticated scheme. (Early attempts include Park-Miller and Bays-Durham; fairly well-known approaches).
I believe you are welcome to use the built in random number generator to get random numbers, but prohibited from using any built in array shufflers that may exist. How can you use a rng to have each card equally likely to be in each position?
you could just write something that draws a random card and puts it in the shuffled deck:
function shuf(tab)
local new = {}
for k=1,#tab do
new[#new+1]=table.remove(tab,math.random(#tab))
end
end
This approach makes sure you have no doubles.
I don't really think using a different RNG would matter that much unless you're doing cryptography, or something else that really matters.
Interpreting the question: just don't use a library function written for doing this. But there is a difference between a shuffler and a random number generator, since the latter can return double values while the former can't.
It's kind of interesting that pi's decimal representation never ends and never settles into a permanent repeating pattern. Meaning it's highly possible that pi contains every possible combination of numbers.
This guy calculated 5 trillions 5x(10^12) numbers of pi :D
http://www.numberworld.org/misc_runs/pi-5t/details.html
From the internet: "Converted into ASCII text, somewhere in that infinite string of digits is the name of every person you will ever love, the date, time and manner of your death, and the answers to all the great questions of the universe."
Wondering if somebody has already converted and analyzed the resulting string for known sequences of letters (words/sentences)?
Check out this page: http://pi.nersc.gov/.
It allows you to search for both character strings and hexadecimal sequences. Note that this search engine only has indexed the first 4 billion decimals of pi, and uses a formula for arbitrarily positioned binary or hexadecimal digits after those indexed.
The idea that Pi contains everything ever is a nice idea, but if it's correct, that means there is also an infinite amount of false things about everything ever. For example, if Pi contains a list of all the people you will ever love, then it will also have a list of people that seems that it is a list of people you will love, but in reality it's just a mix of names in a pattern that makes it look legit.
Following the same idea, the date, time, and manner of your death could also be "falsified". For example, let's say you are a man named Jason Delara, and you die at the age of 83 at 11:35 PM in your sleep. In Pi somewhere it can say in ASCII text "Jason Delara will die at age 83, 11:35 PM, passed in his sleep." It would also say somewhere else that "Jason Delara will die at age 35, at 6:00 AM, passed in a car accident." There could be an "infinite" amount of these false predictions.
There's also the fact that, if following the idea from above, all but one the answers to one of the great questions of the universe in that digit are wrong, even if many of the answers make sense. I've thought about this a lot, and I thought "What if there's part of the digit that states which facts are correct and which are not?" The answer is "Then there is an infinite amount of false lists in the digit claiming to do the same as the real list." In short, it would be pointless to convert Pi to ASCII text to try and figure everything out.
I know I'm a little late the party, but I wrote this for anybody who comes here looking for the answers to the universe in an endless, non-repeating decimal.
It is massively convenient that pi is an irrational number we're still finding digits for as if you can't find what you want in the sequence then by definition it just happens to be later on.
As for it containing hidden information - if you create any random sequence long enough, you'll be able to create simple words from the resulting output.
Conspiracy theorists just love to see patterns where there are none. They forget the other noise and are endlessly fascinated by mere coincidences.
Would just like to provide further context this question. Yes, the point is that PI goes on infinitely. That means there are endless possibilities for sentence structure and letter combination. This means every single combination of letters will happen and is happening in PI. So technically, everything in PI could apply to everything in the observable world around us.
Recently I wrote a Ruby program to determine solutions to a "Scramble Squares" tile puzzle:
I used TDD to implement most of it, leading to tests that looked like this:
it "has top, bottom, left, right" do
c = Cards.new
card = c.cards[0]
card.top.should == :CT
card.bottom.should == :WB
card.left.should == :MT
card.right.should == :BT
end
This worked well for the lower-level "helper" methods: identifying the "sides" of a tile, determining if a tile can be validly placed in the grid, etc.
But I ran into a problem when coding the actual algorithm to solve the puzzle. Since I didn't know valid possible solutions to the problem, I didn't know how to write a test first.
I ended up writing a pretty ugly, untested, algorithm to solve it:
def play_game
working_states = []
after_1 = step_1
i = 0
after_1.each do |state_1|
step_2(state_1).each do |state_2|
step_3(state_2).each do |state_3|
step_4(state_3).each do |state_4|
step_5(state_4).each do |state_5|
step_6(state_5).each do |state_6|
step_7(state_6).each do |state_7|
step_8(state_7).each do |state_8|
step_9(state_8).each do |state_9|
working_states << state_9[0]
end
end
end
end
end
end
end
end
end
So my question is: how do you use TDD to write a method when you don't already know the valid outputs?
