### Arithmetic Exprerssion

ARITHMETIC EXPRESSION It is a combination of variables, constants and operators arranged as per the syntax of the language. C can handle any complex mathematical expressions EXAMPLE: A LGEBRIC EXPRESSIONS C EXPRESSION ax b –c a*b-c (m+n)(x+y) (m+n)*(x+y) (ab/c) a*b/c 3*x*x 2*x+1 (x/y)+c x/y+c EVALUATION OF EXPRESSIONS Expressions are evaluated using an assignment statement of […]

### Conventional Encryption

CONVENTIONAL ENCRYPTION Let us illustrate the principles of modern conventional encryption . For this purpose, we focus of the most widely used conventional encryption algorithms: The Data Encryption Standard (DES). Although numerous conventional encryption algorithms have been developed since the introduction of DES, it remains the most important such algorithms. Further, a detailed study of DES […]

### S-DES key Generation

S – DES KEY GENERATION S – DES depends on the use of 10-bit key shared between sender and receiver. From this key, two 8-bit sub keys are produced for use in particular stages of the encryption and decryption algorithm First and foremost we need to generate a key. With the help of this we […]

### Simplified DES

INTRODUCTION: Simplified DES is a secure encryption algorithm. It has similar properties and structure to DES with much smaller parameters. It was developed by Professor Edward Schaefer of Santa Clara University. PROCESS: The S-DES encryption algorithm takes an 8-bit block of plaintext and a 10-bit key as input and produces an 8-bit block of ciphertext […]

### Rotor Machine Working Model

Rotor Machine: It was invented by Edward Hebern. Rotor Machines is as true of substitution chipers as it is of transpostion chipers. The most important applications of the principle of multiple stages of encryption was a class of systems known as rotor machines. Polyalphabetic substitution: Consider a machine with a single cylinder After each input […]

### Principles of Rotor machines

Definition: Rotor machines combined several disks into a single device which had a much larger number of monoalphabetic ciphers, enough to defeat statistical analysis in principle Basic principle of the rotor machine: The machine consists of a set of independently rotating cylinders through which electrical pulses can flow. Each cylinder has 26 input pins and […]

### Transposition Terchniques

Introduction: From the encryption algorithm point of view, there are two main techniques we used to implement in the secret key cryptography (symmetric cipher) system: Substitution cipher and Transposition cipher. Substitution ciphers replace bits, characters, or blocks of characters with substitution. Transposition ciphers rearrange bits or characters in the data. We […]

### Polyalphabetic ciphers

POLYALPHABETIC CIPHERS Another way to improve on the simple monoalphabetic technique is to use different monoalphabetic substitutions as one proceeds through the plaintext message. The general name for this approach is polyalphabetic cipher. All these techniques have the following features in common. A set of related monoalphabetic substitution rules is used. A key determines which […]

### HILL CIPHER

INTRODUCTION: Another interesting multi letter cipher is the Hill cipher, developed by the mathematician Lester Hill in 1929. STRUCTURE: The encryption algorithm takes m successive plain text letters and substitutes for them m cipher letters. The substitution is determined by m linear equations in which each character is assigned a numerical value(a=0,b=1,…z=25). For m=3, the […]