This document discusses cryptography and the Caesar cipher. It begins by defining cryptography as the encoding of messages to achieve secure communication and outlines its goals of confidentiality, integrity, and availability. The document then describes the Caesar cipher technique, in which each letter is shifted a fixed number of positions in the alphabet. It provides an example of encrypting a message with a shift of 11. The document explains that the Caesar cipher is vulnerable to brute force and statistical cryptanalysis due to its small key space and predictable letter frequencies. It concludes that more advanced algorithms are needed for secure encryption in the digital age.
The document defines various terms related to encryption and decryption such as encryption, decryption, cryptosystem, plaintext, and ciphertext. It describes different types of encryption algorithms including symmetric encryption which uses the same key for encryption and decryption, and asymmetric encryption which uses different keys. It also explains different encryption methods such as substitution ciphers including monoalphabetic and polyalphabetic substitutions as well as transposition ciphers. The Caesar cipher and Vigenère cipher are provided as examples. Factors that can be analyzed to cryptanalyze ciphers are also outlined.
The document provides information on classical encryption techniques, specifically covering symmetric cipher models, cryptography, cryptanalysis, and attacks. It discusses substitution and transposition techniques, including the Caesar cipher, monoalphabetic cipher, and Playfair cipher. For each technique, it explains the encryption and decryption process, cryptanalysis methods, and provides examples to illustrate how the techniques work.
This document discusses cryptography and its history. Cryptography began as early as 2000 BC in Egypt and has evolved over three eras: the manual era involving pen and paper ciphers, the mechanical era with the invention of cipher machines, and the modern era utilizing computers. Modern cryptography combines computer science and mathematics to encrypt data for security. Key aspects include encryption, decryption, symmetric and asymmetric keys, and different cipher algorithms. The document also covers categories of cryptography, notable cryptographers, applications, and some limitations of early cryptography techniques.
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.
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.
The presentation include:
-Diffie hellman key exchange algorithm
-Primitive roots
-Discrete logarithm and discrete logarithm problem
-Attacks on diffie hellman and their possible solution
-Key distribution center
This document provides an overview of cryptography. It begins with a brief history of cryptography from ancient times to modern computer cryptography. It then defines basic concepts like encryption, decryption, plaintext and ciphertext. It describes different types of cryptography including codes, ciphers, steganography and computer ciphers. It also discusses cryptanalysis, security mechanisms like encryption, digital signatures and hash algorithms. It concludes by explaining applications of cryptography in daily life like emails and secured communication between family members.
Cryptography involves secret writing and encrypting messages so that only authorized parties can read them. It uses algorithms and keys to encrypt plaintext into ciphertext. Cryptanalysis involves breaking ciphers, while cryptography is designing ciphers. Cryptology encompasses both cryptography and cryptanalysis. Common encryption models involve plaintext being encrypted into ciphertext using a key, which is then transmitted and decrypted by the intended receiver using the same key.
The document defines various terms related to encryption and decryption such as encryption, decryption, cryptosystem, plaintext, and ciphertext. It describes different types of encryption algorithms including symmetric encryption which uses the same key for encryption and decryption, and asymmetric encryption which uses different keys. It also explains different encryption methods such as substitution ciphers including monoalphabetic and polyalphabetic substitutions as well as transposition ciphers. The Caesar cipher and Vigenère cipher are provided as examples. Factors that can be analyzed to cryptanalyze ciphers are also outlined.
The document provides information on classical encryption techniques, specifically covering symmetric cipher models, cryptography, cryptanalysis, and attacks. It discusses substitution and transposition techniques, including the Caesar cipher, monoalphabetic cipher, and Playfair cipher. For each technique, it explains the encryption and decryption process, cryptanalysis methods, and provides examples to illustrate how the techniques work.
This document discusses cryptography and its history. Cryptography began as early as 2000 BC in Egypt and has evolved over three eras: the manual era involving pen and paper ciphers, the mechanical era with the invention of cipher machines, and the modern era utilizing computers. Modern cryptography combines computer science and mathematics to encrypt data for security. Key aspects include encryption, decryption, symmetric and asymmetric keys, and different cipher algorithms. The document also covers categories of cryptography, notable cryptographers, applications, and some limitations of early cryptography techniques.
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.
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.