If you're interested, the code's on GitHub:
Tests: https://github.com/mattdsteele/scramblesquares-solver/blob/master/golf-creator-spec.rb
Production code: https://github.com/mattdsteele/scramblesquares-solver/blob/master/game.rb
This isn't a direct answer, but this reminds me of the comparison between the Sudoku solvers written by Peter Norvig and Ron Jeffries. Ron Jeffries' approach used classic TDD, but he never really got a good solution. Norvig, on the other hand, was able to solve it very elegantly without TDD.
The fundamental question is: can an algorithm emerge using TDD?
From the puzzle website:
The object of the Scramble Squares®
puzzle game is to arrange the nine
colorfully illustrated square pieces
into a 12" x 12" square so that the
realistic graphics on the pieces'
edges match perfectly to form a
completed design in every direction.
So one of the first things I would look for is a test of whether two tiles, in a particular arrangement, match one another. This is with regard to your question of validity. Without that method working correctly, you can't evaluate whether the puzzle has been solved. That seems like a nice starting point, a nice bite-sized piece toward the full solution. It's not an algorithm yet, of course.
Once match() is working, where do we go from here? Well, an obvious solution is brute force: from the set of all possible arrangements of the tiles within the grid, reject those where any two adjacent tiles don't match. That's an algorithm, of sorts, and it's pretty certain to work (although in many puzzles the heat death of the universe occurs before a solution).
How about collecting the set of all pairs of tiles that match along a given edge (LTRB)? Could you get from there to a solution, quicker? Certainly you can test it (and test-drive it) easily enough.
The tests are unlikely to give you an algorithm, but they can help you to think about algorithms, and of course they can make validating your approach easier.
dunno if this "answers" the question either
analysis of the "puzzle"
9 tiles
each has 4 sides
each tile has half a pattern / picture
BRUTE FORCE APPROACH
to solve this problem
you need to generate 9! combinations ( 9 tiles X 8 tiles X 7 tiles... )
limited by the number of matching sides to the current tile(s) already in place
CONSIDERED APPROACH
Q How many sides are different?
IE how many matches are there?
therefore 9 X 4 = 36 sides / 2 ( since each side "must" match at least 1 other side )
otherwise its an uncompleteable puzzle
NOTE: at least 12 must match "correctly" for a 3 X 3 puzzle
label each matching side of a tile using a unique letter
then build a table holding each tile
you will need 4 entries into the table for each tile
4 sides ( corners ) hence 4 combinations
if you sort the table by side and INDEX into the table
side,tile_number
ABcd tile_1
BCda tile_1
CDab tile_1
DAbc tile_1
using the table should speed things up
since you should only need to match 1 or 2 sides at most
this limits the amount of NON PRODUCTIVE tile placing it has to do
depending on the design of the pattern / picture
there are 3 combinations ( orientations ) since each tile can be placed using 3 orientations
- the same ( multiple copies of the same tile )
- reflection
- rotation
God help us if they decide to make life very difficult
by putting similar patterns / pictures on the other side that also need to match
OR even making the tiles into cubes and matching 6 sides!!!
Using TDD,
you would write tests and then code to solve each small part of the problem,
as outlined above and write more tests and code to solve the whole problem
NO its not easy, you need to sit and write tests and code to practice
NOTE: this is a variation of the map colouring problem
http://en.wikipedia.org/wiki/Four_color_theorem
Background
While at the Gym the other day, I was working with my combination lock, and realized something that would be useful to me as a programmer. To wit, my combination is three seperate sets of numbers that either sound alike, or have some other relation that makes them easy to remember. For instance, 5-15-25, 7-17-2, 6-24-5. These examples seem easy to remember.
Question
How would I implement something similar for passwords? Yes, they ought to be hard to crack, but they also should be easy for the end user to remember. Combination Locks do that with a mix of numbers that have similar sounds, and with numbers that have similar properties (7-17-23: All Prime, 17 rolls right off the tongue after 7, and 23 is another prime, and is (out of that set), the 'hard' one to remember).
Criteria
The Password should be easy to remember. Dog!Wolf is easy to remember, but once an attacker knows that your website gives out that combination, it makes it infinitely easier to check.
