The basic scheme of a block cipher is depicted as follows − A block cipher takes a block of plaintext bits and generates a block of ciphertext bits, generally of same size. The size of block is fixed in the given scheme. The choice of block size does not directly affect to the strength of… Continue reading Block Cipher
Month: November 2022
Modern Symmetric Key Encryption
Digital data is represented in strings of binary digits (bits) unlike alphabets. Modern cryptosystems need to process this binary strings to convert in to another binary string. Based on how these binary strings are processed, a symmetric encryption schemes can be classified in to − Block Ciphers In this scheme, the plain binary text is… Continue reading Modern Symmetric Key Encryption
Security Value
Vigenere Cipher was designed by tweaking the standard Caesar cipher to reduce the effectiveness of cryptanalysis on the ciphertext and make a cryptosystem more robust. It is significantly more secure than a regular Caesar Cipher. In the history, it was regularly used for protecting sensitive political and military information. It was referred to as the unbreakable cipher due… Continue reading Security Value
Security Value
It is also a substitution cipher and is difficult to break compared to the simple substitution cipher. As in case of substitution cipher, cryptanalysis is possible on the Playfair cipher as well, however it would be against 625 possible pairs of letters (25×25 alphabets) instead of 26 different possible alphabets. The Playfair cipher was used… Continue reading Security Value
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