I've got what I think is a cipher (this isn't homework, just a challenge I thought I'd try to solve via coding for fun) which is:
"uiw uiw n la ltid mtel teacyihr n heeig sfsst"
To try to solve it, I'd like to iterate over every possible combination of cipher assignments for every letter in the alphabet (in an obviously brute force fashion), but I can't figure out an elegant way of going about that. Once I get the current iteration of the cipher assignment, I figure I'll transform the cipher text according to the cipher and then compare the first 3-letter word to a 3-letter wordlist and the last two words to a five letter wordlist, and if all three check out as being actual words, I'll have it print the results to file. This should give me a list of reasonable starting points to be able to weed out the incorrect results. If anyone has any ideas on how to go about implementing the iterative cipher I'd greatly appreciate it. Many thanks,
Peabody
You can have 26 for loop.
OK. I am kidding.
An obvious but inefficient version in pseudo code:
for i = 0 - 26^26-1
/* a = i/26^25 % 26
...
z = i/26^0 % 26 */
if all deciphered words are in the word list
print
end if
end for
By the way, I do not think it is the right way to decipher as said in your question, because I cannot find an example of double presence of a same word in an English sentence.
Related
Im new so if this question was already Asked (i didnt find it scrolling through the list of results though) please send me the link.
I got a math quiz and im to lazy to go through all the possibilities so i thought i can find a program instead. I know a bit about programming but not much.
Is it possible (and in what programming language, and how) to read only one digit, e.g at the 3rd Position, in a integer?
And how is an integer actually saved, in a kind of array?
Thanks!
You can get rid of any lower valued digit (the ones and tens if you only want the hundreds) by dividing with rounding/truncation. 1234/100 is 12 in most languages if you are doing integer division.
You can get rid of any higher valued digits by using taking the modulus. 12 % 10 is 2 in many languages; just find out how the modulus is done in yours. I use "modulus" meaning "divide and keep the rest only", i.e. it is the opposite of "divide with rounding"; that which is lost by rounding is the final result of the modulus.
The alternative is however to actually NOT see the input as a number and treat it as text. That way it is often easier to ignore the last 2 characters and all leading characters.
I'm trying to find 2 different plain text words that create very similar hashes.
I'm using the hashing method 'whirlpool', but I don't really need my question to be answered in the case or whirlpool, if you can using md5 or something easier that's ok.
The similarities i'm looking for is that they contain the same number of letters (doesnt matter how much they're jangled up)
i.e
plaintext 'test'
hash 1: abbb5 has 1 a , 3 b's , one 5
plaintext 'blahblah'
hash 2: b5bab must have the same, but doesnt matter what order.
I'm sure I can read up on how they're created and break it down and reverse it, but I am just wondering if what I'm talking about occurs.
I'm wondering because I haven't found a match of what I'm explaining (I created a PoC to run threw random words / letters till it recreated a similar match), but then again It would take forever doing it the way i was dong it. and was wondering if anyone with real knowledge of hashes / encryption would help me out.
So you can do it like this:
create an empty sorted map \
create a 64 bit counter (you don't need more than 2^63 inputs, in all probability, since you would be dead before they would be calculated - unless quantum crypto really takes off)
use the counter as input, probably easiest to encode it in 8 bytes;
use this as input for your hash function;
encode output of hash in hex (use ASCII bytes, for speed);
sort hex on number / alphabetically (same thing really)
check if sorted hex result is a key in the map
if it is, show hex result, the old counter from the map & the current counter (and stop)
if it isn't, put the sorted hex result in the map, with the counter as value
increase counter, goto 3
That's all folks. Results for SHA-1:
011122344667788899999aaaabbbcccddeeeefff for both 320324 and 429678
I don't know why you want to do this for hex, the hashes will be so large that they won't look too much alike. If your alphabet is smaller, your code will run (even) quicker. If you use whole output bytes (i.e. 00 to FF instead of 0 to F) instead of hex, it will take much more time - a quick (non-optimized) test on my machine shows it doesn't finish in minutes and then runs out of memory.
I'm trying to figure out how Twofish cipher expanded key is generated.