The presentation include:
-Diffie hellman key exchange algorithm
-Primitive roots
-Discrete logarithm and discrete logarithm problem
-Attacks on diffie hellman and their possible solution
-Key distribution center
This document provides an overview of cryptography. It begins with a brief history of cryptography from ancient times to modern computer cryptography. It then defines basic concepts like encryption, decryption, plaintext and ciphertext. It describes different types of cryptography including codes, ciphers, steganography and computer ciphers. It also discusses cryptanalysis, security mechanisms like encryption, digital signatures and hash algorithms. It concludes by explaining applications of cryptography in daily life like emails and secured communication between family members.
Cryptography involves secret writing and encrypting messages so that only authorized parties can read them. It uses algorithms and keys to encrypt plaintext into ciphertext. Cryptanalysis involves breaking ciphers, while cryptography is designing ciphers. Cryptology encompasses both cryptography and cryptanalysis. Common encryption models involve plaintext being encrypted into ciphertext using a key, which is then transmitted and decrypted by the intended receiver using the same key.
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.
The document discusses the history and concepts of encryption, including ancient encryption methods like hieroglyphs and the Caesar cipher. It then covers modern digital encryption, describing how public/private key encryption works using plaintexts, ciphertexts, encryption/decryption keys, and algorithms. The document also discusses hash values, digital signatures, types of attacks against encryption, different cipher implementations like DES and AES, and reasons why attacks can still succeed despite encryption.
This document discusses conventional encryption principles and algorithms. It covers the following key points:
1) Conventional encryption uses an encryption algorithm, secret key, and decryption algorithm to encrypt plaintext into ciphertext and decrypt ciphertext back to plaintext. The security depends on keeping the key secret, not the algorithm.
2) Common symmetric encryption algorithms discussed include DES, Triple DES, Blowfish, RC5, and CAST-128. Key sizes and number of rounds are important parameters for security.
3) Modes of operation like cipher block chaining are used to encrypt blocks of plaintext. Encryption can be done at the link level, end-to-end, or both for added security.
4)
The Caesar cipher is one of the earliest known substitution ciphers. It works by shifting each letter in a plaintext message by a set number of positions (the key) in the alphabet to encrypt it. For example, with a key of 3, A would be replaced by D, B by E, and so on. Decryption simply requires shifting letters in the opposite direction by the same key. While simple, the Caesar cipher has some mathematical properties and was allegedly used by Julius Caesar to communicate with his army. However, it is also easy to break through brute force by trying all 26 possible keys.
Principles of public key cryptography and its UsesMohsin Ali
This document discusses the principles of public key cryptography. It begins by defining asymmetric encryption and how it uses a public key and private key instead of a single shared key. It then discusses key concepts like digital certificates and public key infrastructure. The document also provides examples of how public key cryptography can be used, including the RSA algorithm and key distribution methods like public key directories and certificates. It explains how public key cryptography solves the key distribution problem present in symmetric encryption.
This document provides an overview of cryptography. It begins with background information, defining cryptography as using mathematics to encrypt and decrypt data to enable secure transmission. The main purposes of cryptography are then outlined as authentication, privacy/confidentiality, integrity, and non-repudiation. The methodology section describes symmetric and asymmetric encryption methods. Symmetric encryption uses the same key for encryption and decryption while asymmetric uses mathematically related public/private key pairs. Specific symmetric algorithms like block and stream ciphers are then defined along with concepts like padding schemes. The document concludes with sections on key exchange and digital signatures, which enable practical uses of cryptography.
The document discusses classical encryption techniques such as the Caesar cipher, monoalphabetic ciphers, the Playfair cipher, and polyalphabetic ciphers. It explains the basic principles of how each technique works to encrypt plaintext into ciphertext and highlights some of their weaknesses, such as being vulnerable to frequency analysis for the monoalphabetic ciphers. The document also introduces block ciphers and stream ciphers as two general categories of encryption algorithms.
DES was developed as a standard for communications and data protection by an IBM research team in response to a request from the National Bureau of Standards (now called NIST). DES uses the techniques of confusion and diffusion achieved through numerous permutations and the XOR operation. The basic DES process encrypts a 64-bit block using a 56-bit key over 16 complex rounds consisting of permutations and key-dependent calculations. Triple DES was developed as a more secure version of DES.
