Encryption of text characters using ASCII values

Encryption of text characters using ASCII values

Encryption of text characters using ASCII values

Akanksha Mathur Gujarat University Ahmedabad, India akanmamthur@gmail.com

Arshi Riyaz

Department of Computer Science and Engineering JIET Universe, Jodhpur, India arshiriyaz@gmail.com

Jyoti Vyas

Department of Computer Science and Engineering JIET Universe, Jodhpur, India jyotivyas@jietjodhpur.com

AbstractThis paper is demonstrating the encryption and decryption of text characters using their ASCII values. This is a kind of symmetric Encryption algorithm in which same key is used for both encryption and decryption purpose.

KeywordsASCII, encryption, Decryption, ciphertext, plaintext, cryptographic algorithm

1. A cryptographic algorithm is a mathematical functions and unchanging set of steps to perform encryption and decryption of the original data. These algorithms work in combination with a secret key which can be a combination of alphabets, numbers, words or phrases. For the purpose of encryption, the algorithm combines the original data or the text to be encoded (plaintext which is input to the encryption process) with the secret key supplied for the encryption. This combination will yield a ciphertext (which is our desired code or we can say output). Similarly, for the purpose of decryption, the algorithm combines the encrypted data or ciphertext with may or may not be the same secret key and this combination will yield again the same plaintext. If there is any modification takes place in any of the secret key or the plaintext, the algorithm will yield a different result than before. The main objective of every cryptographic algorithm is to make it as difficult as possible to decrypt the generated ciphertext without using the key. If a really good cryptographic algorithm is used, then there is no technique significantly better than methodically trying every possible combination of key.

2. 1. Introduction

      This algorithm is used to encrypt data by using ASCII values of the data to be encrypted. The secret key used will be modified to another string and that string is used as a key to encrypt or decrypt the data.[3] So, it can be said that it is a

      kind of symmetric encryption algorithm. In symmetric encryption algorithm, only one key is used for both encryption and decryption process. The key is transmitted to both the sender and receiver before the process of encryption and decryption. So, the secret key plays an important role and its strength depends on the length of key (in bits). The longer the length of key is, it is harder to break it and shorter the length of key is it is even easier to break it. [1] Thus it violates the security purpose of encryption. Similarly .it uses same key for encryption and decryption but by slightly modifying it.

      The main limitation of this algorithm is that it will operates when the length of input and the length of key are same. That is, if the length of input is 3 then the length of key must be 3 neither less or nor more than 3.

   2. Algorithm for encryprion process

      1. Start

      2. Input the string (can include numbers, alphabets and special symbols) from the user. This string is known as the plain text to be encrypted.

      3. Get the ASCII values of each character of plain text and store them in an array asciicontent.

      4. Find out the minimum value min from the array asciicontent. This min value is used further in the algorithm.

      5. For I = 1 to n where n is the length of the input of the plain text

         modcontent[I] = asciicontent[I] % min

         If the value of mod content is greater than 16, then again perform modcontent %16, and record the places where changes occur or record the positions in record array where the value of mod content is greater than 16.

      6. Input the string (can include numbers, alphabets and special symbols) from the user. This string is the key which is used to encrypt the plain text.\

      7. Get the ASCII values of each character of key and store them in an array asciikey.

      8. For I = 1 to n where n is the length of the input of the key modkey[I] = asciikey[I] % min

      9. Take the binary values of each value of modkey.

      10. Perform the right circular shifts of binary values n times (where n is the length of input i.e. plain text) and save them in binary array.

      11. Add min value to each ASCII value of each character of encrypt key after shifting.

          Encryptkey[I]=ASCII (Binary[I]) + min Encryptkey is the final key which is used to encrypt the plain text.

      12. To encrypt the original data (input) or plaintext to generate ciphertext, add each mod content value to the ASCII values of final encrypt key.

      13. Ciphertext[I]=ASCII(Excryptley[I])+modcontent[I Convert the ASCII values into their corresponding characters to get the cipher text.

   3. Algorithm for decryption purpose

   1. Start

   2. Get the ASCII values of each character of cipher text in

      asciicipher.

   3. Find out the minimum from ASCII values of each character of cipher text.

   4. Subtract ASCII values of final encrypt key from asciicipher

      Difference[I]=asciicipher[I]-ASCII(Encryptkey[I]) Add 16 to the stored positions from record array where the modcontent value is greater than 16.

   5. Add minimum to each value of difference to generate plaintext.

3. Here, representing some of the examples of encryption and decryption process of varying length of input (or key) say 2, 3, 4, 5.

   1. Example 1: Input Length:- 2

      Let Plain text is: – am Key is: – ab

      TABLE 1. EXAMPLE 1

      Encryptkey (After adding min)	101	97
      Encryptkey	e	a
      ASCII(Excryptley)+modcontent	101	109
      Ciphertext	e	m
      DECRYPTION
      Cipher	e	m
      ASCIICipher	101	109
      minimum=101
      asciifinalencryptkey	101	97
      difference	0	12
      asciiplain	97	109
      plaintext`	a	m

      Execution time: 320ms.

