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.
Related
I am searching for a simple code that encrypt a random number and letters with cipher shift. Example: -3 abcdefghijklmnopqrstuvwxyz output xyzabcdefghijklmnopqrstuvw
Be aware, that this is no encryption.
You are simply obfuscating the input. But this is being revealed quite easily.
Your question itself is very ambiguous. In what language do you want to look for? Please ask questions more specific.
Furthermore you could have look onto wikipedia:
https://en.wikipedia.org/wiki/Caesar_cipher
This is what you want to do. The code itself comes with the language.
Best,
Bent
This is about Enigma encryption, I'm guessing the number of rotors doesn't matter but I'm using 3.
I am working with what's basically a coded version of the old mechanical enigma style encryption machines. The concept is rather old but before I get too far into learning it, I was wondering if it would be possible to be able to encrypt using all characters 0-9 a-z and A-Z but the encrypted text itself will only be a subset of these characters? I'm trying to replace a subset of characters (around 10 total) from the encrypted output, while still being able to get back to those characters if they were part of the input?
You can disambiguate by adding 1 to 2-character mapping for ambiguous symbols: O -> A1; 0 -> A2; other ambiguous symbols; A->AA. This is basically just like escaping in strings: we usually can’t put new line inside the string, so we represent it as \n. \ is represented as \\
If you’re working with encrypted data (so the probabilities of all characters are uniformly distributed and characters cannot be predicted) then you can’t compress the ciphertext. If you can compress it, then you’ve noticed some kind of pattern in the text and partially broken the encryption.
If you want to reduce the ciphertext’s alphabet, then you must increase the length of the ciphertext, otherwise you’ve successfully compressed it.
Hello everyone,
In one of projects I've found that data encrypts with algorithm I have never meet before. It converts input string to 10-symbol numeric string. It's definitely not one of popular hashes (md5, sha1, etc) or check sums (crc16, crc32, etc), I've checked all I known.
Example:
Input string: "davidc"; Output string: "2172453193".
Length of output string is fixed - 10 symbols. It contains only digits ("0123456789"). This is all details i can add =/
Maybe someone met something similar to that or maybe know algorithm - You'll economy lot of my time.
With love <3
I am working on encryption & decryption of data using AES-CCM.
While studying AES, I came across a word called S-Box.
What is S-Box, and the relationship with AES? How can it be calculated? Is it depends on symmetric key or not?
How will cypher text be generated in AES-CCM 128 bit?
The S-Boxes are a system that is used in symmetric cryptographic algorithms to substitute and obscure the relationship between the key and the text that you want to cypher.
You can see more in this article. Here, you have a part:
There are different types of cyphers according to their design [68]. One of these is the Substitution–PermutationNetwork (SPN) that generates the ciphered text by applying substitution and permutation rounds to the original text and the symmetric key to create confusion. To do this, it must be used the Substitution boxes (S-boxes) and Permutation boxes (P-boxes). The S-boxes substitute one-to-one the bits of a block of the input text in the round with bits of the output text. This output is taken as an input in the P-boxes and then it permutes all the bits that will be used as S-box input in the next round.
As #CGG said, S-boxes are a component of a Substitution-Permutation Network. The Wikipedia entry has good diagrams which will help explain how they work.
Think of an S-box as a simple substitution cipher -- A=1, B=2, etc. In an SPN, you run input through an S-box to substitute new values, then you run that result through a P-box (permutation) to distribute the modified bits out to as many S-boxes as possible. This loop repeats to spread the changes throughout the entire cipher text.
In general, an S-box replaces the input bits with an identical number of output bits. This exchange should be 1:1 to provide invertibility (i.e. you must be able to reverse the operation in order to decrypt), should employ the avalanche effect (so changing 1 bit of input changes about half the output bits), and should depend on every bit of input.
What i mean by this is that if i create a Lua program that randomly assigns numbers and letters to a three digit code wouldn't this code then be almost unbreakable(like if someone that wasn't supposed to got it) unless you have the program? sorry if this was already asked could some1 direct me to it.
Simple encryption is not used because it is not sufficiently secure. We use a level of encryption necessary to meet the required security level to successfully defend against attackers.
Attackers range from a curious friend to nation states, think the NSA, GCHQ, KGB & etc.
"Schneier's Law": Anyone, from the most clueless amateur to the best cryptographer, can create an algorithm that he himself can't break.
What you are describing is a called a substitution cipher.
These are broken by using frequency analysis. Because each letter and number is always assigned to the same code, letters in the input will lead to the corresponding codes appearing in the output with the same frequency. The cryptanalyst will study the kinds of data he expects to be input to the cipher, and find common symbols and patterns, then match those with frequent patterns in the output. For example, if the input is English text, the cryptanalyst knows that the most frequent codes represent E, T, A, O, I, … and the most common sequences are "THE", "BE", "OF", "AND", etc.
Codes in the output should occur with uniform probability. When there is a bias in the output, it can be exploited to break the code. One way to avoid this, in basic terms, is to use a different "code book" for each letter in the input. So "E" doesn't always translate to the same code; it would depend on the position of the "E" in the message.