This document provides an overview of traditional symmetric-key ciphers. It begins by defining symmetric-key ciphers and their basic components. It then outlines the chapter's objectives and topics: substitution ciphers, transposition ciphers, stream ciphers, and block ciphers. The document proceeds to describe various traditional ciphers that fall under each of these categories, including monoalphabetic and polyalphabetic substitution ciphers, rail fence transposition cipher, and the Enigma machine cipher. It provides examples of encrypting and decrypting messages with these different ciphers.
- Traditional symmetric key ciphers can be categorized as either substitution ciphers, which replace symbols, or transposition ciphers, which change the location of symbols.
- For substitution ciphers, the document describes various monoalphabetic ciphers (such as the Caesar cipher) and polyalphabetic ciphers (such as the Vigenere cipher and Hill cipher).
- For transposition ciphers, it discusses both keyless transposition techniques like the rail fence cipher as well as keyed transposition ciphers that permute symbols within blocks defined by a key.
This document discusses traditional symmetric key ciphers. It describes how symmetric key ciphers use the same key to encrypt and decrypt data. The document categorizes traditional symmetric key ciphers into substitution ciphers like monoalphabetic and polyalphabetic ciphers, and transposition ciphers like keyed and keyless transposition ciphers. It also provides examples of how different symmetric key ciphers like the Caesar cipher, shift cipher, additive cipher, and multiplicative cipher operate.
This document discusses transposition ciphers, which is a method of encryption where the positions of plaintext units are shifted according to a regular system to produce the ciphertext. The order of units is changed by using a bijective function on the characters' positions to encrypt and an inverse function to decrypt. Some common transposition ciphers mentioned include the rail fence cipher, route cipher, columnar transposition, double transposition, and Myszkowski transposition. Cryptanalysis techniques for transposition ciphers involve analyzing letter frequencies and determining the number of columns. One-time pads are also briefly discussed, which use random bit strings for encryption but have limitations such as requiring the key to be securely transported.
1. The document discusses network security and provides details about stream ciphers and block ciphers. It explains how each type of cipher works and provides examples of each.
2. Details are given about the Feistel cipher structure and how it provides diffusion and confusion through repeated rounds. The Data Encryption Standard (DES) algorithm is described as a prominent example of a Feistel cipher.
3. Principles of block cipher design are outlined, emphasizing the importance of number of rounds, design of the round function F, and the key schedule algorithm in providing security.
Cryptography is the practice of securing communication and information by converting plaintext into ciphertext. The document provides an introduction to cryptography including its history from ancient times to the present. It discusses terminology like plaintext, encryption, ciphertext, decryption, and keys. Symmetric key cryptography uses a single key for encryption and decryption while asymmetric key cryptography uses two different keys. Examples of symmetric methods are DES, 3DES, AES, and RC4, while RSA is a common asymmetric method. Applications of cryptography include ATMs, email passwords, e-payments, e-commerce, electronic voting, defense services, securing data, and access control.
This presentation contains the contents pertaining to the undergraduate course on Cryptography and Network Security (UITC203) at Sri Ramakrishna Institute of Technology. This covers the Data Encryption Standard and its variants.
This document presents an overview of cryptography including its definition, history, basic terms, classifications, techniques, advantages, disadvantages, and applications. Cryptography is defined as the art and science of achieving security by encoding messages. The earliest evidence of cryptography dates back 4000 years to ancient Egypt. Techniques covered include symmetric and asymmetric encryption, transposition ciphers, substitution ciphers, block ciphers, stream ciphers, hashing, and steganography. Advantages of cryptography include confidentiality, authentication, data integrity, and non-repudiation, while disadvantages include reduced accessibility and inability to ensure high availability. Cryptography has applications in defense, e-commerce, business transactions, internet payments, user identification, and data security.
- Traditional symmetric key ciphers can be categorized as either substitution ciphers, which replace symbols, or transposition ciphers, which change the location of symbols.
- For substitution ciphers, the document describes various monoalphabetic ciphers (such as the Caesar cipher) and polyalphabetic ciphers (such as the Vigenere cipher and Hill cipher).
- For transposition ciphers, it discusses both keyless transposition techniques like the rail fence cipher as well as keyed transposition ciphers that permute symbols within blocks defined by a key.
This document discusses traditional symmetric key ciphers. It describes how symmetric key ciphers use the same key to encrypt and decrypt data. The document categorizes traditional symmetric key ciphers into substitution ciphers like monoalphabetic and polyalphabetic ciphers, and transposition ciphers like keyed and keyless transposition ciphers. It also provides examples of how different symmetric key ciphers like the Caesar cipher, shift cipher, additive cipher, and multiplicative cipher operate.
This document discusses transposition ciphers, which is a method of encryption where the positions of plaintext units are shifted according to a regular system to produce the ciphertext. The order of units is changed by using a bijective function on the characters' positions to encrypt and an inverse function to decrypt. Some common transposition ciphers mentioned include the rail fence cipher, route cipher, columnar transposition, double transposition, and Myszkowski transposition. Cryptanalysis techniques for transposition ciphers involve analyzing letter frequencies and determining the number of columns. One-time pads are also briefly discussed, which use random bit strings for encryption but have limitations such as requiring the key to be securely transported.
1. The document discusses network security and provides details about stream ciphers and block ciphers. It explains how each type of cipher works and provides examples of each.
2. Details are given about the Feistel cipher structure and how it provides diffusion and confusion through repeated rounds. The Data Encryption Standard (DES) algorithm is described as a prominent example of a Feistel cipher.
3. Principles of block cipher design are outlined, emphasizing the importance of number of rounds, design of the round function F, and the key schedule algorithm in providing security.
Cryptography is the practice of securing communication and information by converting plaintext into ciphertext. The document provides an introduction to cryptography including its history from ancient times to the present. It discusses terminology like plaintext, encryption, ciphertext, decryption, and keys. Symmetric key cryptography uses a single key for encryption and decryption while asymmetric key cryptography uses two different keys. Examples of symmetric methods are DES, 3DES, AES, and RC4, while RSA is a common asymmetric method. Applications of cryptography include ATMs, email passwords, e-payments, e-commerce, electronic voting, defense services, securing data, and access control.
This presentation contains the contents pertaining to the undergraduate course on Cryptography and Network Security (UITC203) at Sri Ramakrishna Institute of Technology. This covers the Data Encryption Standard and its variants.
This document presents an overview of cryptography including its definition, history, basic terms, classifications, techniques, advantages, disadvantages, and applications. Cryptography is defined as the art and science of achieving security by encoding messages. The earliest evidence of cryptography dates back 4000 years to ancient Egypt. Techniques covered include symmetric and asymmetric encryption, transposition ciphers, substitution ciphers, block ciphers, stream ciphers, hashing, and steganography. Advantages of cryptography include confidentiality, authentication, data integrity, and non-repudiation, while disadvantages include reduced accessibility and inability to ensure high availability. Cryptography has applications in defense, e-commerce, business transactions, internet payments, user identification, and data security.
