C++/C Beginners Codebreak challenge

I thought it an idea to put a puzzle up for the less advanced programmers like myself to have a go at, this is a mixture of codebreaking and program creation, the point being building a program as a tool to break the code, without it this would take a long time to solve, unless you were born in bletchley park or something.

part1 > the program should be able to aid you break the cipher attached and output as plaintext, by accepting a test key. it should include a function to help your analysis of the testkeys, eg funtion to help determine key length by looking for repeated groupings.
part2 > Your program should also be able to encrypt the attached plaintext file using the same ciphertype and key and output it to a .txt file, this file will then be run in my test program.

I dont think it will take too long for someone to complete it so public answers posted here as attachments,

include the cipherkey as a comment at the top of your source file.
if you have the key correct but your program does not accurately output the plaintext thats a fail.

in the same format of my ciphertext (ie no whitespace, all lowercase letters, no punctuation)

console app only.

i use codeblocks but also have dev cpp so those are my options to compile your work, so ensure compatible.

The winning program will be a single source file, maximum of 200 lines, including empty lines.

only the usual headers for i/o allowed

This is a Vigenère cipher.

To the winner goes the glory, adulation of your peers, + people will no longer cross the street to avoid you! Also it might be a step on the road to solve the Beale papers... ;)

p.s i suppose its possible someone already has something to do this....so maybe let others have a go if so ;)!

you mean Vigenère cipher. meow.

I'm doing this by hand but I don't completely understand the instructions.

Quote:

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The Vigenère cipher function is essentially modulo arithmetic, and thus commutative. So if the key length is known (or guessed) then subtracting the cipher text from itself, offset by the key length will produce the cipher text encrypted with itself. If any words in the cipher text are known or can be guessed at then the plain text and hence the key will be revealed. This is useful if the key is an obscure sequence of letters because the plain text will generally be ordinary words.

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By the way I hate you for picking now to do this, but if I can crack it by hand, I will be able to write it algorithmically.... though there is not much a point at that point.

That is confusin description yes but wil make sense hindsight,several methods t attack this ciphertype,seek altern, 1st analysis is try determine keylength, laborious to crack by hand hence write program, merry christmas;-)!

When my wife and I first met we needed a secure method of exchanging "letters" and I came up with an algorithm to do so. The trick is that each message contained the key for the next one. Years later we can upon these messages and wanted to see what was in them but as with all things, memory degrades over time. I told you all of that simply to say that writing a code-breaker for those messages was a VERY interesting project......so this could be a great deal of fun. One approach involved using a dictionary to decode the first 100 bytes of the message, then "spell check" the resulting text. If the spell checker claimed more than a 50% success rate, the rest of the message was decoded using that word. This broke about 80% of the messages....not perfect but it had promise.

Yea, its a great exercise 4algorithms and similar t your point vignere cipher once considerd unbreakable,thing is using 1 time pad, bit like ur exampl can b made truly unbreakble cos even wit quantum power would only ever reveal all wrong messages also

Quote:

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Yea, its a great exercise 4algorithms and similar t your point vignere cipher once considerd unbreakable,thing is using 1 time pad, bit like ur exampl can b made truly unbreakble cos even wit quantum power would only ever reveal all wrong messages also

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Erm....what?

Quote:

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When my wife and I first met we needed a secure method of exchanging "letters" and I came up with an algorithm to do so. The trick is that each message contained the key for the next one. Years later we can upon these messages and wanted to see what was in them but as with all things, memory degrades over time. I told you all of that simply to say that writing a code-breaker for those messages was a VERY interesting project......so this could be a great deal of fun. One approach involved using a dictionary to decode the first 100 bytes of the message, then "spell check" the resulting text. If the spell checker claimed more than a 50% success rate, the rest of the message was decoded using that word. This broke about 80% of the messages....not perfect but it had promise.

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So I guess there was no way after that for you to hide your nerdiness and be 'cool' in her eyes? :D She definitely knew that she was marrying a nerd. But that's cool b/c nerd husbands are in high demand now. Ladies just about die when their e-mail and facebook don't work and so it's nerd husbands to the rescue. I'm thinking about getting a cape but that's probably going overboard.


Anyways, sounds like a fun challenge. I might give it a go.

Quote:

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Originally Posted by rogster001

Yea, its a great exercise 4algorithms and similar t your point vignere cipher once considerd unbreakable,thing is using 1 time pad, bit like ur exampl can b made truly unbreakble cos even wit quantum power would only ever reveal all wrong messages also

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I'm not wasting my time trying to crack a one-time pad if that's what your challenge is. :mad:

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adulation of your peers

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That's an odd incentive... perhaps the admiration of my peers...?

