Cryptography And Network Security

Critical review of the encryption / decryption techniques

Describe about the Cryptography and Network Security?

Cryptography is a coordinated documented which obtains ideas from arithmetic, gadgets and programming. Cryptography has been practiced from historic times starting from when Julius Caesar sent messages to the generals by means supplanting each letter set with 3 bits ahead letters in order like E is supplanted with H, C with F et cetera. The intention was to convey the message securely without being known not and even the detachment (Singh, Pal and Bhatia 2013). Therefore, the principle reason for existing was to store the data securely, pass it securely and along these lines keep it from assaults.

This section critically analyzes and reviews several encryption / decryption techniques with a thorough explanation of how each of the technique works as well as evaluation of their individual strengths and weaknesses, properties and characteristics (Bauer 2013).

In this particular technique, cipher text letters usually replace a particular plaintext. A fixed replacement structure determines the monoalphabetic substitution. To be more precise, if a particular letter such as an ‘e’ is replaced with ‘M’; it means that all of e’s in that particular document will always be replaced only by ‘M’. The main concept behind this technique is a permutation of particular alphabets (Goyal and Kinger 2013). Inverse permutation is to be used for the decryption technique of the encrypted or ciphered text.

The mathematical description of this technique is discussed below:

If S (E) were a collection of symmetrical permutations, a monoalphabetic substitution would be f_σ(a₁.  . .a_r) := (σa₁, . . . , σa_r) for (a1, . . . , a_r) ∈Σ^r

The general approach: The invariants are the distribution of frequencies of different and individual letters or alphabets or characters. Repeated patterns also significantly appear in the encrypted or ciphered text. This particular variant of cryptographic procedure is dependent upon replacing one single character with a particular and fixed character (Heydari, Shabgahi and Heydari 2013). The cryptanalysis of the Monoalphabetic substitution makes use of its invariants, which is of properties of substance that stay unaltered under encryption:

Single characters or alphabets and the corresponding allocation of it is invariant. The alphabet or character content happens exactly the equal number of times as the contrasting characters in the plain text. Irregular plans in the plaintext show up furthermore in the figure content.

Just in unprecedented situations, cryptanalysis is exceptionally algorithmic (Huang 2015). Despite of that, it can be implied that framework implements the degree to which it can be determined how clear is its theoretical reason is, the successful game plan validates the cryptanalyst.

One of the main advantages of monoalphabetic substitution is it is comparatively simple, easily comprehensive and implementation is easy. The number of possible keys is (26!) which significantly reduces the impact of brute force attacks (Jain, Dedhia and Patil 2015). To be more precise the exact number of keys involved in this type of cryptographic technique is 4 x 10²⁶.

The weakness of monoalphabetic substitution process is its language characteristics. By nature, human languages tend to be significantly redundant. There are certain letters that are most commonly used such as S, O, N, R, A, T or I (Kahate 2013). On the contrary, there are certain letters that are used comparatively rarely such as Z, Q, K, J or Q.

Monoalphabetic substitution techniques

Figure 1: English letter frequencies

(Source: Kuppusamy, Pitchai Iyer and Krithivasan 2014)

Therefore, monoalphabetic ciphers do not provide 100 % security and thereby can be cracked quite easily using statistical methods, such as shown above.

Cesar cipher is one of the sub procedures that fall under monoalphabetic cipher texts. It consists of a very simple and comprehendible and thereby it is quite easy to crack or break the encrypted message or ciphered text (McGrew et al. 2014). This algorithm or technique has such a name because Julius Caesar originally used it.

The fundamental approach for ‘encryption’ applied in this technique involves creating the ciphered text alphabet  by left – shifting the particular alphabets using the accurate the number of places as demonstrated by the key being used (Mekhaznia and Menai 2014).