This document discusses steganography and image steganography techniques. It defines steganography as hiding information within other information to avoid detection. Image steganography is described as hiding data in digital images using techniques like least significant bit encoding. The document outlines the LSB algorithm, which replaces the least significant bits of image pixel values with bits of the hidden message. Examples are given to illustrate how short messages can be concealed in an image using this method.
The document discusses classical encryption techniques such as substitution ciphers like the Caesar cipher and monoalphabetic cipher, transposition ciphers like the rail fence cipher and row transposition cipher, and polyalphabetic ciphers like the Vigenere cipher. It introduces basic concepts and terminology in cryptography such as plaintext, ciphertext, encryption, decryption, and secret keys. The goals are to introduce basic concepts and terminology of encryption and to prepare for studying modern cryptography.
Symmetric Key Encryption Algorithms can be categorized as stream ciphers or block ciphers. Block ciphers like the Data Encryption Standard (DES) operate on fixed-length blocks of bits, while stream ciphers process messages bit-by-bit. DES is an example of a block cipher that encrypts 64-bit blocks using a 56-bit key. International Data Encryption Algorithm (IDEA) is another block cipher that uses a 128-bit key and 64-bit blocks, employing addition and multiplication instead of XOR like DES. IDEA consists of 8 encryption rounds followed by an output transformation to generate the ciphertext from the plaintext and key.
substitution and transposition techniques_ppt.pptxGauriBornare1
The document presents a web-based application for encrypting messages using substitution and transposition techniques like the Caesar cipher, Playfair cipher, rail fence transposition, and simple columnar transposition. The application aims to securely transmit sensitive information over the internet by making encryption accessible without specialized cryptography knowledge. It explains each encryption technique with examples, and concludes that combining multiple ciphers in the system ensures confidentiality and makes encrypted messages difficult to crack without the key.
Caesar Cipher , Substitution Cipher, PlayFair and Vigenere CipherMona Rajput
The document provides information on various historical cryptosystems and ciphers, beginning with a brief overview of symmetric and asymmetric key encryption. It then discusses several manual ciphers such as the Caesar cipher, simple substitution cipher, Playfair cipher, and Vigenere cipher. The Caesar cipher performs monoalphabetic substitution by shifting letters of the alphabet. The simple substitution cipher and Playfair cipher improve security by using permutation or paired letter substitution instead of just shifting. The Vigenere cipher further enhances security by applying multiple Caesar shifts using a keyword. The document also covers the one-time pad cipher and its information theoretic security if the pad is truly random and never reused.
Public-key cryptography uses two keys: a public key that can encrypt messages and verify signatures, and a private key that can decrypt messages and create signatures. The RSA algorithm is widely used for public-key cryptography. It works by using large prime numbers to generate the public and private keys, such that it is easy to encrypt with the public key but computationally infeasible to derive the private key and decrypt without knowing the prime numbers. The security of RSA relies on the difficulty of factoring the product of the large prime numbers. Timing attacks aim to break RSA security by analyzing variations in computation times, but countermeasures can prevent leaks of private information.
In cryptography, a block cipher is a deterministic algorithm operating on ... Systems as a means to effectively improve security by combining simple operations such as .... Finally, the cipher should be easily cryptanalyzable, such that it can be ...
The document discusses various cryptographic techniques for encrypting messages. It begins by defining key terminology used in cryptography. It then explains the basic principles of conventional encryption, which uses a secret key shared between the sender and receiver. The document outlines different types of cryptanalytic attacks and describes brute force search attacks. It classifies cryptographic techniques based on the type of operations used, number of keys, and how plaintext is processed. Finally, it provides examples of specific symmetric encryption techniques like the Caesar cipher, Playfair cipher, Vigenère cipher, one-time pad cipher, and transposition ciphers like the rail fence cipher and row transposition cipher.
Symmetric and asymmetric key cryptographyMONIRUL ISLAM
The document discusses symmetric and asymmetric key cryptography. It begins with an introduction to cryptography and its objectives of confidentiality, integrity, authentication and non-repudiation. It then explains the differences between symmetric and asymmetric cryptosystems. Symmetric cryptosystems involve a shared key between sender and receiver, while asymmetric cryptosystems use public and private key pairs. Examples of traditional symmetric ciphers like simple substitution and transposition ciphers are provided. The document also outlines the RSA algorithm as an example of asymmetric cryptography and discusses some limitations of both symmetric and asymmetric approaches.
Introduction to cryptography and types of ciphersAswathi Nair
Cryptography is a method of storing and transmitting data in a particular form so that only those for whom it is intended can read and process it.So these slides give you an introduction to cryptography and types of ciphers.
The document provides an overview of cipher techniques including:
- Classical techniques like transposition ciphers, substitution ciphers including the Caesar and Playfair ciphers, and polyalphabetic ciphers like the Vigenere cipher.
- Modern techniques like stream ciphers which encrypt bits one at a time using a pseudorandom keystream, and block ciphers which encrypt blocks of text.
- It also discusses cryptanalysis techniques for analyzing ciphers and discusses how to build more secure systems using techniques like the one-time pad or combining multiple ciphers.
This document provides an overview of cryptography. It defines cryptography as the science of secret writing and discusses its use in applications like ATM cards and passwords. It describes the basic components of cryptography including plaintext, ciphertext, ciphers, keys, and algorithms. It differentiates between symmetric and asymmetric key cryptography. It provides examples of traditional and modern ciphers, including DES, AES, and RSA algorithms. In conclusion, it states that cryptography techniques help maintain data security, privacy, and integrity.
The document discusses cryptography concepts including encryption, decryption, symmetric and asymmetric encryption techniques, cryptanalysis methods like brute force attacks, and the importance of secret keys. Symmetric encryption uses a shared secret key by both sender and receiver, while asymmetric encryption uses different public/private keys. Cryptanalysis aims to discover plaintext or keys by techniques like brute force trials or exploiting algorithm weaknesses. Longer cryptographic keys increase the difficulty of brute force attacks breaking the encryption.
Asymmetric key cryptography uses two keys - a public key that can be shared publicly and a private key that is kept secret. This allows two parties who have never shared secrets before, like Alice and Bob, to communicate securely by encrypting messages with each other's public keys. Common asymmetric algorithms discussed are RSA, which uses prime number factorization, and ECC, which is based on elliptic curve discrete logarithms. A public key infrastructure (PKI) with certificate authorities (CAs) is required to authenticate users and manage public keys.
This document summarizes a chapter about the Data Encryption Standard (DES). It provides an overview of DES, describing it as a symmetric-key block cipher developed by IBM and adopted by the National Institute of Standards and Technology. The chapter then goes into details about the structure and design of DES, including its use of an initial and final permutation, 16 rounds of encryption using subkey values, and weaknesses like its short key length. It also discusses analyses of DES security, noting brute force, differential cryptanalysis, and linear cryptanalysis as potential attack methods.