For now, I have figured out that firstly one part of the key is generated, and used for whitening, and then in each round 2x32bit key part is generated.
The first part of the key is made up of 3 vectors, Mo, Me and S.
Mo and Me are generated simply by expanding the primary key to first defined length, and splitting it to even and odd 32b words, that are then put in the Mo and Me vectors.
Vector S on the other hand is made up of k words, where k = N/64, in case of N=128, S contains 2x32b words.
So, we got to Mo(2x32) + Me(2x32) + S(2x32) + 16x2x32 = 38 32bit words. 2 words are missing. Why??
And what if N=192, or N=256? How can the expanded key be 40 32bit words instead of 41 and 44?
Any help would be great.
Thanks
To answer my own question, I found out that vectors Mo, Me and S are not actually part of the expanded key, as I first thought, actually they are just used for generating expanded key and key-dependent S boxes. Part of the key that is used for whitening is generated the same way as the parts that are used in each round, using h function, just they are not used anywhere else except for whitening. Hope this saves some trouble to people with this kind of question. :)
This is a Vigenere cipher-text
EORLL TQFDI HOEZF CHBQN IFGGQ MBVXM SIMGK NCCSV
WSXYD VTLQS BVBMJ YRTXO JCNXH THWOD FTDCC RMHEH
SNXVY FLSXT ICNXM GUMET HMTUR PENSU TZHMV LODGN
MINKA DTLOG HEVNI DXQUG AZGRM YDEXR TUYRM LYXNZ
ZGJ
The index of coincidence gave a shift of six (6): I know this is right (I used an online Java applet to decrypt the whole thing using the key 'QUARTZ').
However, in this question we are only told the first and last two letters of the Key - 'Q' and 'TZ.'
So far I have split the ciphertext into slices using this awesome applet. So the first slice is 0, k, 2k, 3k, 4k; the second is 1, k + 1, 2k + 1, 3k + 1; et cetera.
KeyPos=0: EQEQQSCXQJJHDEYIUTSVMTVUMTYJ
KeyPos=1: OFZNMICYSYCWCHFCMUULILNGYUX
KeyPos=2: RDFIBMSDBRNOCSLNERTONOIADYN
KeyPos=3: LICFVGVVVTXDRNSXTPZDKGDZERZ
KeyPos=4: LHHGXKWTBXHFMXXMHEHGAHXGXMZ
KeyPos=5: TOBGMNSLMOTTHVTGMNMNDEQRRLG
My idea was to calculate the highest-frequency letter in each block, hoping that the most frequent letter would give me some clue as to how to find 'U,' 'A' and 'R.' However, the most frequent letters in these blocks are:
KeyPos=0: Q,4 T,3 E,3, J,3
KeyPos=1: C,4 U,3 Y,3
KeyPos=2: N,4 O,3 R,3 D,3 B,2
KeyPos=3: V,4 D,3 Z,3
KeyPos=4: H,6 X,6 M,3 G,3
KeyPos=5: M,4 T,4 N,3 G,3
Which yields QCNVHM, or QUNVHM (being generous), neither of which are that close to QUARTZ. There are online applets that can crack this no problem, so it mustn't be too short a text to yield decent frequency counts from the blocks.
I guess I must be approaching this the wrong way. I just hoped one of you might be able to offer some clue as to where I am going wrong.
p.s. This is for a digital crypto class.
Interesting question...
I don't have a programmatic solution for cracking the original ciphertext, but I was able to solve it with a little mind power and some helpful JavaScript.
I started by using this page and the information you supplied. Provide the ciphertext, a key length of 6 and hit initialize. What's nice about the approach here is that unknowns in either the plaintext or key are left as hyphens.