On the contrary, the decryption process similarly involves a significantly simple and comprehensive process that only associates itself with the corresponding letter of the cipher text. However, it is to be noted that, although the key may be unknown, breaking the code can be easy if it is known that shift cipher is applied for that particular purpose (Mohan, Devi and Prakash 2015). It is most possibly the first known substitution cipher used and attested in military activities. The main idea lying behind this technique is to replace each letter with the third letter. The main mathematical calculation can be represented as:

c = E (k, p) = (p + k) mod 26

p = D (k, c) = (c – k) mod 26

The strengths or advantages of Caesar shift cipher are described below:

It focuses on mapping alphabets in permutations randomly, rather than simply shifting the alphabets or characters.

The fundamental weakness of Cesar cipher is it is comparatively easy to break mainly because of its simple nature. It is not that strong in terms of the security aspects provided by it (Mozaffari-Kermani et al. 2014). Normally utilized letters like “e” show up rapidly as the “x” in the illustration. Words with rehashed letters like “meet” in the case demonstrate that reiteration in the cipher text. What’s more, in reality this is weak to the point that the day-by-day cryptogram keep running by a few daily papers is ordinarily a Cesar shift substitution.

Transposition cipher is a commonly used type of cryptographic (encryption / decryption) technique (Nema and Jain 2013). The algorithm for transposition technique involves the following steps:

Step 1: the first step deals with selecting a proper password

Step 2: the plain text is required to be known

Step 3:It is required to draw a table with matching number of columns with the exact number of alphabets; the number of rows should be adequate for accommodating the alphabets or characters involved in the plain text (Othman, Hassoun and Owayjan 2015).

Step 4: The fourth steps requires arranging the password so as to the accurate number of appearance of the alphabet with respect to the letter ‘a’ is to be assigned in the beginning of the position no matter what column it is.

Method

Step 5: The position of the alphabet in the respective columns is required to be understood for continuing the process until the password position has been covered fully (Pachghare 2015).

This process, when executed in reverse is referred to as decryption.

There are numerous different approaches to transpose messages than columnar transposition utilizing squares and rectangles. The state of the geometric figure utilized can be shifted, and the technique for engraving and removing content can be differed (Pommerening 2014). Columnar techniques are the most normal in military utilization, since they are the simplest to learn and utilize dependably, be that as it may, different techniques might be experienced. Some of these normal techniques are appeared underneath.

Transposition can be utilized to create a mixed request of the letters in the letter set for use as a substitution letters in order (Pommerening 2014).

Transposition frames part of a portion figure, where letters are partitioned into parts, then the parts are assembled in an alternate request, fitting in with various letters.

This arrangement relied on upon accurately distinguishing the width of the network and the lucky appearance of the Q and U (Rueppel 2012). Without the Q and U and with no sign of the width, significantly more experimentation would be required for an effective arrangement.

The section explains the encryption and decryption procedures applied for columnar transposition cipher (Sharma et al. 2013). The steps for encryption in columnar transposition are discussed below:

Step 1: The password is set

Step 2: ASCII code is to be yielded by converting the alphabets included in the password. The first alphabet in the original word or sentence can be easily found replacing with the largest ASCII value  

Step 3: This step focuses on finding out the accurate length of the plain text

Step 4: The determination of the exact number of rows is based on the length of the plain text and the length of the password combined (Shrivastava, Sharma and Chouhan 2013). The number of column should be known beforehand from the number of letters in the password.

Step 5: The rows not entirely filled using the characters are completed with applying exceptions.

Step 6: The step 4 determines the size of array depending upon which the arrangement of the plain text is performed (Singh, Pal and Bhatia 2013).

Step 7: The columns should be positioned as an according to the step 2.

Step 8: This is the final step from which the encrypted message is received.

Key: 4 1 2 3 5

Plaintext: d a t a

e n c r y          

p t i o n

Cipher text: anttciarodep yn

Most transposition frameworks improve content by single letters. It is conceivable to revise complete words or gatherings of letters as opposed to single letters, yet these methodologies are not exceptionally secure and have minimal handy worth. Bigger gatherings than single letters protect a lot of unmistakable plain content.

