Chapter 7: Cryptography - Types of Asymmetric Systems

Just having symmetric key cryptography has many drawbacks. This is why asymmetric systems were developed. The first one developed is called the Diffie-Hellman Algorithm. Here, two different systems can make a symmetric key in a secure manner without first having established a relationship or agreement. It is however, vulnerable to man-in-the-middle attacks. Another asymmetric algorithm, RSA, is the standard used for digital signatures. It provides key encryption and is secure because it factors large numbers into their prime numbers. A third is El Gamal, which is an extension of Diffie-Hellman. It works by calculating discrete logs in a finite field. It is usually the slowest form.

Chapter 7: Cryptography - Types of Symmetric Systems

Data Encryption Standard (DES) - Algorithm is block symmetric. 56-bit true key bit. Block size is 64-bit. Has 16 rounds of computation.

3DES (Triple DES) - When encryption occurs, applies DES three times to each block of data.

Blowfish - Block size is 64-bit and keys can vary in length. Anyone can use it.

Rijndael - Chosen for AES. Block size is 128-bit and different key lengths are used (either 128 bits, 192 bits, or 256 bits).

International Data Encryption Algorithm (IDEA) - Block size is 64-bit and uses a 128-but key.

RC4 - This is a stream cipher. Key size can change. Simple, fast, but an easy target for attackers.

RC5 - Block cipher whose block sizes can be 32-bits, 64-bits, or 128-bits.Key has a limit of 2048-bits.Round limit is 255.

RC6 - Built upon RC5 and is the same for the most part. However, it is quicker than RC5.

Advanced Encryption Standard (AES) - Standard in the United States that replaced DES. 128 block size and key lengths vary from 128, 192, and 256.

Secure ans Fast Encryption Routine (SAFER) - Similar to DES but harder to break because of the size of the key is bigger. No known successful attacks as of now. It is also patented, so you have to pay to use it.

Chapter 7: Cryptography - Ciphers and Encryption Methods

There are two types of ciphers.

1. Substitution cipher - replaces characters with different characters.
2. Transposition cipher - Moves the values around. Does not replace values but hides the original meaning.

There are also two types of algorithms that are associated with cryptography:

1. Symmetric - user and sender use two instances of same key for encryption and decryption. Also known as secret keys. Equation to determine number of keys needed: N(N -1)/2. This method is a lot faster but must have secure mechanism to deliver keys the right way.

2. Asymmetric - each entity has different keys and are the two are related mathematically. For example, if one is used to encrypt the other must be used to decrypt. Public key is known to everyone, and only the owner uses the private key. There is better key distribution here, but is is much slower than the symmetric way.

Ofter good practice to use symmetric algorithms and asymmetric algorithms together. This is known as Hybrid Encryption.

Chapter 7: Cryptography - Cryptography Definitions and Concepts

Plaintext is the term used for readable data, whereas ciphertext is the data in its encrypted state. It is important to note that neither humans or machines should be able to properly read the data in its encrypted state. Only when the data is decrypted should it be able to be read by either human or machine. So, the process goes like this: plaintext is encrypted, and it becomes ciphertext. Then, in order to be read, the ciphertext is decrypted and becomes plaintext once again in order to read and used. Algorithms, a set of rules, are used to encrypt and decrypt data. A crptosystem is all of the things that make up an encryption and decryption process and should always be made up of software, protocols, algorithms, and keys. A key or crypto variable, is a single value that makes up a sequence of bits that are random. The algorithm that does the encryption and decryption should always be known, and only the keys should be kept secret. Bigger keyspaces allow for more possible keys, strengthening the encryption method. The one-time pad scheme is considered to be unbreakable if used in the right way. To work correctly, it must be constructed with truly random values, only used once, distributed securely, secured by the sender and the recipient, and must be as long as the message. This is a very basic description of how encryption works, and it does get more complicated than this.

Chapter 7: Cryptography - History of Cryptography

The first known use of cryptography can be dated back to 2000 B.C. in ancient Egypt. One of the earliest applications of cryptography was a hebrew method that replaced each letter of the alphabet with a different letter. We now have a term for this, and it is known as substitution cypher. Here is an example of this, with the letter 'A' being replaced with 'Z', 'B' being replaced with 'Y' and so on. So the word 'CRYPTOGRAPHY' would become 'XIBKGLTIZKSB'.  This is also known as a monoalphabetic substitution cypher because only one alphabet is used. If more than alphabet is used, it is then referred to as polyalphabetic. As time moved forward, algorithms were developed to improve methods of encryption. Today, there is the science of cryptanalysis, in which breaking down encryption is studied as well as reverse engineering the algorithms that encrypt data.

Chapter 6: Telecommunications and Network Security - OSI Layers

OSI stands for Open Systems Interconnection. There are various functions and protocols of the OSI model and the study guide states that if you want to take the exam, you will need be be pretty familiar with these.

Application - in charge of file transfer, network management, and fulfilling network requests. My favorite protocol example here is HTTP, because I am familiar with it and understand how it works for the most part.

Presentation - Handles data formats, and encryption. ASCII is one standard that is concerned with the presentation aspect of OSI.

Session - This layer sets up the connection of applications. A good protocol example here is SQL.

Transport - This is like an agreement between two computers. How much stuff will be sent is a concern, as well as how the receiving end will verify and handle the data.

Network -Main responsibility here is to tell the packet where it needs to go, and to get it to its correct destination. An IP address is a good example for this one.

Data Link - Changes the data into LAN or WAN frames for transfer and sets up how a computer will gain access to a network. Ethernet is one protocol that is associated with this layer.

Physical - The conversion of bits to actual electrical signals for transmission. A familiar term that you is in use here would be a digital subscriber line (DSL).

http://compnetworking.about.com/od/basicnetworkingconcepts/l/blbasics_osimod.htm

Chapter 6: Telecommunications and Network Security - Intro

At our day in age, networking has become increasingly complex. A network used to have boundaries, but now, since we basically have a computer in our pocket that is capable of networking, there is no clear cut boundary of individual networks. As technology increases, so do threats from attackers. Because of this, the security professionals of today must understand networks on various levels. Telecommunications is the transmission of data through systems. The data can be carried through cables, or it can be wireless. There are two main organizations that govern telecommunications. The International Telecommunications Union (ITU) and the International Standards Organization (ISO).