The words or letters should mostly follow the same sounds (for the most part).
At least 8 letters
Not use !##$%^&*();'{}_+<>?,./ These punctuation marks, while appropriate for 'hard' passwords, do not have an 'easy to remember' sound.
Resources
This question is language-agnostic, but if there's a specific implementation for C#, I'd be glad to hear of it.
Update
A few users have said that 'this is bad password security'. Don't assume that this is for a website. This could just be for me to make an application for myself that generates passwords according to these rules. Here's an example.
The letters
A-C-C-L-I-M-O-P 'flow', and they happen to be two
regular words put together
(Acclimate and Mop). Further,
when a user says these letters, or
says them as a word, it's an actual
word for them. Easy to remember, but
hard to crack (dictionary attack,
obviously).
This question has a two-part goal:
Construct Passwords from letters that sound similar (using alliteration) or
Construct Passwords that mesh common words similarly to produce a third set of letters that is not in a dictionary.
You might want to look at:
The pronouncable password generation algorithm used by apg and explained in FIPS-181
Koremutake
First of all make sure the password is long. Consider using a "pass-phrase" instead of a single "pass-word". Breaking pass-phrases like "Dogs and wolves hate each other." is very hard yet they are quite easy to remember.
Some sites may also give you an advice which may be helpful, like Strong passwords: How to create and use them (linked from Password checker, which is a useful tool on its own).
Also, instead of trying to create easy to remember password, in some cases a much better alternative is to avoid remembering the password at all by using (and educating your users to use) a good password management utility (see What is your favourite password storage tool?) - when doing this, the only part left is to create a hard to crack password, which is easy (any long enough random sentence will do).
I am surprised no one has mentioned the Multics algorithm described at http://www.multicians.org/thvv/gpw.html , which is similar to the FIPS algorithm but based on trigraphs rather than digraphs. It produces output such as
ahmouryleg
thasylecta
tronicatic
terstabble
I have ported the code to python as well: http://pastebin.com/f6a10de7b
You could use Markov Chains to generate words that sounds like English(or any other language you want) but they are not actual words.
The question of easy to remember is really subjective, so I don't think you can write an algorithm like this that will be good for everyone.
And why use short passwords on web sites/computer applications instead of pass phrases? They are easy to remember but hard to crack.
After many years, I have decided to use the first letter of words in a passphrase. It's impossible to crack, versatile for length and restrictions like "you must have a digit", and hard to make errors.
This works by creating a phrase. A crazy fun vivid topic is useful!
"Stack Overflow aliens landed without using rockets or wheels".
Take the first letter, your password is "soalwurow"
You can type this quickly and accurately since you're not remembering letter by letter, you're just speaking a sentence inside your head.
I also like having words alternate from the left and right side of the keyboard, it gives you a fractionally faster typing speed and more pleasing rhythm. Notice in my example, your hands alternate left-right-left-right.
I have a few times used a following algorithm:
Put all lowercase vowels (from a-z) into an array Vowels
Put all lowercase consonants (from a-z) into another array Consonants
Create a third array Pairs of two letters in such a way, that you create all possible pairs of letters between Vowels and Consonants ("ab", "ba", "ac", etc...)
Randomly pick 3-5 elements from Pairs and concatenate them together as string Password
Randomly pick true or false
If true, remove the last letter from Password
If false, don't do anything
Substitute 2-4 randomly chosen characters in Password with its uppercase equivalent
Substitute 2-4 randomly chosen characters in Password with a randomly chosen integer 0-9
Voilá - now you should have a password of length between 5 and 10 characters, with upper and lower case alphanumeric characters. Having vowels and consonants take turns frequently make them semi-pronounceable and thus easier to remember.
FWIW I quite like jumbling word syllables for an easy but essentially random password. Take "Bongo" for example as a random word. Swap the syllables you get "Gobong". Swap the o's for zeros on top (or some other common substitution) and you've got an essentially random character sequence with some trail that helps you remember it.
Now how you pick out syllables programmatically - that's a whole other question!
When you generate a password for the user and send it by email, the first thing you should do when they first login if force them to change their password. Passwords created by the system do not need to be easy to remember because they should only be needed once.
Having easy to remember, hard to guess passwords is a useful concept for your users but is not one that the system should in some manner enforce. Suppose you send a password to your user's gmail account and the user doesn't change the password after logging in. If the password to the gmail account is compromised, then the password to your system is compromised.