This document discusses the science of encryption through three main topics: the purpose and history of cryptography, modern cryptography techniques, and password security. It describes cryptography as the science of secure communications and its goals of authentication, privacy, integrity, and non-repudiation. The history of cryptography is divided into ancient uses and electro-mechanical machines of World War II. Modern techniques discussed are secret key cryptography, hash functions, and public key cryptography. It emphasizes the importance of strong, unique passwords for security.
The presentation covers the following:
Basic Terms
Cryptography
The General Goals of Cryptography
Common Types of Attacks
Substitution Ciphers
Transposition Cipher
Steganography- “Concealed Writing”
Symmetric Secret Key Encryption
Types of Symmetric Algorithms
Common Symmetric Algorithms
Asymmetric Secret Key Encryption
Common Asymmetric Algorithms
Public Key Cryptography
Hashing Techniques
Hashing Algorithms
Digital Signatures
Transport Layer Security
Public key infrastructure (PKI)
Here are the solutions to the questions:
Q1. Rail Fence Cipher for "Networking" using 2 lines:
Nkttn
eorwige
Ciphertext: Nkttnorwige
Q2. Single columnar transposition for "COMPUTERSCIENCE" using keyword "ORANGE":
C O M P U T
E R S C I E N
C E
Ciphertext: COEMNPUSTIERC
Q3. Single columnar transposition for "COMPUTERSCIENCE" using keyword "PINEAPPLE":
C O M P U T
E R S C I E N
C E
Ciphertext
This document provides an overview of traditional symmetric-key ciphers. It begins by defining symmetric-key ciphers and their basic components. It then outlines the chapter's objectives and topics, which include substitution and transposition ciphers as well as cryptanalysis techniques. The document proceeds to describe various substitution ciphers like monoalphabetic, polyalphabetic, additive, affine and Playfair ciphers. It also covers transposition ciphers, including keyless rail fence cipher and keyed block permutation ciphers. Examples are provided to illustrate encryption and decryption processes for different ciphers.
The document summarizes key concepts related to symmetric ciphers. It discusses traditional ciphers such as substitution ciphers (monoalphabetic and polyalphabetic) and transposition ciphers. It also introduces modern categories of stream ciphers and block ciphers. Specific traditional ciphers covered include the Caesar cipher, Vigenere cipher, Playfair cipher, Hill cipher, and the one-time pad. The document emphasizes that the security of symmetric ciphers relies on keeping the secret key private.
This document discusses steganography and image steganography techniques. It defines steganography as hiding information within other information to avoid detection. Image steganography is described as hiding data in digital images using techniques like least significant bit encoding. The document outlines the LSB algorithm, which replaces the least significant bits of image pixel values with bits of the hidden message. Examples are given to illustrate how short messages can be concealed in an image using this method.
The document discusses classical encryption techniques such as substitution ciphers like the Caesar cipher and monoalphabetic cipher, transposition ciphers like the rail fence cipher and row transposition cipher, and polyalphabetic ciphers like the Vigenere cipher. It introduces basic concepts and terminology in cryptography such as plaintext, ciphertext, encryption, decryption, and secret keys. The goals are to introduce basic concepts and terminology of encryption and to prepare for studying modern cryptography.
Symmetric Key Encryption Algorithms can be categorized as stream ciphers or block ciphers. Block ciphers like the Data Encryption Standard (DES) operate on fixed-length blocks of bits, while stream ciphers process messages bit-by-bit. DES is an example of a block cipher that encrypts 64-bit blocks using a 56-bit key. International Data Encryption Algorithm (IDEA) is another block cipher that uses a 128-bit key and 64-bit blocks, employing addition and multiplication instead of XOR like DES. IDEA consists of 8 encryption rounds followed by an output transformation to generate the ciphertext from the plaintext and key.
substitution and transposition techniques_ppt.pptxGauriBornare1
The document presents a web-based application for encrypting messages using substitution and transposition techniques like the Caesar cipher, Playfair cipher, rail fence transposition, and simple columnar transposition. The application aims to securely transmit sensitive information over the internet by making encryption accessible without specialized cryptography knowledge. It explains each encryption technique with examples, and concludes that combining multiple ciphers in the system ensures confidentiality and makes encrypted messages difficult to crack without the key.
Caesar Cipher , Substitution Cipher, PlayFair and Vigenere CipherMona Rajput
The document provides information on various historical cryptosystems and ciphers, beginning with a brief overview of symmetric and asymmetric key encryption. It then discusses several manual ciphers such as the Caesar cipher, simple substitution cipher, Playfair cipher, and Vigenere cipher. The Caesar cipher performs monoalphabetic substitution by shifting letters of the alphabet. The simple substitution cipher and Playfair cipher improve security by using permutation or paired letter substitution instead of just shifting. The Vigenere cipher further enhances security by applying multiple Caesar shifts using a keyword. The document also covers the one-time pad cipher and its information theoretic security if the pad is truly random and never reused.
Public-key cryptography uses two keys: a public key that can encrypt messages and verify signatures, and a private key that can decrypt messages and create signatures. The RSA algorithm is widely used for public-key cryptography. It works by using large prime numbers to generate the public and private keys, such that it is easy to encrypt with the public key but computationally infeasible to derive the private key and decrypt without knowing the prime numbers. The security of RSA relies on the difficulty of factoring the product of the large prime numbers. Timing attacks aim to break RSA security by analyzing variations in computation times, but countermeasures can prevent leaks of private information.
In cryptography, a block cipher is a deterministic algorithm operating on ... Systems as a means to effectively improve security by combining simple operations such as .... Finally, the cipher should be easily cryptanalyzable, such that it can be ...
The document discusses various cryptographic techniques for encrypting messages. It begins by defining key terminology used in cryptography. It then explains the basic principles of conventional encryption, which uses a secret key shared between the sender and receiver. The document outlines different types of cryptanalytic attacks and describes brute force search attacks. It classifies cryptographic techniques based on the type of operations used, number of keys, and how plaintext is processed. Finally, it provides examples of specific symmetric encryption techniques like the Caesar cipher, Playfair cipher, Vigenère cipher, one-time pad cipher, and transposition ciphers like the rail fence cipher and row transposition cipher.
Symmetric and asymmetric key cryptographyMONIRUL ISLAM
The document discusses symmetric and asymmetric key cryptography. It begins with an introduction to cryptography and its objectives of confidentiality, integrity, authentication and non-repudiation. It then explains the differences between symmetric and asymmetric cryptosystems. Symmetric cryptosystems involve a shared key between sender and receiver, while asymmetric cryptosystems use public and private key pairs. Examples of traditional symmetric ciphers like simple substitution and transposition ciphers are provided. The document also outlines the RSA algorithm as an example of asymmetric cryptography and discusses some limitations of both symmetric and asymmetric approaches.