   2. Example 2: Input Length: – 3

      Let Plain text=bcf Key=cbc

      ENCRYPTION
      Input (Plain Text)	b	c	f
      asciicontent	98	99	102
      min=98
      modcontent	0	1	4
      Key	c	b	c
      asciikey	99	98	99
      modkey	1	0	1
      binary	0001	0000	0001
      Right Circular Shifts (3 times)
      Shift 1	1000	1000	0000
      Shift2	0100	0100	0000
      Shift 3	0010	0010	0000
      Encryptkey	2	2	0
      Encryptkey (After adding min)	100	100	98
      Encryptkey	d	d	b
      ASCII(Excryptley)+modcontent	100	101	102
      Ciphertext	d	e	f
      DECRYPTION

      TABLE 2. EXAMPLE 2.

      ENCRYPTION
      Input (Plain Text)	a	m
      asciicontent	97	109
      min=97
      modcontent	0	12
      Key	a	b
      asciikey	97	98
      modkey	0	1
      binary	0000	0001
      Right Circular Shifts (2 times)
      Shift 1	1000	0000
      Shift 2	0100	0000
      Encryptkey	4	0

      Cipher	d	e		f	Difference	13	4	7	0
      ASCIICipher	100	101	1	02	Asciiplain	110	101	104	97
      minimum=100
      					plaintext`	n	e	h	a
      asciifinalencryptkey	100	100
      			98.		imated Time: 3679 ms. Example 4:Inuput Length: -5 plaintext= pacgl Key=abcde
      difference	0	1	4Est
      asciiplain	98	99	10D2 .
      plaintext`	b	c	fLet

      Execution Time: 2098ms.

   3. Example 3: Input Length: – 4

   Let Plain Text= neha Key= abcd

   TABLE 3. EXAMPLE 3

   ENCRYPTION
   Input (Plain Text)	p	a	c	g	l
   asciicontent	112	97	99	103	108
   min=97
   modcontent	15	0	2	6	11
   Key	a	b	c	d	e
   asciikey	97	98	99	100	101
   modkey	0	1	2	3	4
   binary	0000	0001	0010	0011	0100
   Right Circular Shifts (5 times)
   Shift 1	0000	0000	1001	0001	1010
   Shift 2	0000	0000	0100	1000	1101
   Shift 3	1000	0000	0010	0100	0110
   Shift 4	0100	0000	0001	0010	0011
   Shift 5	1010	0000	0000	1001	0001
   Encryptkey	10	0	0	9	1
   Encryptkey (After adding min)	107	97	97	106	98
   Encryptkey	k	a	a	j	b
   ASCII(Excryptley)+ modcontent	122	97	99	112	109
   Ciphertext	z	a	c	p	m
   DECRYPTION
   Cipher	z	a	c	p	m
   ASCIICipher	122	97	99	112	109
   minimum=97
   Asciifinal encryptkey	107	97	97	106	98
   difference	15	0	2	6	11
   asciiplain	112	97	99	103	108
   plaintext`	p	a	c	g	l

   TABLE 4. EXAMPLE 4

   ENCRYPTION
   Input (Plain Text)	n	e	h	a
   asciicontent	110	101	104	97
   min=97
   Modcontent	13	4	7	0
   Key	a	b	c	d
   Asciikey	97	98	99	100
   Modkey	0	1	2	3
   Binary	0000	0001	0010	0011
   Right Circular Shifts (4 times)
   Shift 1	1000	0000	1001	0001
   Shift 2	1100	0000	0100	1000
   Shift 3	0110	0000	0010	0100
   Shift 4	0011	0000	0001	0010
   Encryptkey	3	0	1	2
   Encryptkey (After adding min)	100	97	98	99
   Encryptkey	d	a	b	c
   ASCII(Excryptley)+ modcontent	113	<>101	105	99
   Ciphertext	q	e	i	c
   DECRYPTION
   Cipher	q	e	i		c
   ASCIICipher	113	101	105		99
   minimum=99
   Asciifinalencryptkey	100	97	98		99

   Execution Time:: 3780ms.

4. The proposed algorithm has the following limitations:-

   1. More Execution time

   2. Key Length and length of plain text must be same.[3]

   3. If it is applied on any file then the length of key is equal to the length of file which is not considered as good

5. In the future wok related to proposed algorithm, the limitations of proposed algorithm are overcome by

   1. Encrypting and decrypting data with may or may not be same key length size in comparison with input size.

   2. Appling on files of different length

   3. Applied on images

1. Gurjeevan Singh, Ashwani Kumar Singla, K.S. Sandha, Throughput Analysis of Various Encryption Algorithms, International Journal of Computer Science and Technology, Vol. 2, Issue 3, Septemver 2011.

2. Diaa Salama Abd Elminaam, Hatem Mohamed Abdual Kader, and Mohiy Mohamed Hadhoud, Evaluating the Performance of Symmetric Encryption Algorithms, International Journal of Network Security, Vol.10, No.3, PP.216222, May 2010.