Showing posts with label crytography. Show all posts
Showing posts with label crytography. Show all posts

Beginner Guide to Classic Cryptography

Cryptography:  It is a technique of scrambling message using mathematical logic to keep the information secure. It preserve the scrambled message from being hacked when transport over unsecure network. Since it convert the readable message in unreadable text.

Plaintext: It is the content of data which is in readable form that need to share over insecure network.
Encrypting key: It is random string of bits created particularly to scramble the plaintext information into unreadable text using mathematical logic. There are two types of encryption key symmetric key and asymmetric key.

Cipher text: The output of encryption produce cipher text which in not readable by human beings.

Decrypting key: It is the key which use to decipher the cipher text into again plaintext using symmetric or asymmetric key to read original message

Functionality of cryptosystem

·         Authentication: It is the process of verification of the identity of the valid person through his username and password that communicates over a network.
·         Authorization: It refers to the process of granting or denying access to a network resource or service. Most of the computer security systems that we have today are based on a two-step mechanism. The first step is authentication, and the second step is authorization or access control, which allows the user to access various resources based on the user’s identity.
·         Confidentiality or privacy: It means the assurance that only authorized users can read or use confidential information. When cryptographic keys are used on plaintext to create cipher text, privacy is assigned to the information.
·         Integrity: Integrity is the security aspect that confirms that the original contents of information have not been altered or corrupted. There should be not any kind of modification with information while it transport over network.
·         Non repudiation: Non repudiation makes sure that each party is liable for its sent message. Someone can communicate and then later either falsely deny the communication entirely or claim that it occurred at a different time, or even deny receiving any piece of information.

Classical Cryptographic Algorithms types
Caesar cipher
Caesar cipher is a type of substitution cipher in which each letter of the alphabet is swap by a letter a certain distance away from that letter.
Step 0: Mathematically, map the letters to numbers (i.e., A = 1, B = 2, and so on).

Step 1: Select an integer key K in between 1 and 25 (i.e., there are total 26 letters in the English language) let say shift right 3 alphabets where A +3 = D, B+3 = E and so on.

Step 2: The encryption formula is Add k mod 26; that is, the original letter L becomes (L + k)%26.
For example encryption of “IGNITE” will like as:
C = E (L+K) %26
Here L= I and K = 3
C = E (I+3) % 26
C = E (9+3) % 26
C = E (12) % 26
C = E (L)
Hence encryption of IGNITE: LJQLWH

Step 3: The deciphering is “Subtract k mod 26”; that is, the encrypted letter L becomes (L k) %26.
For example Decryption of “LJQLWH” will like as:
C = D (L-K) %26
C = D (L-3) % 26
C = D (12-3) % 26
C = D (9) % 26
C = D (I)
Hence decryption of LJQLWH: IGNITE

Limitation: Caesar cipher is vulnerable to brute-force attack because it depends on a single key with 25 possible values if the plaintext is written in English. Consequently, by trying each option and checking which one results in a meaningful word, it is possible to find out the key. Once the key is found, the full cipher text can be deciphered accurately.

Monoalphabetic Cipher

It is also a type of substitution cipher in which each letter of the alphabet is swap by using some permutation of the letters in alphabet. Hence permutations of 26 letters will be 26! (Factorial of 26) and that is equal to 4x1026. This technique uses a random key for every single letter for encryption and which makes the monoalphabetic cipher secure against brute-force attack.

The sender and the receiver decide on a randomly selected permutation of the letters of the alphabet. For example in word “HACKING” replace G from “J” and N from “W” hence permutation key is 2! i.e. factorial of 2 and HACKING will become “HACKJIW”.

Step 0: Generate plaintextcipher text pair by mapping each plaintext letter to a different random cipher text letter IJKLQR--------GFE.

Step 1: To encipher, for each letter in the original text, replace the plaintext letter with a cipher text letter.
Hence encryption of “IGNITE” will be as shown below:

Step 2: For deciphering, reverse the procedure in step 1.
Hence decryption of “USBUOQ” will be “IGNITE”

Despite its advantages, the random key for each letter in monoalphabetic substitution has some downsides too. It is very difficult to remember the order of the letters in the key, and therefore, it takes a lot of time and effort to encipher or decipher the text manually. Monoalphabetic substitution is vulnerable to frequency analysis.

Playfair Cipher

It encrypts digraphs or pairs of letters rather than single letters like the plain substitution cipher
In this cipher a table of alphabet is 5x5 grids is created which contain 25 letters instead of 26. One alphabet “J” (or any other) is omitted. One would first fill in the spaces in the table with the letters of the keyword (dropping any duplicate letters), then fill the remaining spaces with the rest of the letters of the alphabet in order. If the plaintext () contains J, then it is replaced by I.