Whiteflags no way is it one time pad man, that would be nuts, to cactus hugger.. Use of word 'adulation' used in sense of 'tongue in cheek' to all, will tidy my post up for clarity, been away from pc and unable to reply properly

why cant i edit my original post? the button is only available on my last comment? anyway this line in the instructions >

Quote:

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in the same format of my ciphertext (ie no whitespace, all lowercase letters, no
punctuation)

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it should be 'your encrypted file should output in the same format as my ciphertext (ie no whitespace, all lowercase letters, no
punctuation)'

also because people may use different approaches to crack the cipher i think the requirements for the actual program pass need clarifying.

It is fundamental to try and determine the length of key, so your program must include a function that scans the coded document comparing sample length strings in the cipher for repeats,
Output the number of ocurrences for matching strings.
You can also complete this step by assuming a words like 'the' or 'then' exisit in the plaintext and by reversing how you use the alphabet grid by using 'the' to decrypt examine this output for repeat patterns that may provide clues to key.

note candidates for further analysis are normally only those with more than 2 hits, depending on the sample length you try, 2 or less may just be coincidence.

There would usually be a couple more analysis stages, the first would probably be a frequency test, but like i say there are different ways so it is hard to set the requirements without effectively outlining a step by step method myself and thus making the puzzle easier for those that just want to crack code.
So i will allow two additional functions that will not contribute to the total line count to help you with the final analysis, or complete this part by hand.
Any other suggestions welcome, if anyone thinks just change the requirements so that three functions for analysis are included or whatever.

do you know what the key is on that cipherdoc.txt ?

Quote:

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Originally Posted by kryptkat

do you know what the key is on that cipherdoc.txt ?

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Eh? Of course yes, its my encryption, thats the game

your encryption ? you mean your key using Vigenère ?

this is from a small function to extract that key. how did it do ?

Quote:

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your encryption ? you mean your key using Vigenère ?

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?? i mean i created the encrypted file using Vignére cipher and a key of my choosing, i hope thats a good enough reply ;)

i will have a look at the file now cheers :)

>>

Sorry Kryptkat, but i am not sure what you are showing here, if this is your submission for the 'encrypt the plaintext' part of the puzzle then it does not work with my key, it just produces what looks like another coded document.
also your character count is wrong so you must be going wrong somewhere there, if you eliminated all whitespace and punctuation it should be 1210, your document is 1184.

what key length are you testing?

The grid you have in the text file does not include the indexes, maybe you are taking this into account in your actual code but just not the printout, i am just suggesting maybe this was an oversight? or maybe you are just working the grid some other way without the need for the index

so the key is plain text ? not obscure sequence of letters ?
function took plaintextforencryption.txt removed all tokens and white spaces. ended up with 1184.
where chiperdoc.txt is 1210 to compare. why the diff in txt size ? meow messed something up ?
function printed the table with out index used diff method.
function used known plain txt size to extract key. it should have produced key. need to take another look and try to figure out what and why it did not work. using this to learn cpp better. prog is in cpp.
was testing the function.

Quote:

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why the diff in txt size ? meow messed something up ?

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haha maybe im looking at an older version than the one posted, i will check it, i only used word to count the characters, nothing else.

but hey i think you need to think about something there, the cipherdoc has nothing to do with the plaintext, they are seperate tasks and/so the character count is totally different.
god i am confusing myself now! All you need to do is work out the key to crack the cipherdoc, then this key will be used to encrypt the plaintext as a secondary task, which just becomes an exercise in string handling and arrays for example

bear in mind that just because you think the key may be N length, does not mean that it will divide into the coded text exactly,

Yes the key is just a normal english word, i was not going to make it so tough as to have a random key. or even one in a foreign language, though i completed a test like this from a cold start and the plaintext turned out to be a piece of french literature once decoded, which you could say made things 'slightly trickier' when analysing.

i have reattached an updated cipherdoc, it has a slight amendment as i saw a typo in the source document i used after checking through today, i have tested, including online crackers and the typo did not affect ability to crack with same techniques and key, but here is the amended version just to set it straight

tested another function. your key is 5 or 7 char. one word that came up is 'wires' is that in the ciphertext.doc or just one of those word that have no relation to the message text but just happen to show up ? i know it is not 'wires' because i tried it as the key. and many other words.

good work.. it sounds like you are getting somewhere, you are right wires is not the key, and i checked the source document, wires is not in there either, but i thought it might have been ;) just as a thought does your function as it stands let you correctly encrypt and decrypt test documents with a key of your own choosing? just in case...

ran in to a few errors. "can not convert a char constant" and " can not convert char * to char[] " and "can not convert char * to char * " and " link errors" .

more to be done. i do not think it is working correctly yet.

There's an error in the cipherdoc.txt from post 17 :) At character position 375 there should be a 'd' inserted.
I'm attaching a fixed version.