Introduction to cryptography and types of ciphersAswathi Nair
Cryptography is a method of storing and transmitting data in a particular form so that only those for whom it is intended can read and process it.So these slides give you an introduction to cryptography and types of ciphers.
The document provides an overview of cipher techniques including:
- Classical techniques like transposition ciphers, substitution ciphers including the Caesar and Playfair ciphers, and polyalphabetic ciphers like the Vigenere cipher.
- Modern techniques like stream ciphers which encrypt bits one at a time using a pseudorandom keystream, and block ciphers which encrypt blocks of text.
- It also discusses cryptanalysis techniques for analyzing ciphers and discusses how to build more secure systems using techniques like the one-time pad or combining multiple ciphers.
This document provides an overview of cryptography. It defines cryptography as the science of secret writing and discusses its use in applications like ATM cards and passwords. It describes the basic components of cryptography including plaintext, ciphertext, ciphers, keys, and algorithms. It differentiates between symmetric and asymmetric key cryptography. It provides examples of traditional and modern ciphers, including DES, AES, and RSA algorithms. In conclusion, it states that cryptography techniques help maintain data security, privacy, and integrity.
The document discusses cryptography concepts including encryption, decryption, symmetric and asymmetric encryption techniques, cryptanalysis methods like brute force attacks, and the importance of secret keys. Symmetric encryption uses a shared secret key by both sender and receiver, while asymmetric encryption uses different public/private keys. Cryptanalysis aims to discover plaintext or keys by techniques like brute force trials or exploiting algorithm weaknesses. Longer cryptographic keys increase the difficulty of brute force attacks breaking the encryption.
Asymmetric key cryptography uses two keys - a public key that can be shared publicly and a private key that is kept secret. This allows two parties who have never shared secrets before, like Alice and Bob, to communicate securely by encrypting messages with each other's public keys. Common asymmetric algorithms discussed are RSA, which uses prime number factorization, and ECC, which is based on elliptic curve discrete logarithms. A public key infrastructure (PKI) with certificate authorities (CAs) is required to authenticate users and manage public keys.
This document summarizes a chapter about the Data Encryption Standard (DES). It provides an overview of DES, describing it as a symmetric-key block cipher developed by IBM and adopted by the National Institute of Standards and Technology. The chapter then goes into details about the structure and design of DES, including its use of an initial and final permutation, 16 rounds of encryption using subkey values, and weaknesses like its short key length. It also discusses analyses of DES security, noting brute force, differential cryptanalysis, and linear cryptanalysis as potential attack methods.
This document discusses the science of encryption through three main topics: the purpose and history of cryptography, modern cryptography techniques, and password security. It describes cryptography as the science of secure communications and its goals of authentication, privacy, integrity, and non-repudiation. The history of cryptography is divided into ancient uses and electro-mechanical machines of World War II. Modern techniques discussed are secret key cryptography, hash functions, and public key cryptography. It emphasizes the importance of strong, unique passwords for security.
The presentation covers the following:
Basic Terms
Cryptography
The General Goals of Cryptography
Common Types of Attacks
Substitution Ciphers
Transposition Cipher
Steganography- “Concealed Writing”
Symmetric Secret Key Encryption
Types of Symmetric Algorithms
Common Symmetric Algorithms
Asymmetric Secret Key Encryption
Common Asymmetric Algorithms
Public Key Cryptography
Hashing Techniques
Hashing Algorithms
Digital Signatures
Transport Layer Security
Public key infrastructure (PKI)
Here are the solutions to the questions:
Q1. Rail Fence Cipher for "Networking" using 2 lines:
Nkttn
eorwige
Ciphertext: Nkttnorwige
Q2. Single columnar transposition for "COMPUTERSCIENCE" using keyword "ORANGE":
C O M P U T
E R S C I E N
C E
Ciphertext: COEMNPUSTIERC
Q3. Single columnar transposition for "COMPUTERSCIENCE" using keyword "PINEAPPLE":
C O M P U T
E R S C I E N
C E
Ciphertext
This document provides an overview of traditional symmetric-key ciphers. It begins by defining symmetric-key ciphers and their basic components. It then outlines the chapter's objectives and topics, which include substitution and transposition ciphers as well as cryptanalysis techniques. The document proceeds to describe various substitution ciphers like monoalphabetic, polyalphabetic, additive, affine and Playfair ciphers. It also covers transposition ciphers, including keyless rail fence cipher and keyed block permutation ciphers. Examples are provided to illustrate encryption and decryption processes for different ciphers.
The document summarizes key concepts related to symmetric ciphers. It discusses traditional ciphers such as substitution ciphers (monoalphabetic and polyalphabetic) and transposition ciphers. It also introduces modern categories of stream ciphers and block ciphers. Specific traditional ciphers covered include the Caesar cipher, Vigenere cipher, Playfair cipher, Hill cipher, and the one-time pad. The document emphasizes that the security of symmetric ciphers relies on keeping the secret key private.
This document discusses various topics in network security including cryptography, symmetric and asymmetric encryption algorithms, digital signatures, and firewalls. It provides detailed explanations and examples of symmetric key algorithms like monoalphabetic and polyalphabetic substitution ciphers, transpositional ciphers, and block ciphers like DES. It also covers asymmetric key algorithms like RSA and their use for encryption and digital signatures. Finally, it describes packet filter and proxy based firewalls and how they can be used to control network access.
Network security relies heavily on cryptography, which transforms messages to make them secure. There are two main categories of cryptography: symmetric-key cryptography where the same key is used to encrypt and decrypt, and asymmetric-key cryptography where different keys are used for encryption and decryption. Traditional symmetric-key ciphers include substitution ciphers that replace symbols and transposition ciphers that rearrange symbols. Modern symmetric-key ciphers operate on bits and are more complex.
This document discusses different techniques used in cryptography. It describes symmetric and asymmetric key cryptography. Symmetric cryptography uses a single secret key for encryption and decryption, while asymmetric cryptography uses public and private key pairs. The document also explains the Caesar cipher, Playfair cipher, polyalphabetic cipher, and transposition ciphers like the rail fence technique. It provides examples to illustrate how each technique works and encrypts messages.
The document provides an introduction to cryptography including definitions of terms and topics covered. It discusses symmetric-key cryptography and algorithms like substitution ciphers, transposition ciphers, DES, AES and their modes of operation. It also covers asymmetric-key cryptography including RSA and Diffie-Hellman key exchange with examples of encrypting and decrypting messages.
The document provides an introduction to cryptography including definitions of terms and topics covered. It discusses symmetric-key cryptography and algorithms like substitution ciphers, transposition ciphers, DES, AES and their modes of operation. It also covers asymmetric-key cryptography including RSA and Diffie-Hellman key exchange with examples of encrypting and decrypting messages.