Step 0: Split the plaintext into pair, if number of letters are odd then add “X” with last letter of plaintext
For example “TABLE” is our plaintext split it into pair as: TA BL EX
Step 1: Set the 5 × 5 matrix by filling the first positions with the key. Fill the rest of the matrix with other letters. Let assume “ARTI” is our key for encryption.

Step 2: For encryption it involves three rules:
If both letters fall in the same row, substitute each with the letter to its right in a circular pattern. TA-----> IR

(1)    If both letters fall in the different row and column, form a rectangle with the two letters and take the letters on the horizontal opposite corner of the rectangle. BL-----> TN

(1)    If both letters fall in the same column, substitute each letter with the letter below it in a circular pattern. EX-----> LT

Hence encryption of word “TABLE” is “IR TN LT”.
Step 3: For decryption receiver use same key to decipher the text by reversing above three rules used in step 2.

Playfair is considerably complicated to break; it is still vulnerable to frequency analysis because in the case of Playfair, frequency analysis will be applied on the 25*25 = 625 possible digraphs rather than the 25 possible monographs (monoalphabetic)

Polyalphabetic Cipher

A polyalphabetic substitution cipher is a series of simple substitution ciphers. It is used to change each character of the plaintext with a variable length. The Vigenere cipher is a special example of the polyalphabetic cipher.

Step 0: Decide a encrypting key to change plaintext into cipher, for example take “HACKING” as encryption key whose numerical representation is “7, 0 ,2 ,10, 8, 13, 6 “

Step 1: To encrypt, the numeric number of first letter of the key encrypts the first letter of the plaintext, the second numeric number of second letter of the key encrypts the second letter of the plaintext, and so on.
For example plaintext is “VISIT TO HACKING ARTICLES” and key is “HACKING: 7 0 2 10 8 13 6”

Step 2: The encryption formula is “Add k mod 26”; that is, the original letter L becomes (L + k)%26
C = E (L+K) %26
Here L=V and K =7
C = E (V+7) %26
C = E (21+7) %26
C = E (28) %26
C = E (2)
C = E (C)

Step 3: The deciphering is “Subtract k mod 26”; that is, the encrypted letter L becomes (L k) %26.
For example Decryption of “CIUSBGUOAEUQAMHRVSKYKZ” will like as:
C = D (L-K) %26
Here L=C and K =7
C = E (C-7) %26
C = E (21)
C = E (V)

The main limitation of the Vigenère cipher is the repeating character of its key. If a cryptanalyst properly estimate the length of the key, then the cipher text can be treated as link Caesar ciphers, which can be easily broken separately.

Rotation cipher
In rotation cipher generates cipher text on the behalf of block size and angle of rotation of plain text in the direction of following angles: 90o 1800 270

Step 0: Decide the size of block for plaintext “CRYPTOGRAPHY”, let assume 6 as block size for it.


Step 1: For encryption arrange plaintext in any direction among these angles 90o 1800 270o   as shown below:
·         In 90o Rotation place starting letter downwards vertically from G to C and so on.


·         In 180o Rotation place letter right to left horizontally from O to C and so on.


·         In 270o Rotation place last letter top to bottom vertically from O to Y and so on.

Hence cipher text will arrange in following ways:

Step 2: arrange letter according their angles represents:
90 rotated cipher “GCRRAYPPHTYO”
180 rotated cipher “YHPARGOTPYRC”
270 rotated cipher “OYTHPPYARRCG”

Step 3: for decryption using block size and angle of rotation among all above three cipher texts can be decrypt.

Transposition cipher
In transposition cipher plaintext are rearrange without replacing original letter from other as compare to above cipher techniques.


Step 0: Decide the keyword that will be represent the number of column of a table which store plain text inside it, and help in generating cipher text, let suppose we choose CIPHER as key.
Step 1: store plaintext “classical cryptography” in a table from left to right cell.

Step 2: for encryption arrange all letters according to columns from in ascending order of keyword “CIPHER” will be CEHIPR as:

Column 1: CCCPP
Column2: ESRR
Column 3: HSCG
Column 4: PALOY
Column 5: RIYA
Hence the cipher obtain will be “CCCPPESRRHSCGPALOYRIYA
Step 3: for decryption receiver use key to rearrange 26 cipher letters according to its column in 6*5 matrix.

It was very easy to rearrange cipher letter if correct key is guesses.

Rail fence cipher

The 'rail fence cipher' also called a zigzag cipher is a form of transposition cipher the plain text is written downwards and diagonally on successive "rails" of an imaginary fence, then moving up when we reach the bottom rail. 

