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Playfair Cipher

In this scheme, pairs of letters are encrypted, instead of single letters as in the case of simple substitution cipher. In playfair cipher, initially a key table is created. The key table is a 5×5 grid of alphabets that acts as the key for encrypting the plaintext. Each of the 25 alphabets must be unique… Continue reading Playfair Cipher

Simple Substitution Cipher

It is an improvement to the Caesar Cipher. Instead of shifting the alphabets by some number, this scheme uses some permutation of the letters in alphabet. For example, A.B…..Y.Z and Z.Y……B.A are two obvious permutation of all the letters in alphabet. Permutation is nothing but a jumbled up set of alphabets. With 26 letters in… Continue reading Simple Substitution Cipher

Traditional Ciphers

In the second chapter, we discussed the fundamentals of modern cryptography. We equated cryptography with a toolkit where various cryptographic techniques are considered as the basic tools. One of these tools is the Symmetric Key Encryption where the key used for encryption and decryption is the same. In this chapter, we discuss this technique further… Continue reading Traditional Ciphers

Cryptographic Attacks

The basic intention of an attacker is to break a cryptosystem and to find the plaintext from the ciphertext. To obtain the plaintext, the attacker only needs to find out the secret decryption key, as the algorithm is already in public domain. Hence, he applies maximum effort towards finding out the secret key used in… Continue reading Cryptographic Attacks

Details of the Encryption Scheme

The design of a cryptosystem is based on the following two cryptography algorithms − In case of proprietary algorithms, security is ensured through obscurity. Private algorithms may not be the strongest algorithms as they are developed in-house and may not be extensively investigated for weakness. Secondly, they allow communication among closed group only. Hence they… Continue reading Details of the Encryption Scheme

Active Attacks

An active attack involves changing the information in some way by conducting some process on the information. For example, Cryptography provides many tools and techniques for implementing cryptosystems capable of preventing most of the attacks described above. Assumptions of Attacker Let us see the prevailing environment around cryptosystems followed by the types of attacks employed… Continue reading Active Attacks

Attacks On Cryptosystems

In the present era, not only business but almost all the aspects of human life are driven by information. Hence, it has become imperative to protect useful information from malicious activities such as attacks. Let us consider the types of attacks to which information is typically subjected to. Attacks are typically categorized based on the… Continue reading Attacks On Cryptosystems

Challenge of Symmetric Key Cryptosystem

There are two restrictive challenges of employing symmetric key cryptography. These two challenges are highly restraining for modern day communication. Today, people need to exchange information with non-familiar and non-trusted parties. For example, a communication between online seller and customer. These limitations of symmetric key encryption gave rise to asymmetric key encryption schemes. Asymmetric Key… Continue reading Challenge of Symmetric Key Cryptosystem

Components of a Cryptosystem

The various components of a basic cryptosystem are as follows − For a given cryptosystem, a collection of all possible decryption keys is called a key space. An interceptor (an attacker) is an unauthorized entity who attempts to determine the plaintext. He can see the ciphertext and may know the decryption algorithm. He, however, must never know the… Continue reading Components of a Cryptosystem