I'm currently working on getting my code to automatically find the key. It still needs a bit of manual poking to get the correct key. I'm also a bit over the <200 line requirement :(
Will post an update when/if I get it working correctly.

i did fix 'an' error in the text, i needed to replace two characters i think, did repost the correct version, why did you amend it again? it translates perfectly using my key? and also not just using my software but other third party cracker software online as a test using the key.

your posted 'corrected' version does not translate correctly using the key, you have letters missing, and not the ones i originally had to update so what are you on about?



200 lines was a bit tight i admit, just a guide i say.....;->

Hmm that's weird. Then either the forums or my browser must be doing something to corrupt the ciphertext. Can you please upload it again in a zip archive or similar that uses crc-verification?

it would have to be a .doc or .txt. this board does not let you put up .zip files.

what 200 line requirement ? meow ?

mind never i found it.

Quote:

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The winning program will be a single source file, maximum of 200 lines, including empty lines.

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apologies! there was a stray uppercase letter in my source doc, you were right _mike...i have now compared everything and we are singing from the same hymn sheet so, cipherdoc_fixed is the one to use, ay caramba....

And so congrats...you must have broken it??...you wanna PM me the keyword?

I've sent you a PM.
I will post a public solution on decrypting and encrypting the files here once I have some free time over to convert the C# winforms project I made to a console C++ app.

46 C:\Dev-Cpp\project333 misc\cvckeyfreq.cpp ISO C++ forbids comparison between pointer and integer

Code:

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    b =  strlen(a);

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Quote:

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output is 1867
on the fixed .doc ?

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on the fixed .doc ? why is the char count different not 1210 ?

i am still running into errors.

Quote:

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Originally Posted by kryptkat

on the fixed .doc ? why is the char count different not 1210 ?

i am still running into errors.

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I think you might be misunderstanding what the task is about.
The supplied cipherdoc and plaintext documents have nothing to do with each other really.
You are to crack the cipherdoc to find out the key used, and then use that same key to encrypt the plaintext document.

Kat mate i did try and point that out to you once before man ;)

Quote:

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cipherdoc_fixed.txt
"jnlpgfajtaoifmvfefbjdefbwsyupcslwadbbtiififdgotwl vievqhgejmpdewvijnwbqdoexkmeeivieeivjcstvbbdmupnuw oqlwbkogabkohwkqocwqxfdlpgjdwiqgatmvuejucdhavguhsb epudlrfrxwtnngblvslwpfmsbjfmsbkdadbctktcvbnqskodgn eblucnbtawpuhaaybslpgbnstauiuinfnyqpfmalpjnwbgfnlp efnlctzwzqeiwsakotwvffdsachefmtblkgocoducoihcnbtgz codziftoemqgtzmeiajieuejquuiuaqgtglczsuwoqulmttufn qstmvcuedgnjtltgseeikosgndbbtiifshzquolgrfcgurvtav inaupkoekktjtakcmtgtgsafkgtrwywjrwldzhaaobczqpfswf efevmfuhwtgwedwhueuppplgoabvsqnbbdmcutzmvjmwipetzw whhtidcaymuxojsybsxwtnadtaseuwioikmfcyjmuqeubgesuq gotankdifavjtmbkpnkbjfbjqvjszoqwejvofnlawtpwvffdxc peifohprzqueixngsefkgfnyqpfaflcgtwzcoaywpjsavixaab koghmtjovmpeevbjfpjwlfclbjfrwzgnaavqolqntbgempusgn dbbtiifshzquolgrfdanhfrwvefefokoesvfuhgciihwlgwolm fnokbqghaavjmwipelsziffgzvvnwbqxajludofavsuubkpngn jjssvcmylqeblwvijnwihuejpgoenmttuukgfdwlkocgurmelq phafgqghaaufvwzcmdwakhnknqsilogprymudhwcvaakegeikp rsifbgssmkefsknwmlqkqoslzwdtwlcnaupkoetiufdgvvievm ujgfahprtidcaymueixngsefkgfnyqpfifmkhhlmgofanvzfgc tuhaaobczqpfpjqpuevucuhwucuiuinbslzqooeqeblsvfbclc csistvbbdmuxilpwopjmefdwvvfdskevrskabnvectukmfcylp gcrabkthsvfbmwzkdafoqwejvofnlaviomojcatjchekeqskoi udofbkouwldzhaaupnzmpsyhzgwokbdbbtiifaxbgshaaffalp koeaojuewvufvwvvzofmviesvcmylqeblwvijnwectnwdgssmk efsknwmlqkqnpdmvfdsvfsafwpmysngxpjwisaeayjtzmocajz ctsavimygjxjomagsrgzucatjchegkevpamfuhwtwdakqcoczi ksoxucuhwucuiuacucsudsivoggrgugjgzbgfnlegotqmkhhlb qfiypvfefbjjrlgpjnwpgqlsggeafqoqojbcotjwnfifbjfekb cclaajnefbqgtzmctsgkkbtawpgojbjfavdcocwugotgnudiwv efaflviekbcuikbkdadaqdiwbamalmtdadtgetzmtpystuualq uuiuintouqguyzmcmsgivueexvfdlwtffgzouhwaejefbkgiuw thafqubtawptoxbjfpwzkpdopkmeuinmifowqofoqwejvofnli pesgkkftqbqhinmoprwuqoeqipepjmuuiymvpsuqgotankdefl gbvgzvirgciiombjjsdqhfbsjdbgweqskwlkomsvajnlmnmeub wblxqgmdkbaqiuinpfzqueaqipemslgdofbtjbmbkpnkbjbtow wmdzixfakawsevpktfsugjrjmuqeubkwegnvievqhgejmpdesv fbnstauiuinfnyqpfs"
b = strlen(a);
b = 1867 char long not the 1210 as first text file. you added more than just a 'd' ?

