Chapter 7: One-Time Pad or “Vernam Cipher”:

• Invented by Gilbert Vernam in 1917, considered a perfect encryption scheme because it is considered unbreakable if implemented properly.
• This cipher uses a pad made up of random values, the plaintext message that needs to be encrypted get converted into bits, and the one-time pad is made up of random bits.
• The encryption process uses a binary mathematical function called exclusive-OR (XOR).
•  XOR is an operation that is applied to two bits and is a function commonly used in binary mathematics and encryption methods.
• When combining the bits, if both values are the same, the results is 0 ( 1 XOR 1 = 0), but if the bits are different from each other, the result is 1 (1 XOR 0 = 1).
•  Example:

                                    Message stream 1001010111

                                    Keystream 0011101010

                                    Ciphertext stream 1010111101

• For the one-time pad encryption scheme to be unbreakable the follow has to be true about the implementation process:
• The pad must be used only one time, if not it can introduce patterns.
• The pad must be as long as the message, if it’s not as long as the message the pad will be reused to cover the whole message and that would be the same as using the pad more than once.
• The pad must be securely distributed and protected as its destination, the pads are usually individual pieces of paper that need to be delivered by a secure courier and properly guarded at each destination.
• The pad must be made up of truly random values.

Chapter 7: Services of Cryptosystems:

• Cryptosystems provide the following services:
• Confidentiality: Renders the information unintelligible except by authorized entities.
• Integrity: Ensure that data has not been altered by an unauthorized manner since it was created, transmitted, or stored.
• Authentication: After identification has been proven, the individual is then provided with the key or password that will allow access to some resources.
• Nonrepudiation: Ensures the sender cannot deny sending the message. 

Chapter 7: The Strength of the Cryptosystem

• The algorithm, the secrecy of the key, the length of the key, the initialization vectors, and how they all work together within the cryptosystem provides the strength of an encryption method.
• Strength is how hard it is to figure out the algorithm or key and the goal on designing an encryption method is to make compromising it too expensive or time-consuming.
• Work factor is another name for cryptography strength and it estimates the effort and resources it would take an attacker to penetrate a cryptosystem.
• Important element of encryption are to use an algorithm without flaws, use a large key size, use all possible values within the keyspace, and protect the key and if one element is weak, it can be the causing factor for the process to fail. 

Chapter 7: Cryptography Definitions and Concepts:

• Encryption is a method for transforming readable data (plaintext), into a form that appears to be random and unreadable (ciphertext).
• Cryptosystem is a system or product that provides encryption and decryption and it created through hardware components or program code in an application.
• The cryptosystem uses an encryption algorithm (which determines how simple or complex the encryption process will be), keys, and the necessary software components and protocols.
•  Most encryption methods use a secret value called key, which is a long string of bits, and works together with the algorithm to encrypt and decrypt the text.
• A Cryptosystems is made up of at least the following:
•  Software
• Protocols
•  Algorithms
• Keys
• Algorithm is a set of rules also known as the cipher, dictates how enciphering and deciphering takes place.
• The Key (cryptovariable) is a value that can comprises a large sequence of random bits.
• The Keyspace is a range of values that can be used to construct a key.
• The larger the keyspace, the more available values can be used to represent different keys, this will provide for a more random set of keys and it will be harder for intruders to figure them out.

Kerckhoff’s Principle

Auguste Kerckhoff, published a paper in 1883

• States that only secrecy involved with cryptography systems should be the key and the algorithms should be publicly known.
• Argument:
• If an algorithm is publicly known more people can view the source code, test it, and uncover any type of flaws or weaknesses, then the developers can fix it.
• Government's Argument:
• If smaller number of people know how the algorithm actually works, then a smaller number of people will know how to possibly break it. 

 

Chapter 7: Cryptography

What is Cryptography?

• Cryptography is a method of storing and transmitting data in a form that only those it is intended for can read and process (Harris, 759).
• Cryptography is considered the science of protecting information by encoding it into a unreadable format.
• It is an effective way of protecting sensitive information because cryptography is stored in media or transmitted through entrusted network communication paths.
• The goal is to hide information from unauthorized individuals, but it is unattainable because with enough time, resources, and motivations hackers will break most algorithms and revel the encoded information.
• A realistic goal of Cryptography is to make obtaining information too work-intensive or time-consuming to be worthwhile to the attacker.

Chapter 6: Physical Layer

•  Layer 1
• Converts bits into voltage for transmission because signals and voltage schemes have different meanings for different LAN and WAN technologies.
• This layer controls synchronization, data rates, line noise, and transmission techniques.
• Specifications for the physical layer include that timing of voltage changes, voltage levels, and the physical connectors for electrical, optical, and mechanical transmissions.

Chapter 6: Data Link Layer

• Layer 2
• The data link layer is responsible for proper communication within the network components and for changing the data into the necessary format (electric voltage) for the physical layer.
• It is divided into two layers:
• Logical Link Control (LLC):
•  Communicate with the protocol immediately about it (network layer).
• Media Access Control (MAC)
• Have the appropriately loaded protocols to interface with the protocol requirements of the physical layer.