Step 0: choose the number rails which will act as key for plotting the plaintext on it. Here 3 rails is decided as key for encryption
Step 1: plot plaintext “RAJ CHANDEL” on the rail in zigzag form, in direction top to bottom (downwards and diagonally) and then bottom to up (upwards and diagonally)

Step 2: for encryption place all letter horizontally starting form row 1 to row 3 as:
Row 1: RHE
Row 2: ACADL
Row 3: JN
Hence encryption for “RAJCHANDEL” is “RHEACADLJN”

Step 3: for decryption generate the matrix by multiplying total cipher text with number of rail, here
Total 10 letters are in cipher text “RHEACADELJN” and 3 rails, hence matrix will of 10*3.

 Transverse the above rule use in encryption and place the cipher text as

Row 1: RHE

Row 2: ACADL

Row 3: JN

The rail fence cipher is not very strong; the number of practical keys (the number of rails) is small enough that a cryptanalyst can try them all by hand.

Understanding HTTP Authentication Basic and Digest

HTTP authentication uses methodologies via which web servers and browsers securily exchanges the credentials like user names and passwords. Http authentication or we can also call it as Digest Authentication follows the predefined methods / standards which use encoding techniques and MD5 cryptographic hashing over HTTP protocol.

In this article we are covering the methodologies/standards used for Http Authentication.

For the sake of understanding we will be using our php scripts that will simply capture user name and passwords and we will generate the Authorization value as per the standards.

For http codes visit here

Basic Access Authentication using Base 64 Encoding

In basic Authentication we will be using base 64 encoding for generating our cryptographic string which contains the information of username and password. Please note we can use any of the encoding techniques like URL, Hexadecimal, or any other we want.

The below example illustrates the concept, we are using Burpsuite for capturing and illustrating the request.

The webpage is asking for input from the client

We are providing "hackingarticles" as User Name and "ignite" as password.

Syntax of basic Authentication
 Value = username:password
Encoded Value =  base64(Value)
Authorization Value = Basic  

In basic authentication username and password are combined into a single string using a colon in between.
Value =  hackingarticles:ignite

This string is then encoded using base 64 encoding.

Encoded Value = base64 encoded value of hackingarticles:ignite which is aGFja2luZ2FydGljbGVzOmlnbml0ZQ==

Finally the Authorization Value is obtained by putting the text "Basic" followed by before the encoded value. (We can capture the request using burpsuite to see the result)

The Authorization Value for this example is "Basic aGFja2luZ2FydGljbGVzOmlnbml0ZQ==" . This is the value which is sent to the server.  

Finally the server is decrypting the authorization value and returning the entered credentials

Basic Authentication is less secure way because here we are only using encoding and the authorization value can be decoded, In order to enhance the security we have other standards discussed further.

RFC 2069 Digest Access Authentication

Digest Access Authentication uses the hashing methodologies to generate the cryptographic result. Here the final value is sent as a response value.
RFC 2069 authentication is now outdated now and RFC2617 which is enhanced version of RFC2069 is being used. 

For the sake of understanding the syntax of RFC 2069 is explained below.

Syntax of RFC2069

Hash1 contains the MD5 hash value of (username:realm:password) where realm is any string
provided by server and username and passwords are the input provided by client.

Hash2 contains the MD5 hash value of (method:digestURI) where method could be get or post depending on the page request and digestURI is the URL of the page where the request is being sent. 

response is the final string which is being sent to the server  and contains the MD5 hash value of (hash1:nounce:hash2) where hash1 and hash2 are generated above and nonce is an arbitrary string that could be used only one time provided by server to the client.

RFC 2617 Digest Access Authentication

RFC 2617 digest authentication also uses MD5 hashing algorithm but the final hash value is generated with some additional parameters

Syntax of RFC2617

Hash1 contains the MD5 hash value of (username:realm:password) where realm is any string
Provided by server and username and passwords are the input provided by client.

Hash2 contains the MD5 hash value of (method:digestURI) where method could be get or post depending on the page request and digestURI is the URL of the page where the request is being sent. 

response is the final string which is being sent to the server  and contains the MD5 hash value of (Hash1:nonce:nonceCount:cnonce:qop:Hash2) where Hash1 and Hash2 are generated above
and for more details on other parameters refer ""

The actual working of RFC2617 is described below

The webpage is asking for input from the client

We are providing "guest" as User Name and "guest" as password.

Through burpsuite we are capturing the request so that all the parameters could be captured and we can compare the hash values captured with the hash values that we will generate through any other tool (hash calculator in this case).