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i understand the challange. undo file 'a' get key use key to do file 'b'.

Code:

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    cout << strlen("jnlpgfajtaoifmvfefbjdefbwsyupcslwadbbtiififdgotwlvievqhgejmpdewvijnwbqdoexkmeeivieeivjcstvbbdmupnuwoqlwbkogabkohwkqocwqxfdlpgjdwiqgatmvuejucdhavguhsbepudlrfrxwtnngblvslwpfmsbjfmsbkdadbctktcvbnqskodgneblucnbtawpuhaaybslpgbnstauiuinfnyqpfmalpjnwbgfnlpefnlctzwzqeiwsakotwvffdsachefmtblkgocoducoihcnbtgzcodziftoemqgtzmeiajieuejquuiuaqgtglczsuwoqulmttufnqstmvcuedgnjtltgseeikosgndbbtiifshzquolgrfcgurvtavinaupkoekktjtakcmtgtgsafkgtrwywjrwldzhaaobczqpfswfefevmfuhwtgwedwhueuppplgoabvsqnbbdmcutzmvjmwipetzwwhhtidcaymuxojsybsxwtnadtaseuwioikmfcyjmuqeubgesuqgotankdifavjtmbkpnkbjfbjqvjszoqwejvofnlawtpwvffdxcpeifohprzqueixngsefkgfnyqpfaflcgtwzcoaywpjsavixaabkoghmtjovmpeevbjfpjwlfclbjfrwzgnaavqolqntbgempusgndbbtiifshzquolgrfdanhfrwvefefokoesvfuhgciihwlgwolmfnokbqghaavjmwipelsziffgzvvnwbqxajludofavsuubkpngnjjssvcmylqeblwvijnwihuejpgoenmttuukgfdwlkocgurmelqphafgqghaaufvwzcmdwakhnknqsilogprymudhwcvaakegeikprsifbgssmkefsknwmlqkqoslzwdtwlcnaupkoetiufdgvvievmujgfahprtidcaymueixngsefkgfnyqpfifmkhhlmgofanvzfgctuhaaobczqpfpjqpuevucuhwucuiuinbslzqooeqeblsvfbclccsistvbbdmuxilpwopjmefdwvvfdskevrskabnvectukmfcylpgcrabkthsvfbmwzkdafoqwejvofnlaviomojcatjchekeqskoiudofbkouwldzhaaupnzmpsyhzgwokbdbbtiifaxbgshaaffalpkoeaojuewvufvwvvzofmviesvcmylqeblwvijnwectnwdgssmkefsknwmlqkqnpdmvfdsvfsafwpmysngxpjwisaeayjtzmocajzctsavimygjxjomagsrgzucatjchegkevpamfuhwtwdakqcocziksoxucuhwucuiuacucsudsivoggrgugjgzbgfnlegotqmkhhlbqfiypvfefbjjrlgpjnwpgqlsggeafqoqojbcotjwnfifbjfekbcclaajnefbqgtzmctsgkkbtawpgojbjfavdcocwugotgnudiwvefaflviekbcuikbkdadaqdiwbamalmtdadtgetzmtpystuualquuiuintouqguyzmcmsgivueexvfdlwtffgzouhwaejefbkgiuwthafqubtawptoxbjfpwzkpdopkmeuinmifowqofoqwejvofnlipesgkkftqbqhinmoprwuqoeqipepjmuuiymvpsuqgotankdeflgbvgzvirgciiombjjsdqhfbsjdbgweqskwlkomsvajnlmnmeubwblxqgmdkbaqiuinpfzqueaqipemslgdofbtjbmbkpnkbjbtowwmdzixfakawsevpktfsugjrjmuqeubkwegnvievqhgejmpdesvfbnstauiuinfnyqpfs") << endl ;