This document summarizes the key aspects of encryption and decryption processes. It describes how plaintext is input into an encryption algorithm along with a secret key to produce ciphertext. The same encryption algorithm run in reverse along with the secret key is used to decrypt the ciphertext back into the original plaintext. Different encryption algorithms like Caesar cipher, substitution cipher, Hill cipher are discussed which use techniques like letter substitution, rearrangement and matrix multiplication to encrypt plaintext.
The document provides an overview of cryptography concepts including encryption, decryption, symmetric cryptosystems, block ciphers, substitution ciphers, the one-time pad, and algorithms such as DES, Triple DES, AES, and others. Key points covered include Kerckhoffs's principle of keeping algorithms public and keys private, how symmetric encryption works between two parties with a shared key, methods of encrypting plaintext in blocks or as a bit stream, techniques like substitution and transposition ciphers, weaknesses of approaches like the Hill cipher, and the history and operation of standard block ciphers.
An introductory presentation on cryptography. From ancient ciphers to modern public key encryption, it follows the evolution of a science and how it affects society.
This document summarizes the key components of encryption and decryption algorithms:
1. Plaintext is the initial intelligible message that is input into the encryption algorithm. The encryption algorithm performs substitutions and transformations on the plaintext using a secret key.
2. The secret key is independently input along with the plaintext and determines the exact substitutions and transformations performed, resulting in different ciphertext outputs for the same plaintext with different keys.
3. Ciphertext is the encrypted output that is unintelligible without the key. Decryption runs the encryption algorithm in reverse, using the ciphertext and key to recover the original plaintext.
This document discusses cryptography techniques including substitution ciphers, transposition ciphers, and advanced symmetric key methods. It provides examples of encrypting and decrypting messages using a Caesar cipher with shifting substitutions, a transposition cipher that writes messages in rows and reads them out in columns according to a keyword, and a simplified polyalphabetic cipher that shifts the substitution after each character. Frequency analysis and brute force attacks are also discussed as techniques for breaking simple ciphers.
The document discusses various polyalphabetic ciphers including the Vigenere cipher, one-time pad cipher, Playfair cipher, and Hill cipher. It provides examples of encrypting and decrypting messages with the Vigenere cipher and Playfair cipher. The Vigenere cipher uses a keyword to shift the letters of a plaintext by various amounts, while the Playfair cipher encrypts pairs of letters based on their positions in a 5x5 grid generated from a keyword. The document also describes how the Hill cipher works by converting the plaintext and keyword into matrices and performing matrix multiplication to encrypt messages in blocks of letters.
This study combines classic and modern cryptographic algorithms so that the data security of information more awake authenticity. Caesar cipher is the oldest classical cryptography which uses a symmetric key method is the key used for encryption is the same as the key used for the decryption process. Three-Pass Protocol is one of the modern cryptography where the process of sending a message does not need to distribute the key so that each party both the recipient and sender of the message does not need to know each lock. In this combination of receiving and sending messages using the Caesar Cipher algorithm for encryption and decryption, while for its delivery process using algorithms Three Pass protocol. The results from the combination of the two algorithms are to help the information sent is secure.
Jaimin chp-8 - network security-new -use this - 2011 batchJaimin Jani
The document discusses cryptography concepts including symmetric and asymmetric encryption algorithms like DES, AES, RSA. It explains the basic working principles of RSA including key generation using large prime numbers, modular arithmetic and the concept of one-way functions that make private key derivation difficult. It also covers cryptographic modes of operation like ECB, CBC that are used to encrypt data blocks of arbitrary length.
This seminar report discusses symmetric key cryptography and proposes a new symmetric key algorithm. It begins with an introduction to cryptography and the importance of security. It then describes the two main types of cryptography: symmetric key and asymmetric key. Symmetric key cryptography uses a single key for both encryption and decryption, while asymmetric key uses different public and private keys. The report proposes a new symmetric key algorithm that uses simple steps of generating binary values, reversing numbers, dividing, and adding remainders and quotients. It claims this new algorithm is well-suited for encrypting small amounts of data in a cost-effective way. The report concludes the algorithm is simple but secure due to reverse operations, and the next step is developing a public
Run-length encoding is a data compression technique that replaces consecutive repeating characters with the character and number of repeats. It can be used to compress text by replacing strings like "aabbcc" with "a2b2c2". For images, runs of pixels with the same intensity value are encoded as a pair of the run length and pixel value. Huffman coding assigns variable-length binary codes to symbols based on their frequency, with more common symbols getting shorter codes to compress data more efficiently than fixed-length codes.
This document provides an overview of cryptography concepts and techniques. It defines cryptography and its principles such as symmetric and asymmetric ciphers. It then describes various classical encryption techniques like the Caesar cipher, monoalphabetic and polyalphabetic ciphers, the Playfair cipher, Hill cipher, and the Vernam cipher. For each technique, it explains the encryption and decryption algorithms and provides examples to illustrate how they work. The document also discusses cryptanalysis techniques like brute force attacks that can be used to break certain ciphers.
The document discusses cryptography and the RSA encryption algorithm. It begins with an introduction to cryptography and its uses. It then covers the history of cryptography, common security issues, and different cryptographic techniques like symmetric and asymmetric encryption. The document focuses on explaining the RSA algorithm, how it works using public and private keys, and why factoring large numbers makes RSA secure. It provides an overview of the key aspects of cryptography and the RSA algorithm.
Mechatronics is a multidisciplinary field that refers to the skill sets needed in the contemporary, advanced automated manufacturing industry. At the intersection of mechanics, electronics, and computing, mechatronics specialists create simpler, smarter systems. Mechatronics is an essential foundation for the expected growth in automation and manufacturing.
Mechatronics deals with robotics, control systems, and electro-mechanical systems.
Open Channel Flow: fluid flow with a free surfaceIndrajeet sahu
Open Channel Flow: This topic focuses on fluid flow with a free surface, such as in rivers, canals, and drainage ditches. Key concepts include the classification of flow types (steady vs. unsteady, uniform vs. non-uniform), hydraulic radius, flow resistance, Manning's equation, critical flow conditions, and energy and momentum principles. It also covers flow measurement techniques, gradually varied flow analysis, and the design of open channels. Understanding these principles is vital for effective water resource management and engineering applications.
Null Bangalore | Pentesters Approach to AWS IAMDivyanshu
#Abstract:
- Learn more about the real-world methods for auditing AWS IAM (Identity and Access Management) as a pentester. So let us proceed with a brief discussion of IAM as well as some typical misconfigurations and their potential exploits in order to reinforce the understanding of IAM security best practices.
- Gain actionable insights into AWS IAM policies and roles, using hands on approach.