Columnar transposition frameworks can be misused when keys are reused with messages of the same length (Shrivastava, Sharma and Chouhan 2013). The plain content to messages with reused keys can frequently be recouped without respect to the real strategy for enciphers. Once the plain content is recuperated, the strategy can be recreated.

Strengths

The rail fence is a simple to apply transposition that scatters up the request of the letters of a message in a speedy helpful manner. It likewise has the security of a key to make it a smidgen harder to break.

The Rail Fence figure works by composing your message on interchange lines over the page, and afterward perusing off every line thusly (Singh and Manimegalai 2015). For instance, the plain content is composed as demonstrated as follows, with all spaces uprooted.

Rail fence technique is reading so as to be decoded it in masterminding it in segments or columns before understanding it (Van Tilborg and Jajodia 2014). Along these lines, it is very much a simple and quick procedure, and it is less inclined to botches.

One of the issues that this type of technique faces is that the security of the code is dependent on the way that a cryptanalyst does not know the technique for encryption (Singh and Manimegalai 2015). Henceforth, once the technique for encryption is broken, the code is broken as of now.

Another issue with this type of technique is that is not exceptionally solid. This implies the quantity of conceivable arrangements is small to the point that a cryptanalyst can attempt all of them by hand (Singh and Johari 2015). Consequently, the rail wall figure is anything but difficult to break as we just need to test all the conceivable divisors up to a large portion of the length of the content.

It is another type of transposition technique in use for many years. The fundamental aspect lies in choosing the length of permutation and thereafter, the key becomes the random permutation (Singh and Johari 2015). It is not similar to monoalphabetic ciphers.

The Permutation Cipher is harder to break with a cipher text-just assault. In any case, it succumbs effortlessly to a known plaintext assault. Truth be told, if one knows plaintext and cipher text, then it is not troublesome for him to decide the length m and after that locate the key π (Singh 2014). In spite of the fact that the Substitution Cipher and the Permutation Cipher is not secure, they are imperative components in cutting edge cryptosystems.

Break the plaintext up into groups of a fixed size, d

define a permutation of the integers 1 to d called f

within each block, permute the letters according to f

the key is (d, f)

For example, let d = 5 and let f is given by:

1 ——— 3

2 ———- 4

3 ——– 1

4 ——- 5

5 ——— 2

The primary strength of this cipher is that is difficult to break as compared to the other cipher procedures (Van Tilborg and Jajodia 2014).

However, permutation cipher is not hundred percent secure.

The researcher study about three types of encryption technique namely, substitution cipher, transposition cipher and permutation cipher. The researcher finds that the rail fence technique is the simplest technique, which can be crack easily. The rail fence technique is a transposition cipher. Here the transposition is based on rearranging total text either typographical or mathematical; the output of this arranging is called cipher (Singh and Johari 2015). The rail fence technique uses a zigzag pattern to encrypt the plaintext. Here the programmer performs a test of a rail fence technique but the generated output is very simple. Thus, this cipher text can be crack easily, even it can be solve with a pen and paper.

Weaknesses

Here one example of the rail fence techniques is described with the basic concept of encryption. If the plain text is, “DEFEND THE EAST WALL OF CASTE”. Than the cipher, text will produce as follows (here the value of key is 3):

Than the program read this line along the row and a string variable collect the total character set (Singh 2014). Here the researcher encrypts this text a find the following set of text as a cipher test.

From the above example, the programmer identify that it is not a right choice to encryption a plaintext. Now the programmer identify that the substitution and transportation cipher techniques are pretty much similar and easy to crack (Van Tilborg and Jajodia 2014). Therefore, the programmer choose the permutation cipher as an encryption stranded to encrypt a plain text, because this is more complex to crack than other techniques.