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just to double check
output is

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C:\Dev-Cpp\project333 misc>cvckeyfreq
1867 string length
1867 double check string length
a z0 ==> 97
b z1 ==> 89
c z2 ==> 65
d z3 ==> 62
e z4 ==> 100
f z5 ==> 114
g z6 ==> 96
h z7 ==> 45
i z8 ==> 87
j z9 ==> 71
k z10 ==> 73
l z11 ==> 65
m z12 ==> 76
n z13 ==> 70
o z14 ==> 84
p z15 ==> 69
q z16 ==> 71
r z17 ==> 22
s z18 ==> 80
t z19 ==> 80
u z20 ==> 100
v z21 ==> 77
w z22 ==> 90
x z23 ==> 19
y z24 ==> 24
z z25 ==> 41

C:\Dev-Cpp\project333 misc>

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going to have to rest for a while.

edit add
when you add up all the numbers on the output you get 1867 char

Quote:

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b = 1867 char long not the 1210 as first text file. you added more than just a 'd' ?

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I started with the text file from post #17 which is 1866 chars. I have not checked the ciphertext from post 1 because by the time I found this thread rogster001 had already posted the updated version.
And please edit your post to add some line breaks to the cipher text, it's messing up the forum layout :)

Kat, forget len issues, mike posted 1867 len doc as i had not parsed a capital letter, last doc posted is correct, there is still time to win, get bustin that key!

ok. it will not let me edit it. strlen changed in progies. keep getting four or five different words then nothing fits.

What wont let u do what? I think you may be in situation where you need to refactor your code because i think your approach flawed from the outset maybe... And this cipher could be broken quick with just half the char count anyway

I will keep this contest open until 8th March, one user that i am aware of has broken the cipher but has coded in C#, thus i will keep contest open for further seven days, if no improvements are made on the current best effort then i will announce that as winner by default.

spent all weekend trying to figure out why the function was not returning the correct results. for example i would send a 'j' and 'a' which should have returned an 'j' but it returned and 'r'. the function looked correct.

unlike caesar where you have only one rot with this you have several characters that have to fit before anything looks like legible text. even when you find something it may only be accidental and not part of the message or the key. i made a prog that would test keys. found some interesting results.

with the key of 'troll' it returns 'cezar' in the first line but no other text. also found
'snap to a' as the first line again with no other text and
'victory am i' as part of the frst line with no other text. the key must fit before all of the message is displayed. part of the message may be displayed IF and only IF by chance you get a character in the correct spot in the key. with repeats you still have to find what fits .meow or throw fits. but that is what keeps it interesting. . also why it was once considered unbreakable.

thats right, it was once considered unbreakable, and as i mentioned earlier if you encrypt the entire text with a random key of the same length ( as in the one time pad system) it has mathematically been proved unbreakable as even with enough computing power to run all the permutations you would also get all the 'wrong' messages also, you could never be sure which was the right one, no good for intelligence gathering.

well just a few days left so good luck... interesting that cezar was generated as the first word there using troll haha

one time pads can be cracked. you just have to go through all the possible combinations.
that is the easy part. looking through more than 35 giggs of data to find something legible
that is the hard part.

thank you.

Quote:

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Originally Posted by kryptkat

one time pads can be cracked. you just have to go through all the possible combinations.
that is the easy part. looking through more than 35 giggs of data to find something legible
that is the hard part.

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The problem is, does the intercepted order read "monday attack cboard" or is it "do not attack cboard"? With a one time pad, both are equally likely, but if you guess wrong, cboard might be destroyed. This is what is meant by a one time pad being unbreakable. You can find the plain text, but you cannot identify it as the plain text with any confidence because there are so many alternatives that are equally likely to be the original plain text, even after you have discarded those that are not.

Quote:

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you just have to go through all the possible combinations.
that is the easy part. looking through more than 35 giggs of data to find something legible
that is the hard part.

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The point is exactly that which has just been reiterated, brute force attack on the one time pad would yield lots of messages that made perfect sense, and thus would be potential candidates for the correct message, thus rendering brute force attack useless.

in any case it is pure fantasy to even consider brute force attack as a method of attack for a one time pad,apart from the reason already mentioned the permutations are gargantuan and even given enough computing resource the time taken to attack it like this renders it redundant.
one time pad is just that, the next message sent is a new random key.

contest entry
prog cvcvigenerecontestentry.cpp

compiles using dev cpp

dejamewie if a key is found for the vigenere the rest of the text should fall in to place and make sense. if the same is true for the one time pad maybe. there is most likely to be an order to do something rather than an order not to do something. aka attack or retreat in lieu of sit there and do nothing.
bruteforcie of only thirteen char was 35 gig file. bruteforcie of only 4 was still 2gig found many with prog that are not part of text message or key. found may parts of words that did not fit eighter. finding the correct characters is still a matter of luck and some intellagence for the message interpatation.