1) The document discusses various transposition ciphers including the rail fence cipher, route cipher, simple columnar transposition, and double transposition cipher. It explains how each cipher works through encrypting and decrypting sample messages.
2) Detection methods for transposition ciphers are also covered, such as frequency analysis and finding anagrams in the ciphertext. Simpler transposition ciphers can be vulnerable to these kinds of cryptanalysis techniques.
3) Genetic algorithms are mentioned as a way for cryptanalysts to find the most likely decryption key through probability calculations.
The presentation describes basics of cryptography and information security. It covers goals of cryptography, history of cipher symmetric and public key cryptography
The Diffie-Hellman algorithm was developed by Whitfield Diffie and Martin Hellman in 1976.
This algorithm was devices not to encrypt the data but to generate same private cryptographic key at both ends so that there is no need to transfer this key from one communication end to another.
Diffie – Hellman algorithm is an algorithm that allows two parties to get the shared secret key using the communication channel, which is not protected from the interception but is protected from modification.
- Substitution techniques involve replacing the letters of plaintext with other letters, numbers or symbols. The main substitution techniques are Caesar cipher, monoalphabetic cipher, Playfair cipher and Hill cipher.
- The Caesar cipher replaces each letter with the letter three positions down the alphabet. The monoalphabetic cipher uses a single alphabetic key for the entire message. The Playfair cipher encrypts pairs of letters based on a 5x5 grid generated from a keyword. The Hill cipher encrypts blocks of letters as numerical values using a matrix-based approach.
This document provides an overview of classical encryption techniques, including symmetric encryption and cryptanalysis. It discusses the basic components of encryption (plaintext, ciphertext, cipher, key) and encryption mappings. Specifically, it examines the requirements for secure symmetric encryption using a strong algorithm and secret key known only to the sender and receiver. It also covers cryptanalytic attacks, the strength of encryption algorithms, and basic techniques like brute force search and classical substitution ciphers.
Cryptography involves encrypting and decrypting information using algorithms and keys. There are two main types: public key cryptography uses different keys for encryption and decryption while private (symmetric) key cryptography uses the same key. Digital signatures provide authentication by encrypting a hash of a message with a private key so receivers can validate the sender. Key management and distribution present challenges to ensure secrecy and prevent unauthorized access.
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)
RSA is a public-key cryptosystem that uses both public and private keys for encryption and decryption. It was the first practical implementation of such a cryptosystem. The algorithm involves four main steps: 1) generation of the public and private keys, 2) encryption of messages using the public key, 3) decryption of encrypted messages using the private key, and 4) potential cracking of the encrypted message. It works by using two large prime numbers to generate the keys and performs exponentiation and modulo operations on messages to encrypt and decrypt them. There were some drawbacks to the original RSA algorithm related to redundant calculations and representing letters numerically that opened it up to easier hacking. Enhancements to RSA improved it by choosing
This document discusses data encryption methods. It defines encryption as hiding information so it can only be accessed by those with the key. There are two main types: symmetric encryption uses one key, while asymmetric encryption uses two different but related keys. Encryption works by scrambling data using techniques like transposition, which rearranges the order, and substitution, which replaces parts with other values. The document specifically describes the Data Encryption Standard (DES) algorithm and the public key cryptosystem, which introduced the innovative approach of using different keys for encryption and decryption.
This document provides an introduction to cryptography and cryptanalysis. It contains a table of contents outlining the topics to be covered, which include the history and concepts of cryptography, symmetric and public key cryptosystems, cryptanalysis techniques, and applications of cryptography such as digital signatures and internet security protocols. The author thanks several people who provided input and acknowledges that any mistakes are their own. It also includes a crash course on basic number theory concepts relevant to 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.
The document discusses the history and concepts of encryption, including ancient encryption methods like hieroglyphs and the Caesar cipher. It then covers modern digital encryption, describing how public/private key encryption works using plaintexts, ciphertexts, encryption/decryption keys, and algorithms. The document also discusses hash values, digital signatures, types of attacks against encryption, different cipher implementations like DES and AES, and reasons why attacks can still succeed despite encryption.