We have captured the values for the following parameters

realm="Hacking Articles", nonce="58bac26865505", uri="/auth/02-2617.php", opaque="8d8909139750c6bd277cfe1388314f48", qop=auth, nc=00000001, cnonce="72ae56dde9406045" , response="ac8e3ecd76d33dd482783b8a8b67d8c1",

Hash1 Syntax=MD5(username:realm:password)
hash1 =  md5(guest:Hacking Articles:guest)

The MD5 hash value is calculated as 2c6165332ebd26709360786bafd2cd49

Hash2 Syntax =MD5(method:digestURI)

MD5 hash value is calculated as b6a6df472ee01a9dbccba5f5e6271ca8

response Syntax =  MD5(Hash1:nonce:nonceCount:cnonce:qop:Hash2)
response = MD5(2c6165332ebd26709360786bafd2cd49:58bac26865505:00000001:72ae56dde9406045:auth:b6a6df472ee01a9dbccba5f5e6271ca8)

MD5 hash is calculated as  ac8e3ecd76d33dd482783b8a8b67d8c1

Finally the response value obtained through hash calculator is exactly same as that we have captured with burp suit above. 

Finally the server is decrypting the response value and the following is the result

Beginner Guide to Understand Hashing in Cryptography

Cryptography is conversion of plain readable text into unreadable form. In cryptography first the data is converted into cipher text (that is encryption) and then the cipher text is converted back into readable form (that is decryption). Cryptography basically works on the concept of encryption and decryption. Encryption and decryption should not be confused with encoding and decoding, in which data is converted from one form to another but is not deliberately altered so as to conceal its content. Encryption is achieved through the algorithms. These algorithms are works with logic, mathematic calculations and its complexities.
Hash Function is most important function in Cryptography. A hash means a 1 to 1 relationship between data. This is a common data type in languages, although sometimes it’s called a dictionary. A hash algorithm is a way to take an input and always have the same output, otherwise known as a 1 to 1 function. An ideal hash function is when this same process always yields a unique output. So you can tell someone, here is a file, and here is its md5 hash. If the file has been corrupted during then the md5 hash will be a different value.
In practice, a hash function will always produce a value of the same size, for instance md5 () is will always return 128bits no matter the size of the input. This makes a 1 to 1 relationship impossible. A cryptographic hash function takes extra precautions in making it difficult to produce 2 different inputs with the same output, this is called a collision. It also makes it difficult to reverse the function. Hash functions are used for password storage because if an attacker where to obtain the password's hash then it forces the attacker to break the hash before he can use it to login. To break hashes, attackers will take a word list or an English dictionary and find all of the corresponding hash values and then iterate though the list for each password looking for a match.
md5 (), sha0 and sha1 () are all vulnerable to a hash collision attacks and should never be used for anything security related. Instead any member of the sha-2 family, such as sha-256 should be used.
To calculate Hash Value, we will use Hash Calculator. Install Hash Calculator from -->
Hash function plays major role in hacking/forensic world because it helps us to know whether a particular file has changed or not. You can also calculate hash value of your computer and know if anyone has made any kind of changes.

To calculate hash value open Hash Calculator.

Now browse the file of which you want to calculate the hash value. And click on Calculate.

After clicking on calculate it will give too hash values using four different hashing algorithms i.e MD5, SHA1, RIPEMD160, CRC32. You can check other boxes too if you want to use those algorithms to calculate hash value.
This way Hash calculator helps us to know the hash value. Now if there are any changes made in this file, the hash value will change too.
Once I calculated the hash value above i made some changes in the file and calculated the hash value again with the same method and as a result the hash value was changed.

 Now, we have two hash values. Let us compare both of these values of MD5. The value of first file is 1110808875326e25dl93e4ee096afaf1 and the value of other file is fb9d53883f302d78c978a583e8a85.
Seeing these two values of MD5 of the same file we can conclude that some changes are made. Because even slightest difference will change the hash value.
But now the main question is how to detect this change because a file can be of 1TB too. Also imagine that you are sending a harddisk full of important documents to someone and there is a huge possibility that someone can bribe the sender and make changes in your documents. So how can you detect these changes?
The answer is very simple --> Compare it! This tool helps us achieve our goal which is to detect the change.
Download Compare it! From -->
Open Compare it!

Click file and a drop menu will appear. Select compare files option.

A Dialogue box will open which will ask you to choose the files that you want to compare. Click on Browse button and select your file. And click on Open.

It will show you the changes by highlighting them with green color and the red color will tell the exact change as shown below:

So, in such way you can protect your sensitive data and detect the crime done too.