#Prerequisites:
- Basic understanding of AWS services and architecture
- Familiarity with cloud security concepts
- Experience using the AWS Management Console or AWS CLI.
- For hands on lab create account on [killercoda.com](https://killercoda.com/cloudsecurity-scenario/)
# Scenario Covered:
- Basics of IAM in AWS
- Implementing IAM Policies with Least Privilege to Manage S3 Bucket
- Objective: Create an S3 bucket with least privilege IAM policy and validate access.
- Steps:
- Create S3 bucket.
- Attach least privilege policy to IAM user.
- Validate access.
- Exploiting IAM PassRole Misconfiguration
-Allows a user to pass a specific IAM role to an AWS service (ec2), typically used for service access delegation. Then exploit PassRole Misconfiguration granting unauthorized access to sensitive resources.
- Objective: Demonstrate how a PassRole misconfiguration can grant unauthorized access.
- Steps:
- Allow user to pass IAM role to EC2.
- Exploit misconfiguration for unauthorized access.
- Access sensitive resources.
- Exploiting IAM AssumeRole Misconfiguration with Overly Permissive Role
- An overly permissive IAM role configuration can lead to privilege escalation by creating a role with administrative privileges and allow a user to assume this role.
- Objective: Show how overly permissive IAM roles can lead to privilege escalation.
- Steps:
- Create role with administrative privileges.
- Allow user to assume the role.
- Perform administrative actions.
- Differentiation between PassRole vs AssumeRole
Try at [killercoda.com](https://killercoda.com/cloudsecurity-scenario/)
Accident detection system project report.pdfKamal Acharya
The Rapid growth of technology and infrastructure has made our lives easier. The
advent of technology has also increased the traffic hazards and the road accidents take place
frequently which causes huge loss of life and property because of the poor emergency facilities.
Many lives could have been saved if emergency service could get accident information and
reach in time. Our project will provide an optimum solution to this draw back. A piezo electric
sensor can be used as a crash or rollover detector of the vehicle during and after a crash. With
signals from a piezo electric sensor, a severe accident can be recognized. According to this
project when a vehicle meets with an accident immediately piezo electric sensor will detect the
signal or if a car rolls over. Then with the help of GSM module and GPS module, the location
will be sent to the emergency contact. Then after conforming the location necessary action will
be taken. If the person meets with a small accident or if there is no serious threat to anyone’s
life, then the alert message can be terminated by the driver by a switch provided in order to
avoid wasting the valuable time of the medical rescue team.
Applications of artificial Intelligence in Mechanical Engineering.pdfAtif Razi
Historically, mechanical engineering has relied heavily on human expertise and empirical methods to solve complex problems. With the introduction of computer-aided design (CAD) and finite element analysis (FEA), the field took its first steps towards digitization. These tools allowed engineers to simulate and analyze mechanical systems with greater accuracy and efficiency. However, the sheer volume of data generated by modern engineering systems and the increasing complexity of these systems have necessitated more advanced analytical tools, paving the way for AI.
AI offers the capability to process vast amounts of data, identify patterns, and make predictions with a level of speed and accuracy unattainable by traditional methods. This has profound implications for mechanical engineering, enabling more efficient design processes, predictive maintenance strategies, and optimized manufacturing operations. AI-driven tools can learn from historical data, adapt to new information, and continuously improve their performance, making them invaluable in tackling the multifaceted challenges of modern mechanical engineering.
Build the Next Generation of Apps with the Einstein 1 Platform.
Rejoignez Philippe Ozil pour une session de workshops qui vous guidera à travers les détails de la plateforme Einstein 1, l'importance des données pour la création d'applications d'intelligence artificielle et les différents outils et technologies que Salesforce propose pour vous apporter tous les bénéfices de l'IA.
DEEP LEARNING FOR SMART GRID INTRUSION DETECTION: A HYBRID CNN-LSTM-BASED MODELijaia
As digital technology becomes more deeply embedded in power systems, protecting the communication
networks of Smart Grids (SG) has emerged as a critical concern. Distributed Network Protocol 3 (DNP3)
represents a multi-tiered application layer protocol extensively utilized in Supervisory Control and Data
Acquisition (SCADA)-based smart grids to facilitate real-time data gathering and control functionalities.
Robust Intrusion Detection Systems (IDS) are necessary for early threat detection and mitigation because
of the interconnection of these networks, which makes them vulnerable to a variety of cyberattacks. To
solve this issue, this paper develops a hybrid Deep Learning (DL) model specifically designed for intrusion
detection in smart grids. The proposed approach is a combination of the Convolutional Neural Network
(CNN) and the Long-Short-Term Memory algorithms (LSTM). We employed a recent intrusion detection
dataset (DNP3), which focuses on unauthorized commands and Denial of Service (DoS) cyberattacks, to
train and test our model. The results of our experiments show that our CNN-LSTM method is much better
at finding smart grid intrusions than other deep learning algorithms used for classification. In addition,
our proposed approach improves accuracy, precision, recall, and F1 score, achieving a high detection
accuracy rate of 99.50%.
2. 3.2
❏ To define the terms and the concepts of symmetric
key ciphers
❏ To emphasize the two categories of traditional
ciphers: substitution and transposition ciphers
❏ To describe the categories of cryptanalysis used to
break the symmetric ciphers
❏ To introduce the concepts of the stream ciphers and
block ciphers
❏ To discuss some very dominant ciphers used in the
past, such as the Enigma machine
Objectives
Chapter 3
3. 3.3
3-1 INTRODUCTION
Figure 3.1 shows the general idea behind a symmetric-key
cipher. The original message from Alice to Bob is called
plaintext; the message that is sent through the channel is
called the ciphertext. To create the ciphertext from the
plaintext, Alice uses an encryption algorithm and a shared
secret key. To create the plaintext from ciphertext, Bob
uses a decryption algorithm and the same secret key.
3.1.1 Kerckhoff’s Principle
3.1.2 Cryptanalysis
3.1.3 Categories of Traditional Ciphers
Topics discussed in this section:
7. 3.7
3.1.1 Kerckhoff’s Principle
Based on Kerckhoff’s principle, one should always
assume that the adversary, Eve, knows the
encryption/decryption algorithm. The resistance of the
cipher to attack must be based only on the secrecy of the
key.
8. 3.8
3.1.2 Cryptanalysis
As cryptography is the science and art of creating secret
codes, cryptanalysis is the science and art of breaking
those codes.
Figure 3.3 Cryptanalysis attacks
13. 3.13
3-2 SUBSTITUTION CIPHERS
A substitution cipher replaces one symbol with another.
Substitution ciphers can be categorized as either
monoalphabetic ciphers or polyalphabetic ciphers.
3.2.1 Monoalphabetic Ciphres
3.2.2 Polyalphabetic Ciphers
Topics discussed in this section:
A substitution cipher replaces one
symbol with another.