This document discusses conventional encryption principles and algorithms. It covers the following key points:
1) Conventional encryption uses an encryption algorithm, secret key, and decryption algorithm to encrypt plaintext into ciphertext and decrypt ciphertext back to plaintext. The security depends on keeping the key secret, not the algorithm.
2) Common symmetric encryption algorithms discussed include DES, Triple DES, Blowfish, RC5, and CAST-128. Key sizes and number of rounds are important parameters for security.
3) Modes of operation like cipher block chaining are used to encrypt blocks of plaintext. Encryption can be done at the link level, end-to-end, or both for added security.
4)
The Caesar cipher is one of the earliest known substitution ciphers. It works by shifting each letter in a plaintext message by a set number of positions (the key) in the alphabet to encrypt it. For example, with a key of 3, A would be replaced by D, B by E, and so on. Decryption simply requires shifting letters in the opposite direction by the same key. While simple, the Caesar cipher has some mathematical properties and was allegedly used by Julius Caesar to communicate with his army. However, it is also easy to break through brute force by trying all 26 possible keys.
Principles of public key cryptography and its UsesMohsin Ali
This document discusses the principles of public key cryptography. It begins by defining asymmetric encryption and how it uses a public key and private key instead of a single shared key. It then discusses key concepts like digital certificates and public key infrastructure. The document also provides examples of how public key cryptography can be used, including the RSA algorithm and key distribution methods like public key directories and certificates. It explains how public key cryptography solves the key distribution problem present in symmetric encryption.
This document provides an overview of cryptography. It begins with background information, defining cryptography as using mathematics to encrypt and decrypt data to enable secure transmission. The main purposes of cryptography are then outlined as authentication, privacy/confidentiality, integrity, and non-repudiation. The methodology section describes symmetric and asymmetric encryption methods. Symmetric encryption uses the same key for encryption and decryption while asymmetric uses mathematically related public/private key pairs. Specific symmetric algorithms like block and stream ciphers are then defined along with concepts like padding schemes. The document concludes with sections on key exchange and digital signatures, which enable practical uses of cryptography.
The document discusses classical encryption techniques such as the Caesar cipher, monoalphabetic ciphers, the Playfair cipher, and polyalphabetic ciphers. It explains the basic principles of how each technique works to encrypt plaintext into ciphertext and highlights some of their weaknesses, such as being vulnerable to frequency analysis for the monoalphabetic ciphers. The document also introduces block ciphers and stream ciphers as two general categories of encryption algorithms.
DES was developed as a standard for communications and data protection by an IBM research team in response to a request from the National Bureau of Standards (now called NIST). DES uses the techniques of confusion and diffusion achieved through numerous permutations and the XOR operation. The basic DES process encrypts a 64-bit block using a 56-bit key over 16 complex rounds consisting of permutations and key-dependent calculations. Triple DES was developed as a more secure version of DES.
1) The document discusses various transposition ciphers including the rail fence cipher, route cipher, simple columnar transposition, and double transposition cipher. It explains how each cipher works through encrypting and decrypting sample messages.
2) Detection methods for transposition ciphers are also covered, such as frequency analysis and finding anagrams in the ciphertext. Simpler transposition ciphers can be vulnerable to these kinds of cryptanalysis techniques.
3) Genetic algorithms are mentioned as a way for cryptanalysts to find the most likely decryption key through probability calculations.
The presentation describes basics of cryptography and information security. It covers goals of cryptography, history of cipher symmetric and public key cryptography
The Diffie-Hellman algorithm was developed by Whitfield Diffie and Martin Hellman in 1976.
This algorithm was devices not to encrypt the data but to generate same private cryptographic key at both ends so that there is no need to transfer this key from one communication end to another.
Diffie – Hellman algorithm is an algorithm that allows two parties to get the shared secret key using the communication channel, which is not protected from the interception but is protected from modification.
- Substitution techniques involve replacing the letters of plaintext with other letters, numbers or symbols. The main substitution techniques are Caesar cipher, monoalphabetic cipher, Playfair cipher and Hill cipher.
- The Caesar cipher replaces each letter with the letter three positions down the alphabet. The monoalphabetic cipher uses a single alphabetic key for the entire message. The Playfair cipher encrypts pairs of letters based on a 5x5 grid generated from a keyword. The Hill cipher encrypts blocks of letters as numerical values using a matrix-based approach.