Update the key, adding only what you know Q---TZ and click 'update plaintext'. At this point we know:
o---sua---opo---oca---nha---enc---rom---dth---ama---int---ept---our---mun---tio---ewi---eus---the---ond---loc---onf---now---hed---off---ere---nsw---esd---tmi---ght
Here's where I applied a bit of brain power. You start recognizing bits of the plaintext. the, now and off make an appearance. At the end, there's ght - this made me think the prior letter is likely a vowel. For example light or thought. I replaced the corresponding hyphen with u and clicked update keyword to find what letter would have produced that combination. The matching letter turns out to be F. I think updated the plaintext to see the results. They didn't look promising. So I tried i instead which resulted in:
o--usua--ropo--loca--onha--eenc--prom--edth--eama--eint--cept--gour--mmun--atio--wewi--beus--gthe--cond--yloc--ionf--mnow--thed--poff--mere--insw--nesd--atmi--ight
Now we're getting somewhere. At the start I see something that might be usual, and further in I see int--cept and near the end w--nesd-- at mi--ight. Voila. Filling in the letters for wednesday and updating the keyword yielded QUARTZ.
... So, how to port this approach to code? Not sure about the best way to do that just yet. The idea of using the known characters in the key, partially decrypting the ciphertext and brute forcing the rest is appealing. But without a dictionary handy, I'm not sure what the best brute-forcing method would be...
To be continued (maybe)...
An algorithm wouldn't just consider the most frequent letters but the frequency pattern of the whole alphabet. Technically you compute the index of coincidence for each possible shift and consider the maximal ones.
Well I have been working on an assigment and it states:
A program has to be developed, and coded in C language, to decipher a document written
in Italian that is encoded using a secret key. The secret key is obtained as random
permutation of all the uppercase letters, lowercase letters, numbers and blank space. As
an example, let us consider the following two strings:
Plain: “ABCDEFGHIJKLMNOPQRSTUVXWYZabcdefghijklmnopqrstuvwxyz0123456789 ”
Code: “BZJ9y0KePWopxYkQlRjhzsaNTFAtM7H6S24fC5mcIgXbnLOq8Uid 3EDv1ruVGw”
The secret key modifies only letters, numbers, and spaces of the original document, while
the remaining characters are left unchanged. The document is stored in a text file whose
length is unknown.
The program has to read the document, find the secret key (which by definition is
unknown; the above table is just an example and it is not the key used for preparing the
sample files available on the web course) using a suitable decoding algorithm, and write
the decoded document to a new text file.
And I know that I have to upload an English dictionary into the program but I don't why it has been asked (may be not in that statement but I have to do THAT). My question is, while I can do that program using simple encryption/decryption algorithm then what's the use of uploading the English dictionary in our program? So is there any decryption algorithm that uses a dictionary to decrypt an encrypted algorithm? Or can somebody tell me what approach or algorithm should I use to solve that problem???
An early reply (and also authentic one) will be highly appreciated from you.
Thank you guys.
This is a simple substitution cipher. It can be broken using frequency analysis. The Wikipedia articles explain both concepts thoroughly. What you need to do is:
Find the statistical frequency of characters in Italian texts. If you can't find this published anywhere, you can build it yourself by analyzing a large corpus of Italian texts.
Analyze the frequency of characters in the cipher text, and match it to the statistical data.
The first Wikipedia article links to a set of tools that implement all of the above. You just need to use and possibly adapt it to your use case.
Your cipher is a substitution cipher. That is it substitutes one letter for another.
consider the cipher text
"yjr,1drv2ry1od1q1..."
We can use a dictionary to find the plaintext.
Find punctuation, since a space always follows a comma, you can find the substitution rule for spaces.
which gives you.
"yjr, drv2ry od q..."
Notice the word lengths. Since there only two 1 letter words in the english language the q is probably i or a. "yjr" is probably "why", "the", "how" etc.
We try why with the result
"why, dyv2yw od q..."
There are no english words with two y's, and end in w.
So we try "the" and get
"the, dev2et od q..."
We conclude that the is a likely answer.
Now we search our dictionary for words that start look like ?e??et.
rinse repeat.
That is, find some set of words which fit into the lengths available and do not break each others substitution rules.
Personally I just do the frequency analysis suggested above.
Frequency analysis, as both other respondents said, is the way to go, and you can use digrams and trigrams to make it much stronger. Just grab tons of Italian text from the web and churn ahead! It's really pretty simple programming.