Note
14. 3.14
3.2.1 Monoalphabetic Ciphers
In monoalphabetic substitution, the
relationship between a symbol in the
plaintext to a symbol in the ciphertext is
always one-to-one.
Note
15. 3.15
3.2.1 Continued
The following shows a plaintext and its corresponding ciphertext.
The cipher is probably monoalphabetic because both l’s (els) are
encrypted as O’s.
Example 3.1
The following shows a plaintext and its corresponding ciphertext.
The cipher is not monoalphabetic because each l (el) is encrypted
by a different character.
Example 3.2
16. 3.16
3.2.1 Continued
The simplest monoalphabetic cipher is the additive cipher. This
cipher is sometimes called a shift cipher and sometimes a Caesar
cipher, but the term additive cipher better reveals its
mathematical nature.
Additive Cipher
Figure 3.8 Plaintext and ciphertext in Z26
17. 3.17
Figure 3.9 Additive cipher
3.2.1 Continued
When the cipher is additive, the
plaintext, ciphertext, and key are
integers in Z26.
Note
18. 3.18
3.2.1 Continued
Use the additive cipher with key = 15 to encrypt the message
“hello”.
Example 3.3
We apply the encryption algorithm to the plaintext, character by
character:
Solution
19. 3.19
3.2.1 Continued
Use the additive cipher with key = 15 to decrypt the message
“WTAAD”.
Example 3.4
We apply the decryption algorithm to the plaintext character by
character:
Solution
20. 3.20
3.2.1 Continued
Historically, additive ciphers are called shift ciphers. Julius Caesar
used an additive cipher to communicate with his officers. For this
reason, additive ciphers are sometimes referred to as the Caesar
cipher. Caesar used a key of 3 for his communications.
Shift Cipher and Caesar Cipher
Additive ciphers are sometimes referred
to as shift ciphers or Caesar cipher.
Note
21. 3.21
3.2.1 Continued
Eve has intercepted the ciphertext “UVACLYFZLJBYL”. Show
how she can use a brute-force attack to break the cipher.
Example 3.5
Eve tries keys from 1 to 7. With a key of 7, the plaintext is “not
very secure”, which makes sense.
Solution
23. 3.23
3.2.1 Continued
Eve has intercepted the following ciphertext. Using a statistical
attack, find the plaintext.
Example 3.6
When Eve tabulates the frequency of letters in this ciphertext, she
gets: I =14, V =13, S =12, and so on. The most common character
is I with 14 occurrences. This means key = 4.
Solution
24. 3.24
3.2.1 Continued
Multiplicative Ciphers
In a multiplicative cipher, the plaintext
and ciphertext are integers in Z26; the
key is an integer in Z26*.
Note
Figure 3.10 Multiplicative cipher
25. 3.25
3.2.1 Continued
What is the key domain for any multiplicative cipher?
Example 3.7
The key needs to be in Z26*. This set has only 12 members: 1, 3, 5,
7, 9, 11, 15, 17, 19, 21, 23, 25.
Solution
We use a multiplicative cipher to encrypt the message “hello” with
a key of 7. The ciphertext is “XCZZU”.
Example 3.8
27. 3.27
3.2.1 Continued
The affine cipher uses a pair of keys in which the first key is from
Z26* and the second is from Z26. The size of the key domain is
26 × 12 = 312.
Example 3.09
Use an affine cipher to encrypt the message “hello” with the key
pair (7, 2).
Example 3.10
28. 3.28
3.2.1 Continued
Use the affine cipher to decrypt the message “ZEBBW” with the
key pair (7, 2) in modulus 26.
Example 3.11
Solution
The additive cipher is a special case of an affine cipher in which
k1 = 1. The multiplicative cipher is a special case of affine cipher in
which k2 = 0.
Example 3.12
29. 3.29
3.2.1 Continued
Because additive, multiplicative, and affine ciphers have small key
domains, they are very vulnerable to brute-force attack.
Monoalphabetic Substitution Cipher
A better solution is to create a mapping between each plaintext
character and the corresponding ciphertext character. Alice and
Bob can agree on a table showing the mapping for each character.
Figure 3.12 An example key for monoalphabetic substitution cipher
30. 3.30
3.2.1 Continued
We can use the key in Figure 3.12 to encrypt the message
Example 3.13
The ciphertext is
31. 3.31
3.2.2 Polyalphabetic Ciphers
In polyalphabetic substitution, each occurrence of a
character may have a different substitute. The
relationship between a character in the plaintext to a
character in the ciphertext is one-to-many.
Autokey Cipher
32. 3.32
3.2.2 Continued
Assume that Alice and Bob agreed to use an autokey cipher with
initial key value k1 = 12. Now Alice wants to send Bob the message
“Attack is today”. Enciphering is done character by character.
Example 3.14
33. 3.33
3.2.2 Continued
Playfair Cipher
Figure 3.13 An example of a secret key in the Playfair cipher
Let us encrypt the plaintext “hello” using the key in Figure 3.13.
Example 3.15
35. 3.35
3.2.2 Continued
Let us see how we can encrypt the message “She is listening” using
the 6-character keyword “PASCAL”. The initial key stream is (15,
0, 18, 2, 0, 11). The key stream is the repetition of this initial key
stream (as many times as needed).
Example 3.16
36. 3.36
3.2.2 Continued
Vigenere cipher can be seen as combinations of m additive ciphers.
Example 3.17
Figure 3.14 A Vigenere cipher as a combination of m additive ciphers
37. 3.37
3.2.2 Continued
Using Example 3.18, we can say that the additive cipher is a
special case of Vigenere cipher in which m = 1.
Example 3.18
Table 3.3
A Vigenere Tableau
38. 3.38
3.2.2 Continued
Vigenere Cipher (Crypanalysis)
Let us assume we have intercepted the following ciphertext:
Example 3.19
The Kasiski test for repetition of three-character segments yields
the results shown in Table 3.4.
39. 3.39
3.2.2 Continued
Let us assume we have intercepted the following ciphertext:
Example 3.19
The Kasiski test for repetition of three-character segments yields
the results shown in Table 3.4.
40. 3.40
3.2.2 Continued
The greatest common divisor of differences is 4, which means that
the key length is multiple of 4. First try m = 4.
Example 3.19 (Continued)
In this case, the plaintext makes sense.
42. 3.42
3.2.2 Continued
For example, the plaintext “code is ready” can make a 3 × 4
matrix when adding extra bogus character “z” to the last block
and removing the spaces. The ciphertext is “OHKNIHGKLISS”.
Example 3.20
Figure 3.16 Example 3.20
43. 3.43
3.2.2 Continued
Assume that Eve knows that m = 3. She has intercepted three
plaintext/ciphertext pair blocks (not necessarily from the same
message) as shown in Figure 3.17.