This document provides an overview of classical encryption techniques, including symmetric encryption and cryptanalysis. It discusses the basic components of encryption (plaintext, ciphertext, cipher, key) and encryption mappings. Specifically, it examines the requirements for secure symmetric encryption using a strong algorithm and secret key known only to the sender and receiver. It also covers cryptanalytic attacks, the strength of encryption algorithms, and basic techniques like brute force search and classical substitution ciphers.
Cryptography involves encrypting and decrypting information using algorithms and keys. There are two main types: public key cryptography uses different keys for encryption and decryption while private (symmetric) key cryptography uses the same key. Digital signatures provide authentication by encrypting a hash of a message with a private key so receivers can validate the sender. Key management and distribution present challenges to ensure secrecy and prevent unauthorized access.
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)
RSA is a public-key cryptosystem that uses both public and private keys for encryption and decryption. It was the first practical implementation of such a cryptosystem. The algorithm involves four main steps: 1) generation of the public and private keys, 2) encryption of messages using the public key, 3) decryption of encrypted messages using the private key, and 4) potential cracking of the encrypted message. It works by using two large prime numbers to generate the keys and performs exponentiation and modulo operations on messages to encrypt and decrypt them. There were some drawbacks to the original RSA algorithm related to redundant calculations and representing letters numerically that opened it up to easier hacking. Enhancements to RSA improved it by choosing
This document discusses data encryption methods. It defines encryption as hiding information so it can only be accessed by those with the key. There are two main types: symmetric encryption uses one key, while asymmetric encryption uses two different but related keys. Encryption works by scrambling data using techniques like transposition, which rearranges the order, and substitution, which replaces parts with other values. The document specifically describes the Data Encryption Standard (DES) algorithm and the public key cryptosystem, which introduced the innovative approach of using different keys for encryption and decryption.
This document provides an introduction to cryptography and cryptanalysis. It contains a table of contents outlining the topics to be covered, which include the history and concepts of cryptography, symmetric and public key cryptosystems, cryptanalysis techniques, and applications of cryptography such as digital signatures and internet security protocols. The author thanks several people who provided input and acknowledges that any mistakes are their own. It also includes a crash course on basic number theory concepts relevant to cryptography.
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.
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.
Symmetric encryption uses a single, shared key between the sender and receiver to encrypt and decrypt messages. Common symmetric algorithms are DES, 3DES, and AES. The main drawback is securely exchanging the encryption key between parties. Cryptanalysis is the study of decrypting ciphertext without knowing the key, and involves cryptanalytic attacks or brute-force attacks to discover the plaintext or key.
The document summarizes classical encryption techniques, including:
- Symmetric encryption uses a shared key between sender and receiver for encryption/decryption.
- Early techniques included the Caesar cipher (shifting letters), monoalphabetic cipher (mapping each letter to another), and Playfair cipher (encrypting letter pairs).
- The Vigenère cipher improved security by using a keyword to select different Caesar ciphers for successive letters, making it a polyalphabetic cipher.
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 provides an overview of cryptography from classical to modern times. It discusses the history and evolution of cryptographic techniques including substitution ciphers, transposition ciphers, codes, public key cryptography, digital signatures, and key distribution problems. The document also summarizes the four main topics that will be covered in the course: the history and foundations of modern cryptography, using cryptography in practice, the theory of cryptography including proofs and definitions, and a special topic in cryptography.
This document provides an overview of cryptography and encryption techniques. It discusses the basic cryptographic terms and historical background of cryptography. It then describes different cipher techniques including transposition cipher and substitution cipher. It also discusses conventional encryption algorithms such as DES, AES, and RSA. Symmetric key cryptography and public key cryptography are explained. The document also covers digital signatures, cryptanalysis, and cryptographic systems in general.
Today in modern era of internet we share some sensitive data to information transmission. but need to ensure security. So we focus on Cryptography modern technique for secure transmission of information over network.
Cryptography is the process of securing communication and information. This document discusses several methods of cryptography including symmetric and public key cryptography. It provides examples of classical cryptography techniques like the Caesar cipher, transposition cipher, substitution cipher and the Vigenere cipher. It also discusses modern symmetric key algorithms like the Data Encryption Standard (DES) and the Advanced Encryption Standard (AES) which are widely used today. The one-time pad is described as theoretically unbreakable but impractical to implement. Block ciphers and padding methods are also summarized.
