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{` Kelly School of Business Indiana University Information Systems Graduate Programs `}
Part 1 – Introduction and Concepts
Introduction
 Cryptography is used to hide data – to render data unintelligible through its transformation into an unreadable state  and to ensure that data has not been altered in transit. It can also be used to ensure the authenticity of the data as well as the authenticity of the data source.
 Cryptography supports confidentiality, integrity and authenticity in{" "}
 cryptography homework help
 It does not support availability
Cryptography concepts
 Plaintext or Cleartext
 The original message
 Readable by attacker
 Ciphertext or cryptogram

Altered message that is unreadable to anyone except the
intended recipients Unreadable by attacker
 Encryption / enciphering
 The process of converting plaintext to ciphertext
 Decryption / deciphering
 The reverse of encryption – going from ciphertext to plaintext using the cryptographic algorithm and the key
 Algorithm
 Mathematical function used in the encryption and decryption process
Figure 3.1 The cryptographic process
 Key or Cryptovariable
 The sequence that controls the operation of the cryptographic algorithm
 Determines behavior of algorithm and permits reliable encryption and decryption of the message
 Keys can be private (secret) or public
 Nonrepudiation
 A security service by which evidence is maintained so that the sender and the receiver of data cannot deny having participated in the communication
 Nonrepudiation is associated with digital signature keys and digital certificates
 Non repudiation of origin
 Non repudiation of receipt
 Cryoptosystem
 The entire cryptographic operation
 Includes the algorithm, the key and key management functions
 Cryptanalysis
 Study of techniques for defeating cryptographic techniques and by extension security services
 Cryptology
 Science that deals with hidden, disguised or encrypted communications
 Includes communications security and communications intelligence
 Collision
 Occurs when a hash function generates the same output for different inputs
 Key space
 The total number of possible values of keys in a cryptographic algorithm or other security mechanism (such as password; numbers generated by smart cards).
 Key space = 2^{n }where n = length of key in bits
 Work factor
 Time and effort required to break a protective measure
 Initialization Vector (IV)
 Nonsecret binary vector (block of bits) used as the initializing input for the encryption of a plaintext sequence
 Increases security by introducing additional cryptographic variance to create unique ciphertext using the same key
 Also used to synchronize cryptographic equipment
 IV must be known to the recipient to decrypt message
 Encoding
 Action of changing a message to another format through the use of a code.
 Usually used for transmission or storage
 Used for message integrity as opposed to confidentiality
 Decoding
 Reverse of encoding: converting encoded message into its plaintext format
 Transposition or permutation
 Reordering plaintext to hide the message
 Substitution
 The process of exchanging one letter (or byte) for another
 SPNetwork
 Substitution and Permutation
 Adds confusion and diffusion to the process
 Confusion
 Provided by mixing/changing the key values used during the repeated rounds of encryption
 Key is changed for each round of encryption
 Makes it very hard to find the key even if we have a large amount of plaintext/ciphertext pairs encrypted using the same key
 Diffusion
 Mixing up the location of the plaintext throughout the ciphertext
 Location of first character of plaintext may change several times during the encryption process due to transposition
 Good diffusion means that if one bit of the plaintext is changed, then the ciphertext should change completely
 Avalanche Effect
 Designing algorithms where a minor change in either the key or the plaintext will have a significant change in the resulting ciphertext
 A feature of a strong hashing function
Protecting Data
 Data Storage
 Data Transmission
 Link encryption vs. end to end encryption
Methods of Cryptography
 Methods of encrypting data
 Stream
 Encrypts data one bit at a time
 Block
 Encrypts data one block at a time
Exclusive OR (XOR)
 XOR is a Boolean function very commonly used in cryptographic operations
 A binary operation that adds two binary values together
 If the values added are the same, output is 0
 If the values added are different, output is 1
{` Plain text 0101001 Encryption keystream 01110011 Cipher text 00100010 `}
Stream Based Cipher
 A stream based cipher mixes (XOR) the plaintext with a keystream that is generated by the cryptosystem
 Streambased ciphers work primarily on substitution
 Keystream must be strong (long) enough to be not easily guessed because the keystream will repeat after a while
 The strength of the cipher depends on specific implementation
 Key management processes must be secure
Block Ciphers
 Operates on blocks of plaintext
 Blocks sizes are usually multiples of 8
 Most block ciphers use a combination of substitution and transposition to perform their operations
 This makes them relatively stronger than most stream based ciphers
 Also makes them computationally intensive and expensive to implement
 Streambased ciphers are usually implemented in hardware and block ciphers are usually implemented in software
Encryption Systems
 Substitution ciphers
 Substitutes one letter for another based on cryptovariable
 Transposition ciphers
 Monoalphabetic and polyalphabetic ciphers
 Modular mathematics
 Represents each letter by the modulus of its numerical place in the alphabet modified by a key
 Running key cipher
 Key is repeated for the same length as the plaintext input
Encryption Systems
 Onetime Pads
 Steganography
 Hides a message inside another medium
 Watermarking
 Code words
Summary
Cryptographic concepts Portfolio Assignment
Topics in Computer Science
 Algorithm Assignment Help
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 Computer Networks
 Data Structures
 Discrete Mathematical Structures
 Help with Engineering Homework
 Operating Systems
 Analysis and Design of Algorithms
 Architecture of High Performance Computers
 Artificial Intelligence
 Compiler Design
 Digital Hardware Design
 Foundations of Automatic Verification
 Introduction to Database Systems
 Introduction to Logic and Functional Programming
 Logic for Computer Science
 Numerical and Scientific Computing
 Resource Management in Computer Systems
 Simulation and Modeling
 Software Engineering
 Synthesis of Digital Systems
 Theory of Computation
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