Thanks for entry, see board on monday. You r stil missing point about one time pad though methinks, it is unbreakable in terms of pure math, as a stand alone codebreak, fact the pad could be stolen by your spies is a moot point

Quote:

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Originally Posted by kryptkat

dejamewie if a key is found for the vigenere the rest of the text should fall in to place and make sense. if the same is true for the one time pad maybe. there is most likely to be an order to do something rather than an order not to do something. aka attack or retreat in lieu of sit there and do nothing.

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I am not sure what you mean by "a key is found", but if rogster001's interpretation is correct then it does not matter, since encryption will always be "broken" if the attacker knows the key - the idea is to keep the key secret.

I suspect that your idea is this: by performing cryptanalysis on part of the ciphertext (e.g., the first block of a block cipher), one might be able to obtain a possible key that results in plausible plaintext. When one applies the decryption algorithm using this key on the rest of the ciphertext, the rest of the plaintext should fall into place and make sense.

The flaw in this with respect to the one time pad is that if you perform cryptanalysis on part of the ciphertext, you only get the possible key material that corresponds to that part of the ciphertext. A one time pad is characterised by the fact that there is at least as much key material as there is plaintext, so that every unit (e.g., bit) of the plaintext is encrypted with a different unit of the key material. Therefore, you cannot apply the decryption algorithm using this key on the rest of the ciphertext, since you do not have the key that corresponds to the rest of the ciphertext.

Furthermore, the key material that you do get is all the possible keys of the length of that portion of ciphertext that corresponds to a message that makes sense. Effectively, you are playing a pure guessing game to guess all sensible messages of that length. This is a rather hopeless task since you simply cannot know which of your guesses is the correct guess, with any confidence at all.

For example, instead of the two messages that I suggested, maybe the message is actually "kill: kryptkat only!". Since you reasoned that the message was "monday attack cboard", you went to the frontline and sacrificed yourself, thus enabling the enemy to easily achieve their objective. Thank you :)

Here's my entry. I really have to stop pushing everything ahead of me until the very last minute, I didn't have time to implement all the functions I wanted to include.

compiles with
$ g++ -Wall crypt.cpp -o crypt
for the basic command line version, or
$ g++ -Wall crypt.cpp -o crypt -DUSE_NCURSES -lncurses
for the somewhat improved ncurses gui version. Which also includes the command line functionality of course.
(for windows users; I don't know if ncurses is available as a native windows library or if you have to use cygwin. I have only tested under cygwin and linux.)

Usage:
Decrypt a file, printing to stdout
$ ./crypt d key < inputfile.txt

Encrypt a file, storing the result in another file
$ ./crypt e key < inputfile.txt > outputfile.txt

Replace "key" with the key you want to use for encryption/decryption.

Key analysis (requires compiling with ncurses)
$ ./crypt i
Then press F1 to load an encrypted file, and F2 to determine key length.
The F3 option isn't implemented yet (not enough time) but was planned to assist in cracking the key by scanning for character frequencies, which is how I found the OP's key in the first place. (except in C#)
F10 exits the application.

Quote:

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Originally Posted by rogster001

part1 > the program should be able to aid you break the cipher attached and output as plaintext, by accepting a test key. it should include a function to help your analysis of the testkeys, eg funtion to help determine key length by looking for repeated groupings.

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check. See the i option.

Quote:

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part2 > Your program should also be able to encrypt the attached plaintext file using the same ciphertype and key and output it to a .txt file, this file will then be run in my test program.

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check. See attached "encrypted.txt"

Quote:

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include the cipherkey as a comment at the top of your source file.

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check. See the first line of crypt.cpp

Quote:

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The winning program will be a single source file, maximum of 200 lines, including empty lines.

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Uhm.. my source uses a lot more than 200 lines so I failed to fulfill this requirement.

For those who don't feel like reading the source just to get the key, it's "basic"

The code has hardly any comments at all, and is quite a mess. (I blame it on being tired, and being high on coffee. It's 5am here) But at least I got a chance to try out ncurses :D
If anyone has any questions about something then feel free to ask.

Many congratulations to _Mike! He wins the contest!

He has matched the requirements on many of the criteria and actually broke the code itself some weeks ago with the key ' basic ' which he sent by PM to me.

A sterling effort to crack the cipher and a nice bit of code written as response to the problem, also of note is rewriting the original from C#.

thanks to Kryptkat also for additional entry, maybe now you have the key it will all make sense...! :-)

Attached is the source article which was encrypted, i have copied this from the webpage below, for the challenge i reworded some of it to avoid including numbers and also removed whitespace and punctuation etc.