The programmer chose the permutation cipher to encrypt the plain text. The permutation cipher is similar to the columnar transformation is some ways, here the method of permutation is acts on blocks of latter instead of the selecting the entire cipher text. In mathematical concept the permutation is perform by rearranging the set of elements. In this program, every word is shifted to the left, but the shift order is depend on the key (Rueppel 2012). For an instance, the order of the plain text is {“Day1”,”Day2”,”Day3”}, than after the permutation is seems like that { “Day2”,”Day3”,”Day1”}. Here the programmer chooses a keyword of length 3 than this program spilt this plain text according to the keyword length. Here the programmer demonstrated this in the following example.   

               

Figure 2: The plain text and the permutated text

(Source: Pachghare 2015)

The above section demonstrated the encryption process of the permutation cipher, here the programmer define the method of conversion of encrypted text to plain text. As the encryption method use keyword length to split the plain text here decryption also use same concept to split the text. At first, the order of the keyword is set at the top of the columns. Than the programmer set the method to rearrange the cipher text according to this order, and read the plain text row wise (Othman, Hassoun and Owayjan 2015). For better understanding of decryption technique the programmer this process with an example, is given underneath. Let’s take the keyword length is 5, and set the cipher text according to their order row by row (figure).

Figure 3: Representing the cipher text row by row.

(Source: Sharma et al. 2013)

Now the program record the letters of the keyword to form original keyword, and similarly the program rearrange the elements in the same way. Here the recoded grid is showing in below figure.

Figure 4: The recorded grid.

(Source: Mohan, Devi and Prakash 2015)

The encryption algorithm:

Step 1: the keyword is in the small alphabet.

Step 2: the keyword is converted in ASCII value. It provides simplest way to find the alphabet comes first.

Cesar shift cipher

Step 3: in this step, the plaintext length is found.

Step 4: The length of the secret key and the length of the plaintext is utilized to decide the quantity of lines that will be made as the quantity of section is as of now known as the quantity of the keyword characters (Kahate 2013).

Step 5: here the rows are completed by the exception.

Step 6: according to the step 4, the plaintext is arranged.

Step 7: according to the step 2, the columns are readied.

Step 8: it prints the encrypted text and print it. Execute the previous steps 1 to 7 again.

The permutation cipher is implemented in java; here the programmer provides the evidence of successfully execution program and its outcome. Here the programmer uses the NetBeans framework to implement this application (Huang 2015). The input of the application is taken plaintext from the user and it provides cipher text. After generating the cipher text the program also decrypt this message and, generate the plain text.

Figure 5: Taking plaintext from user

(Source: created by authod)

Figure 6: Print the encrytion and dycryption text

(Source: The texing Table)

The testing table:

Test No	Text size	File size	Expected outcomes	Encryption outcomes	Decryption Outcomes	Encryption Time Span	Decryption TimeSpan	Cipher Key	Key size
1	8	5 bytes	Correctly encrypted	Successful	Here the programmer try to encrypt the plain text	0.01000	0.01701	megabuck	8 bit
2	8	20 bytes	Correctly encrypted	Successful	Here the programmer try to encrypt the plain text	0.02900	0.11400	megabuck	8 bit
3	8	16 bytes	Correctly encrypted	Successful	Here the programmer try to encrypt the plain text	0.00900	0.01400	megabuck	8bit

Conclusion

The motivation behind encryption and unscrambling is to guarantee those messages imparted between two elements are sheltered and secure from any sort of digital or system assault. Encryption and unscrambling guarantees that message begin from the approved sender and decoded by legitimate recipient. Subsequently the investigation of different strategies to camouflage messages or content with a specific end goal to stay away from its capture attempt from unapproved client is known as cryptography. To guarantee the wellbeing in correspondence cryptography and its procedures are utilized. There are numerous encryption and unscrambling strategies accessible however; these techniques have their own focal points and inconveniences. In this work I proposed an exceptionally basic however viable symmetric key encryption strategy.

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