This document provides an overview of cryptography and this course on the subject. It discusses the history of cryptography, examples throughout history of codes being invented and then broken, and modern cryptography since the 1970s which focuses on provable security. The course will cover foundations and principles, definitions and proofs of security, applications, and advanced topics like public key cryptography and zero-knowledge proofs. It provides information about lectures, prerequisites, readings, assignments, and notes that cryptography is a challenging subject involving mathematical proofs.
The document provides an overview of cryptography concepts including symmetric and asymmetric encryption algorithms. Symmetric algorithms discussed include the Caesar cipher, Vigenere cipher, DES, AES and their strengths/weaknesses. Asymmetric algorithms discussed include Diffie-Hellman key exchange and RSA public-key cryptography. The document also summarizes how encryption techniques like AES and RSA can be used to securely transmit messages between two parties over an insecure network.
Encryption obscures information to authorize access while hiding it from others. Private key encryption uses a shared key while public key encryption uses separate keys for encryption and decryption. Digital signatures authenticate information through encryption with a private key. Key management creates, distributes, certifies, protects, and revokes keys, while hierarchical and web of trust models establish trust in encryption systems.
The document provides an overview of classical encryption techniques, including: symmetric ciphers that use the same key for encryption and decryption (such as the Caesar cipher, monoalphabetic ciphers like the Playfair cipher, and polyalphabetic ciphers like the Vigenère cipher) as well as transposition techniques that rearrange plaintext; rotor machines like the Enigma that implemented complex polyalphabetic substitution; and steganography that hides messages within other files like images. The goal is to introduce basic concepts of encryption to prepare for studying modern cryptography.
Classical Encryption Techniques in Network Securitybabak danyal
The document provides an overview of classical encryption techniques, including: symmetric ciphers that use the same key for encryption and decryption (such as the Caesar cipher, monoalphabetic ciphers like the Playfair cipher, and polyalphabetic ciphers like the Vigenère cipher) as well as transposition techniques that rearrange plaintext; rotor machines like the Enigma that implemented complex polyalphabetic substitution; and steganography that hides messages within other files or messages. The goal is to introduce basic concepts and terminology of encryption to prepare for studying modern cryptography.
This document provides an overview of cryptography. It begins with basic definitions related to cryptography and a brief history of its use from ancient times to modern ciphers. It then describes different types of ciphers like stream ciphers, block ciphers, and public key cryptosystems. It also covers cryptography methods like symmetric and asymmetric algorithms. Common types of attacks on cryptosystems like brute force, chosen ciphertext, and frequency analysis are also discussed.
1) DES is a block cipher developed in the 1970s that became a standard but is now considered insecure due to advances in computing power allowing brute force attacks on its 56-bit key.
2) DES uses a Feistel network structure applying 16 rounds of substitution and permutation. The key is used to generate 48-bit round keys for each round.
3) Common modes of operation for DES include ECB, CBC, CFB and OFB which specify how the cipher is applied to multiple blocks of plaintext. CTR mode is considered the best as it allows parallel encryption of blocks.
1) DES is a block cipher developed in the 1970s that became a standard but is now considered insecure due to advances in computing power allowing brute force attacks on its 56-bit key.
2) DES uses a Feistel network structure applying 16 rounds of substitution and permutation. The key is used to generate 48-bit round keys for each round.
3) While initially secure, concerns were raised about the small key size of DES and whether the NSA could exploit "trapdoors". Alternatives like triple-DES were developed to increase security.
The document discusses linear feedback shift registers and their use in generating pseudorandom numbers for use as cryptographic keys. It describes how linear feedback shift registers can be cracked using known plaintext attacks if the plaintext and ciphertext are known. It then discusses ways to strengthen cryptography systems, including through the use of confusion and diffusion techniques. Finally, it provides an overview of the DES cryptosystem, including its history, design, and some criticisms of its security.
Similar to Introductory Lecture on Cryptography and Information Security (20)
Introductory Lecture on Cryptography and Information Security
1. Dr. Bikramjit Sarkar
Associate Professor
Dept. of Computer Science and Engineering
Techno India – Salt Lake
Kolkata, India.