Babbage Difference Engine

thanks to all for interest and comments, i still gonna post that indepth lecture on encryption history and one time pads though!...erm maybe not haha!

cheers!

congratulations _mike. very nice program too.

that was one of the first few words i did try. with both table reading functions. both apparently are messed up and nonfunctional <saddly punned> it was still an interesting and enjoyable contest.

could i see the original program used to encrypt it please ? i would like to try to find where i messed up.

laserlight when i said "a key is found" i was referring to the entire array the total length of the string or message. ie starting at aaaaa ==> to the end of string and ending fffff ==> to the end of the entire string message. brute force text example using key total length of message as said above. again the high amount of data obtained even with 2giggs to look through just for five char key. so then when that "key" is found the entire text should make sense.

Quote:

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For example, instead of the two messages that I suggested, maybe the message is actually "kill: kryptkat only!". Since you reasoned that the message was "monday attack cboard", you went to the frontline and sacrificed yourself, thus enabling the enemy to easily achieve their objective. Thank you

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<gulp?>

oh wow, you had the key by chance and the code let you down....the fickle hand of fate! bad news..

Why did your method stop at fffff? Surely it should have gone right to zzzzz? The key could have been zebra…

the brute force could certainly have worked to reveal the key as i had already let you know it was a normal English word of 5 character length, generating each and every combination of five letters then testing each one against the whole or part of the ciphertext as a key would have “eventually..” got you the right key... cycling through everything right up to zzzzz would have been more combinations than you could shake the proverbial stick at of course... knwing it was english word of 5 letters made this a viable option given enough time, no way brute force an efficient or "good" option if no idea of the key length or nature though...



Here is the part of my program that did the encryption, it was rough n ready just to get the job done >

Code:

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    sourcetext.open("babbage.txt");  //source
    sourcegrid.open("vigniere.txt"); //vignere table
    cipherdoc.open("cipherdoc.txt"); //output file for the cipher

    for(count = 0; count < FILELEN; count++)
    {
        sourcetext >> sourcedoc[count]; //write an array with the contents of sourcetext
        printf("%c", sourcedoc[count]);
        if(eol == 50)
        {
            printf("\n");
            eol = 0;
        }
        else
            eol++;
    }
    printf("\n");
    eol = 0;

    for(dwn = 0; dwn < 27; dwn++) //fill an array with the vignere table
    {
        for(acr = 0; acr < 27; acr++)
        {
            sourcegrid >> alphagrid[dwn][acr];
        }
    }
    sourcetext.close();
    sourcegrid.close();
   
    //use vignere table to encrypt //
    for(sourcecount = 0; sourcecount < FILELEN; sourcecount++) 
    {
        switch(keycount)  //this references the keyword chars as
        {                //indexed positions in the vignere table array
            case 0:
            keyindex = 2;
            break;
            case 1:
            keyindex = 1;
            break;
            case 2:
            keyindex = 19;
            break;
            case 3:
            keyindex = 9;
            break;
            case 4:
            keyindex = 3;
            break;
        }
        //go through the alphabet
        for(sourceindex = 0; sourceindex < 27; sourceindex++)
        {
            //if the alphabet letter matches the current character in the source text     
            if(alphagrid[0][sourceindex] == sourcedoc[sourcecount])
            { 
                //use the table to find the appropriate encrypted letter                 
                ciphertext[sourcecount] = alphagrid[keyindex][sourceindex];
                cipherdoc << ciphertext[sourcecount];// write the cipherletter to the output file
                printf("%c",ciphertext[sourcecount]);
                sourceindex = 27;  //break loop as letter is encrypted
                eol++;
            }
            if(eol > 50)
            {
                printf("\n");
                eol = 0;
            }
        }
        if(keycount == 4)
        {
            keycount = 0;
        }
        else
            keycount++;
    }
    printf("\n\n");
    cipherdoc.close();
    eol = 0;
    keycount = 0;

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that should read "zzzzz". thank you for that part of it. i would like to see the un part. i see you hard wired the key in. 2 1 19 9 3 "basic" i am still looking at it.

Quote:

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Originally Posted by kryptkat

laserlight when i said "a key is found" i was referring to the entire array the total length of the string or message. ie starting at aaaaa ==> to the end of string and ending fffff ==> to the end of the entire string message. brute force text example using key total length of message as said above. again the high amount of data obtained even with 2giggs to look through just for five char key. so then when that "key" is found the entire text should make sense.

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Are you talking about a one time pad? If you are talking about a one time pad, and if you understand the principle behind a one time pad, then you should have been able to see that my explanation applies: there are many keys that you can find such that the entire text would make sense, and all of them are equally likely.