So generating easy to remember passwords for your users is not helpful if they have to change the password immediately. And if they aren't changing it immediately, you have other problems.
I prefer giving users a "hard" password, requiring them to change it on the first use, and giving them guidance on how to construct a good, long pass phrase. I would also couple this with reasonable password complexity requirements (8+ characters, upper/lower case mix, and punctuation or digits). My rationale for this is that people are much more likely to remember something that they choose themselves and less likely to write it down somewhere if they can remember it.
A spin on the 'passphrase' idea is to take a phrase and write the first letters of each word in the phrase. E.g.
"A specter is haunting Europe - the specter of communism."
Becomes
asihe-tsoc
If the phrase happens to have punctation, such as !, ?, etc - might as well shove it in there. Same goes for numbers, or just substitute letters, or add relevant numbers to the end. E.g. Karl Marx (who said this quote) died in 1883, so why not 'asihe-tsoc83'?
I'm sure a creative brute-force attack could capitalise on the statistical properties of such a password, but it's still orders of magnitude more secure than a dictionary attack.
Another great approach is just to make up ridiculous words, e.g. 'Barangamop'. After using it a few times you will commit it to memory, but it's hard to brute-force. Append some numbers or punctuation for added security, e.g. '386Barangamop!'
Here's part 2 of your idea prototyped in a shell script. It takes 4, 5 and 6 letter words (roughly 50,000) from the Unix dictionary file on your computer, and concatenate those words on the first character.
#! /bin/bash
RANDOM=$$
WORDSFILE=./simple-words
DICTFILE=/usr/share/dict/words
grep -ve '[^a-z]' ${DICTFILE} | grep -Ee '^.{4,6}$' > ${WORDSFILE}
N_WORDS=$(wc -l < ${WORDSFILE})
for i in $(seq 1 20); do
password=""
while [ ! "${#password}" -ge 8 ] || grep -qe"^${password}$" ${DICTFILE}; do
while [ -z "${password}" ]; do
password="$(sed -ne "$(( (150 * $RANDOM) % $N_WORDS + 1))p" ${WORDSFILE})"
builtfrom="${password}"
done
word="$(sort -R ${WORDSFILE} | grep -m 1 -e "^..*${password:0:1}")"
builtfrom="${word} ${builtfrom}"
password="${word%${password:0:1}*}${password}"
done
echo "${password} (${builtfrom})"
done
Like most password generators, I cheat by outputting them in sets of twenties. This is often defended in terms of "security" (someone looking over your shoulder), but really its just a hack to let the user just pick the friendliest password.
I found the 4-to-6 letter words from the dictionary file still containing obscure words.
A better source for words would be a written document. I copied all the words on this page and pasted them into a text document, and then ran the following set of commands to get the actual english words.
perl -pe 's/[^a-z]+/\n/gi' ./624425.txt | tr A-Z a-z | sort -u > ./words
ispell -l ./words | grep -Fvf - ./words > ./simple-words
Then I used these 500 or so very simple words from this page to generate the following passwords with the shell script -- the script parenthetically shows the words that make up a password.
backgroundied (background died)
soundecrazy (sounding decided crazy)
aboupper (about upper)
commusers (community users)
reprogrammer (replacing programmer)
alliterafter (alliteration after)
actualetter (actual letter)
statisticrhythm (statistical crazy rhythm)
othereplacing (other replacing)
enjumbling (enjoying jumbling)
feedbacombination (feedback combination)
rinstead (right instead)
unbelievabut (unbelievably but)
createdogso (created dogs so)
apphours (applications phrase hours)
chainsoftwas (chains software was)
compupper (computer upper)
withomepage (without homepage)
welcomputer (welcome computer)
choosome (choose some)
Some of the results in there are winners.
The prototype shows it can probably be done, but the intelligence you require about alliteration or syllable information requires a better data source than just words. You'd need pronunciation information. Also, I've shown you probably want a database of good simple words to choose from, and not all words, to better satisfy your memorable-password requirement.
Generating a single password the first time and every time -- something you need for the Web -- will take both a better data source and more sophistication. Using a better programming language than Bash with text files and using a database could get this to work instantaneously. Using a database system you could use the SOUNDEX algorithm, or some such.
Neat idea. Good luck.