Email: sarkar.Bikramjit@gmail.com
2. “THREE PEOPLE CAN KEEP A SECRET IF
TWO OF THEM ARE DEAD!”
- Benjamin Franklin
Human tendency is that when told that something
is secret and asked to keep it secret, people
become quite eager to share that secret to
everyone else.
Keeping secret is not that easy...
3. We are living in the Information age where there is
a need to keep information of every aspect of life.
And the information, like any other asset, needs
to be secured.
With the advent of computers, information storage
became electronic. And a need for computer
security became a real challenge.
4. Security goals:
Confidentiality – Information needs to be
hidden from unauthorized access.
Integrity – Information needs to be protected
from unauthorized alteration.
Availability – Information needs to be available
to authorized entity, as and when required.
5. The actual implementation of the security goals
needs some techniques. Two techniques are
prevalent today:
Cryptography – Concealing the contents of a
message by enciphering.
Steganography – Concealing the message itself
by covering it with something else.
6. Cryptography
Cryptography (or cryptology), a word with Greek
origin (Secret Writing), is the art and science
towards achieving information security by
encoding (enciphering) the original message to
some non-readable form.
It is about constructing and analyzing protocols
that overcome the influence of adversaries,
considering various security goals.
7. Cryptography – contd..
The sender, say Alice, encodes (encrypts) the
original message (plain text) into some non-
readable form (cipher text) and transmit the
cipher text over the communication channel.
The receiver, say Bob, receives the cipher text and
decodes (decrypts) the cipher text to its original
form (plain text).
Nevertheless, there is a high probability that the
intruder, say Oscar, listens to the
communication.
8. Cryptography – contd..
Although, in the past, cryptography referred only
to the encryption and decryption of messages
using secret keys, today it is defined as involving
three distinct mechanisms:
Symmetric-key cryptography (Classical)
Asymmetric-key cryptography
Hashing
9. Cryptography – contd..
Symmetric-key cryptography uses a single
secret key for both encryption and decryption.
Here encryption / decryption can be thought of as
electronic locking / unlocking. Alice puts the
message in a box and locks the box using the
shared secret key. Bob unlocks the box with the
same key and takes out the message. It is
assumed that Oscar cannot understand the content
of the transmitted message by simply
eavesdropping over the channel.
10. Cryptography – contd..
Asymmetric-key cryptography works on a pair
of keys instead of a single key: one public key and
one private key.
Here Bob generates one public key and one private
key and broadcasts the public key. Alice encrypts
the message with Bob’s public key and transmits
over the channel. At the receiver end, Bob decrypts
the encrypted message by the private key and gets
back the original message.
11. Cryptography – contd..
Hashing is a technique where fixed-length
message digests are obtained out of variable
length messages using some cryptographic hash
functions.
Here Alice sends both the message and the
message digest to Bob to provide check values.
12. Classical Cryptography – Definition
The crypto-system is a 5-tuple: (P, C, K, E, D), where,
P is a finite set of possible plaintexts
C is a finite set of possible cipher texts
K is a finite set of possible keys (key space)
For each k € K, there exist one encryption rule ek€ E
and one decryption rule dk€ D, such that,
ek (x) = y and dk (y) = x, where, x € P and y € C .
dk (ek (x)) = x
14. Classical Cryptography – Properties
Encryption rules and Decryption rules should
be computable.
Given a cipher text, it should be difficult for an
opponent to identify the encryption key and hence
the plaintext.
For the last to hold, the key space must be
large enough. Otherwise, the intruder might be
able to iterate through all the keys (brute-force
attack).
15. Classical Cryptography – Caesar cipher
Caesar cipher, also known as Caesar's cipher,
the shift cipher, Caesar's code or Caesar shift, is
one of the simplest and most widely
known encryption technique. It is a type
of substitution cipher in which each letter in
the plaintext is replaced by a letter some fixed
number of positions down the alphabet. For
example, with a right / left shift of 3, D would be
replaced by G / A, E would become H / B, and so
on. The method is named after Julius Caesar,
who used it in his private correspondence.