The use of a one time pad makes for theoretically unbreakable encryption, regardless of the amount of storage and processing capability the adversary has. You may be able to store infinitely many bytes and process everything instantly, but unless you know the key (or a sufficiently large portion thereof), you will still not be able to distinguish one plausible plaintext from another, without relying on external information (by which time the information gleaned from decryption may be useless).

Yes it was hardwired key as I said it was rough and ready, and as the question setter I could indulge myself with these things and I had no real need to test keys haha.
The decrypt loop is exactly the same structure really but you just swap around the order of matching the characters to produce plaintext instead of cipher, you could remove the hardcoded key in this section and accept input instead to test freely of course.

And yes the amount of data produced by a onetime pad is (although guaranteed to be huuuuge) not really relevant, point is if you somehow had generated all the permutations of a message so encrypted and you were able to review all the different outputs then of the ones that made sense you could never tell with certainty which was the correct one.

The one time pad differs from other encryption in this way, ie even if all perms are revealed then this on its own does not mean it is usefully broken.

Cryptography has developed over time in something akin to an arms race,

The cryptographers are trying to achieve the perfect balance between the security of the encryption method itself, the security of the decryption method (which includes human elements), and the reusability of the method which includes speed of use, ability to easily replicate, portability.

The codebreakers try to to attack these elements thus making the cipher unusable, obsolete.

The one time pad does not check some of the boxes mentioned so despite the absolute security of the encryption it has been used only in specialized less dynamic applications, secure communication between presidents for example.

Methods using giant primes like in pgp / rsa are the preferred choice for common encryption now they are ingenious systems that match every requirement, the flaw is they depend on, ( like many other ciphers historically) the fact that current technology and equipment cannot break them by brute force analysis, not unless you have several centuries and all of the worlds computing power combined that is.
Of course this can only mean that eventually it will be obsolete also, a quantum computer would render it so overnight.

Quote:

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Originally Posted by rogster001

The one time pad does not check some of the boxes mentioned so despite the absolute security of the encryption it has been used only in specialized less dynamic applications, secure communication between presidents for example.

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The main problem concerning the use of a one time pad is key management: the key material must be established in advance over a secure channel, be sufficient for all secure communication until new key material can be established, and then only ever used once.

Quote:

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The main problem concerning the use of a one time pad is key management: the key material must be established in advance over a secure channel, be sufficient for all secure communication until new key material can be established, and then only ever used once.

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yes, and any hint of a compromise in the process and the whole thing has to be trashed and started again... who would want to be an encryption expert eh haha

no matter how much processing power and storage anyone may have analysis of the data is very subjective that is why it is an art. as said already there are many factors that go in to the analysis.

Quote:

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use of a one time pad makes for theoretically unbreakable encryption

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whos theory ? <sarcasm> cuzz you know that is going to be an unbiased opinion </sarcasm> meow.
the person that first created the one time pad ?

it is irrelevant how the data is interpreted or how the message data is used. once it is exposed then it is broken.

<joke> <gives laser big red websters dictionary> here is a book of just about every word you could write in an encrypted message therefore everything you could have written or write in the future has been broken right here.... your messages are in this book all you have to do is find them. </joke>

Quote:

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here is a book of just about every word you could write in an encrypted message therefore everything you could have written or write in the future has been broken right here.... your messages are in this book all you have to do is find them.

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Haha i love the irony, that is the point exactly with all the variations that would come from one time pad...its just a jumble of all posssible messages haha.

And am not going to argue semantics with you too much but simply revealing every possible permutation of a message most definitely does not mean it is broken, it just means you have managed to generate every permutaion but are no closer to knowing the true one, thus it may as well still be encoded.... in effect it still is encoded as you.. 'cannot see the wood for the trees'

Quote:

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Originally Posted by kryptkat

no matter how much processing power and storage anyone may have analysis of the data is very subjective that is why it is an art. as said already there are many factors that go in to the analysis.

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I do not see what this has to do with whether the use of a one time pad makes for unbreakable encryption when used correctly. Yes, these other factors can allow one to deduce the plaintext, but it does not constitute breaking the encryption in the same way as say, a side channel attack to obtain the secret key when AES is used. For the latter, the secret key obtained can then be used to decrypt other ciphertext, but with a one time pad the process begins anew for new ciphertext, because the key is always different.

Quote:

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Originally Posted by kryptkat

whos theory ? <sarcasm> cuzz you know that is going to be an unbiased opinion </sarcasm> meow.
the person that first created the one time pad ?

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It is unbiased. I suggest that you actually read up on the mathematics before you sprout such nonsense.

Quote:

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Originally Posted by kryptkat

it is irrelevant how the data is interpreted or how the message data is used. once it is exposed then it is broken.

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What do you mean? Obviously, if you as an attacker somehow know the plaintext corresponding to the ciphertext, then the secrecy of that plaintext is broken, but that has no bearing on other ciphertext encrypted with a one time pad.