I'm completely with rjh. The advantage of just using the starting letters of a pass-phrase is that it looks random, which makes it damn hard to remember if you don't know the phrase behind it, in case Eve looks over your shoulder as you type the password.
OTOH, if she sees you type about 8 characters, among which 's' twice, and then 'o' and 'r' she may guess it correctly the first time.
Forcing the use of at least one digit doesn't really help; you simply know that it will be "pa55word" or "passw0rd".
Song lyrics are an inexhaustible source of pass-phrases.
"But I should have known this right from the start"
becomes "bishktrfts". 10 letters, even only lowercase gives you 10^15 combinations, which is a lot, especially since there's no shortcut for cracking it. (At 1 million combinations a second it takes 30 years to test all 10^15 combinations.)
As an extra (in case Eve knows you're a Police fan), you could swap e.g. the 2nd and 3rd letter, or take the second letter of the third word. Endless possibilities.
System generated passwords are a bad idea for anything other than internal service accounts or temporary resets (etc).
You should always use your own "passphrases" that are easy for you to remember but that are almost impossible to guess or brute force. For example the password for my old university account was.
Here to study again!
That is 20 characters using upper and lower case with punctuation. This is an unbelievably strong password and there is no piece of software that could generate a more secure one that is easier to remember for me.
Take look at the gpw tool. The package is also available in Debian/Ubuntu repositories.
One way to generate passwords that 'sound like' words would be to use a markov chain. An n-degree markov chain is basically a large set of n-tuples that appear in your input corpus, along with their frequency. For example, "aardvark", with a 2nd-degree markov chain, would generate the tuples (a, a, 1), (a, r, 2), (r, d, 1), (d, v, 1), (v, a, 1), (r, k, 1). Optionally, you can also include 'virtual' start-word and end-word tokens.
In order to create a useful markov chain for your purposes, you would feed in a large corpus of english language data - there are many available, including, for example, Project Gutenburg - to generate a set of records as outlined above. For generating natural language words or sentences that at least mostly follow rules of grammar or composition, a 3rd degree markov chain is usually sufficient.
Then, to generate a password, you pick a random 'starting' tuple from the set, weighted by its frequency, and output the first letter. Then, repeatedly select at random (again weighted by frequency) a 'next' tuple - that is, one that starts with the same letters that your current one ends with, and has only one letter different. Using the example above, suppose I start at (a, a, 1), and output 'a'. My only next choice is (a, r, 2), so I output another 'a'. Now, I can choose either (r, d, 1) or (r, k, 1), so I pick one at random based on their frequency of occurrence. Suppose I pick (r, k, 1) - I output 'r'. This process continues until you reach an end-of-word marker, or decide to stop independently (since most markov chains form a cyclic graph, you can potentially never finish generating if you don't apply an artificial length limitation).
At a word level (eg, each element of the tuple is a word), this technique is used by some 'conversation bots' to generate sensible-seeming nonsense sentences. It's also used by spammers to try and evade spam filters. At a letter level, as outlined above, it can be used to generate nonsense words, in this case for passwords.
One drawback: If your input corpus doesn't contain anything other than letters, nor will your output phrases, so they won't pass most 'secure' password requirements. You may want to apply some post-processing to substitute some characters for numbers or symbols.
edit: After answering, I realized that this is in no way phonetically memorable. Leaving the answer anyway b/c I find it interesting. /edit
Old thread, I know... but it's worth a shot.
1) I'd probably build the largest dictionary you can ammass. Arrange them into buckets by part of speech.
2)Then, build a grammar that can make several types of sentences. "Type" of sentence is determined by permutations of parts of speech.
3)Randomly (or as close to random as possible), pick a type of sentence. What is returned is a pattern with placeholders for parts of speech (n-v-n would be noun-verb-noun)
3)Pick words at random in each part of speech bucket to stand in for the placeholders. Fill them in. (The example above might become something like car-ate-bicycle.)
4)randomly scan each character deciding whether or not you want to replace it with either a similar-sounding character (or set of characters), or a look-alike. This is the hardest step of the problem.
5) resultant password would be something like kaR#tebyCICle
6) laugh at humorous results like the above that look like "karate bicycle"
I would really love to see someone implement passwords with control characters like "<Ctrl>+N" or even combo characters like "A+C" at the same time. Converting this to some binary equivalent would, IMHO, make password requirements much easier to remember, faster to type, and harder to crack (MANY more combinations to check).