16. Caesar cipher – Computation
P = C = K = Z26 = {0, 1, 2, ..., 24, 25}
For simplicity, remove spaces and consider only upper
case characters of English alphabet and each character
is assigned with the numeric values as follows:
A = 0, B = 1, C = 2, ..., X = 23, Y = 24, Z = 25.
ek € E: y = ek (x) = (x + k) mod 26
dk € D: x = dk (y) = (y – k) mod 26} x, y, k € Z26
17. Caesar cipher – Illustration
Let us consider the key k = 11 and the original
message (plaintext) WEWILLMEET
So, the sequence of corresponding integers
xi: 22 – 4 – 22 – 8 – 11 – 11 – 12 – 4 – 4 – 19
ek € E: yi = ek (xi) = (xi + 11) mod 26
yi : 7 – 15 – 7 – 19 – 22 – 22 – 23 – 15 – 15 – 4
So, the sequence of corresponding characters
(cipher text): HPHTWWXPPE
The plaintext can be obtained back by the
decryption rule dk € D: xi = dk (yi) = (y – k) mod 26
So, dk: HPHTWWXPPE → WEWILLMEET
18. Caesar cipher – Cryptanalysis
It should be noted that the enciphering
algorithms are public but what makes the
crypto-system applicable is the secrecy of the
key. Cryptanalysis refers to the process of
computing the key, which is concerned to the
intruders.
Caesar cipher is vulnerable mainly to two types of
attacks (cryptanalysis):
Brute-force attack
Statistical attack
19. Caesar cipher – Brute-force attack
The Caesar cipher is vulnerable to brute-force
attacks that uses exhaustive key searches.
The key-domain of the Caesar cipher is very
small. Only 26 possible keys are there, out of
which 0 is useless.
This leaves only 25 possible keys for encryption /
decryption.
The intruder can easily launch a brute-force
attack on the cipher text.
20. Brute-force attack: example
Let us consider that Oscar has intercepted the
cipher text UVACLYFZLJBYL. Now Oscar will
keep trying with all possible keys (1 to 25) and
with the key 7, he will find a character-sequence
NOTVERYSECURE which makes sense (Plaintext).
Key Plaintext
1 TUZBKXEYKIAXK
2 STYAJWDXJHZWJ
3 RSXZIVCWIGYVI
4 QRWYHUBVHFXUH
5 PQVXGTAUGEWTG
6 OPUWFSZTFDVSF
7 NOTVERYSECURE
21. Caesar cipher – Statistical attack
The Caesar cipher is also subject to statistical
attacks that uses the frequency of occurrence of
characters for a particular language.
Frequency of occurrence of letters (English)
Letter Frequency Letter Frequency Letter Frequency Letter Frequency
E 12.7 H 6.1 W 2.3 K 0.08
T 9.1 R 6.0 F 2.2 J 0.02
A 8.2 D 4.3 G 2.0 Q 0.01
O 7.5 L 4.0 Y 2.0 X 0.01
I 7.0 C 2.8 P 1.9 Z 0.01
N 6.7 U 2.8 B 1.5
S 6.3 M 2.4 V 1.0
22. Statistical attack: example
Let us consider that Oscar has intercepted the
cipher text as follows:
XLILSYWIMWRSAJSVWEPIJSVJSYVQMPPMSRHS
PPEVWMXMWASVXLQSVILYVVCFIJSVIXLIWIPPIV
VIGIMZIWQSVISJJIVW
Oscar now tabulates the frequency of letters in the
cipher text and gets I = 14, V = 13, S = 12 and so
on.
23. Statistical attack: example – contd..
This shows that the character I in the cipher text
has the highest frequency of occurrence.
Oscar, therefore, makes a prediction that the
character I in the cipher text probably
corresponds to the character E in the plain text.
And hence the key is possibly 4. With the key of
value 4 if the cipher text is decrypted, it becomes
readable (plaintext):
THEHOUSEISNOWFORSALEFORFOURMILLIOND
OLLARSITISWORTHMOREHURRYBEFORETHESE
LLERRECEIVESMOREOFFERS
24. Conclusion
It is, therefore, prevalent that the Caesar cipher is
not that efficient to be applicable towards
information security in this electronic age. So,
there is a need of more efficient and secure
algorithms.
Due to several reports of failure of different
enciphering algorithms, ultimately Rijndael won
the competition and got selected as Advanced
Encryption Standards by NIST in 2001 – 2002.
But no algorithm has been able to provide
ultimate security.