Example 3.21
Figure 3.17 Example 3.21
44. 3.44
3.2.2 Continued
She makes matrices P and C from these pairs. Because P is
invertible, she inverts the P matrix and multiplies it by C to get the
K matrix as shown in Figure 3.18.
Example 3.21
Figure 3.18 Example 3.21
Now she has the key and can break any ciphertext encrypted with
that key.
(Continued)
45. 3.45
3.2.2 Continued
One of the goals of cryptography is perfect secrecy. A
study by Shannon has shown that perfect secrecy can be
achieved if each plaintext symbol is encrypted with a key
randomly chosen from a key domain. This idea is used in
a cipher called one-time pad, invented by Vernam.
One-Time Pad
48. 3.48
3-3 TRANSPOSITION CIPHERS
A transposition cipher does not substitute one symbol for
another, instead it changes the location of the symbols.
3.3.1 Keyless Transposition Ciphers
3.3.2 Keyed Transposition Ciphers
3.3.3 Combining Two Approaches
Topics discussed in this section:
A transposition cipher reorders symbols.
Note
49. 3.49
3.3.1 Keyless Transposition Ciphers
Simple transposition ciphers, which were used in the
past, are keyless.
A good example of a keyless cipher using the first method is the
rail fence cipher. The ciphertext is created reading the pattern row
by row. For example, to send the message “Meet me at the park”
to Bob, Alice writes
Example 3.22
She then creates the ciphertext “MEMATEAKETETHPR”.
50. 3.50
3.3.1 Continued
Alice and Bob can agree on the number of columns and use the
second method. Alice writes the same plaintext, row by row, in a
table of four columns.
Example 3.23
She then creates the ciphertext “MMTAEEHREAEKTTP”.
51. 3.51
3.3.1 Continued
The cipher in Example 3.23 is actually a transposition cipher. The
following shows the permutation of each character in the plaintext
into the ciphertext based on the positions.
Example 3.24
The second character in the plaintext has moved to the fifth
position in the ciphertext; the third character has moved to the
ninth position; and so on. Although the characters are permuted,
there is a pattern in the permutation: (01, 05, 09, 13), (02, 06, 10,
13), (03, 07, 11, 15), and (08, 12). In each section, the difference
between the two adjacent numbers is 4.
52. 3.52
3.3.2 Keyed Transposition Ciphers
The keyless ciphers permute the characters by using
writing plaintext in one way and reading it in another
way The permutation is done on the whole plaintext to
create the whole ciphertext. Another method is to divide
the plaintext into groups of predetermined size, called
blocks, and then use a key to permute the characters in
each block separately.
53. 3.53
3.3.2 Continued
Alice needs to send the message “Enemy attacks tonight” to Bob..
Example 3.25
The key used for encryption and decryption is a permutation key,
which shows how the character are permuted.
The permutation yields
55. 3.55
Figure 3.22 Encryption/decryption keys in transpositional ciphers
3.3.3 Continued
Keys
In Example 3.27, a single key was used in two directions for the
column exchange: downward for encryption, upward for
decryption. It is customary to create two keys.
57. 3.57
3.3.3 Continued
Using Matrices
We can use matrices to show the encryption/decryption process
for a transposition cipher.
Figure 3.24 Representation of the key as a matrix in the transposition cipher
Example 3.27
58. 3.58
Figure 3.24 Representation of the key as a matrix in the transposition cipher
3.3.3 Continued
Figure 3.24 shows the encryption process. Multiplying the 4 × 5
plaintext matrix by the 5 × 5 encryption key gives the 4 × 5
ciphertext matrix.
Example 3.27
60. 3.60
3-4 STREAM AND BLOCK CIPHERS
The literature divides the symmetric ciphers into two
broad categories: stream ciphers and block ciphers.
Although the definitions are normally applied to modern
ciphers, this categorization also applies to traditional
ciphers.
3.4.1 Stream Ciphers
3.4.2 Block Ciphers
3.4.3 Combination
Topics discussed in this section:
61. 3.61
3.4.1 Stream Ciphers
Call the plaintext stream P, the ciphertext stream C, and
the key stream K.
Figure 3.26 Stream cipher
62. 3.62
3.4.1 Continued
Additive ciphers can be categorized as stream ciphers in which the
key stream is the repeated value of the key. In other words, the
key stream is considered as a predetermined stream of keys or
K = (k, k, …, k). In this cipher, however, each character in the
ciphertext depends only on the corresponding character in the
plaintext, because the key stream is generated independently.
Example 3.30
The monoalphabetic substitution ciphers discussed in this chapter
are also stream ciphers. However, each value of the key stream in
this case is the mapping of the current plaintext character to the
corresponding ciphertext character in the mapping table.
Example 3.31
63. 3.63
3.4.1 Continued
Vigenere ciphers are also stream ciphers according to the
definition. In this case, the key stream is a repetition of m values,
where m is the size of the keyword. In other words,
Example 3.32
We can establish a criterion to divide stream ciphers based on
their key streams. We can say that a stream cipher is a
monoalphabetic cipher if the value of ki does not depend on the
position of the plaintext character in the plaintext stream;
otherwise, the cipher is polyalphabetic.
Example 3.33
64. 3.64
3.4.1 Continued
Additive ciphers are definitely monoalphabetic because ki in the
key stream is fixed; it does not depend on the position of the
character in the plaintext.
Monoalphabetic substitution ciphers are monoalphabetic
because ki does not depend on the position of the corresponding
character in the plaintext stream; it depends only on the value of
the plaintext character.
Vigenere ciphers are polyalphabetic ciphers because ki
definitely depends on the position of the plaintext character.
However, the dependency is cyclic. The key is the same for two
characters m positions apart.
Example 3.33 (Continued)
65. 3.65
3.4.2 Stream Ciphers
In a block cipher, a group of plaintext symbols of size m
(m > 1) are encrypted together creating a group of
ciphertext of the same size. A single key is used to
encrypt the whole block even if the key is made of
multiple values. Figure 3.27 shows the concept of a block
cipher.
Figure 3.27 Block cipher
66. 3.66
3.4.2 Continued
Playfair ciphers are block ciphers. The size of the block is m = 2.
Two characters are encrypted together.
Example 3.34
Hill ciphers are block ciphers. A block of plaintext, of size 2 or
more is encrypted together using a single key (a matrix). In these
ciphers, the value of each character in the ciphertext depends on
all the values of the characters in the plaintext. Although the key is
made of m × m values, it is considered as a single key.
Example 3.35
From the definition of the block cipher, it is clear that every block
cipher is a polyalphabetic cipher because each character in a
ciphertext block depends on all characters in the plaintext block.
Example 3.36
67. 3.67
3.4.3 Combination
In practice, blocks of plaintext are encrypted
individually, but they use a stream of keys to encrypt the
whole message block by block. In other words, the cipher
is a block cipher when looking at the individual blocks,
but it is a stream cipher when looking at the whole
message considering each block as a single unit.