13-06-2012, 11:48 AM
CRYPTOGRAPHY
Cryptography_and_Network_Security_9.doc (Size: 210.5 KB / Downloads: 32)
Abstract
Cryptography is science of writing secret code of using mathematics to encrypt and decrypt data. Cryptography enables to store sensitive information or transmit it across insecure networks (like the Internet) so that it cannot read by anyone except the intended recipient.
Cryptography is a complicated subject, historically only tackled by well-trained and experienced experts. However, as more and more people become ``wired'', an increasing number of people need to understand the basics of security in a networked world, explaining the concepts needed to read through the hype in the marketplace and understand risks and how to deal with them. We go on to consider risk management, network threats, firewalls, and more special-purpose secure networking devices.
The networks are both public and private, that are used every day to conduct transactions and communications among businesses, government agencies and individuals. The networks are comprised of ‘nodes’, which are ‘client’ terminals, and one or more ‘servers’ and ‘host’ computers. They are linked by communication systems, some of which might be private, such as within a company and others which might be open to public access. The obvious example of a network system that is open to public access is the Internet, but many private networks also utilize publicly-accessible communications. Today, most companies' host computers can be accessed by their employees whether in their offices over a private communications network, or from their homes or hotel rooms while on the road through normal telephone lines.
What is a Network? : A ‘network' has been defined as ‘any set of interlinking lines resembling a net, a network of roads an interconnected system, a network of alliances.’ A computer network is simply a system of interconnected computers. How they're connected is irrelevant, there are a number of ways to do this.
What is Cryptography? : Cryptography is the study of mathematical techniques related to aspects of information security such as confidentiality, data integrity, entity authentication, and data origin authentication. Cryptography is not the only means of providing information security, but rather one set of techniques. One essential aspect for secure communications is that of cryptography, Network security Measures Company to protects computer systems, and it’s prime concern for every company that uses computers. Compromised network security means a hacker or competitor may gain access to critical or sensitive data, possibly resulting in data loss, or even complete destruction of the system. Appropriate network security is achieved when a user has to go through several layers of security before being able to access the desired network. ‘The more layers the system has, the more secure it is’. The systems administrator is often in charge of network security since he has administrator privileges on the system. A systems administrator will also build a secure firewall for the network, which may include an encryption layer and sentinel. Software’s that automatically repels an unauthorized programmers from gaining access, The administrator may also place restrictions on employees’ computers to prevent them from accessing websites that may have malicious coding or malware that will install itself on a user’s computer. U.S. companies spend millions of dollars each year in network security measures. Firewalls with no single point of access, sharp system administrators, frequent security updates, and early installation of anti-adware will all help keep a network safe.Network security involves all activities that organizations, enterprises, and institutions undertake to protect the value and ongoing usability of assets and the integrity and continuity of operations. An effective network security strategy requires identifying threats and then choosing the most effective set of tools to combat them.
The purpose of cryptography: Cryptography is the science of writing in secret code and is an ancient art; the first documented use of cryptography in writing dates back to circa 1900 B.C. when an Egyptian scribe used non-standard hieroglyphs in an inscription. Some experts argue that cryptography appeared spontaneously sometime after writing was invented, with applications ranging from diplomatic missives to war-time battle plans. It is no surprise, then, that new forms of cryptography came soon after the widespread development of computer communications. In data and telecommunications, cryptography is necessary when communicating over any entrusted medium, which includes just about any network, particularly the Internet. Within the context of any application-to-application communication, there are some specific security requirements, including:
Authentication: The process of proving one's identity. (The primary forms of host-to-host authentication on the Internet today are name-based or address-based, both of which are notoriously weak.)
Privacy/confidentiality: Ensuring that no one can read the message except the intended receiver.
0 Integrity: Assuring the receiver that the received message has not been altered in any way from the original.
0 Non-repudiation: A mechanism to prove that the sender really sent this message.
Cryptography, then, not only protects data from theft or alteration, but can also be used for user authentication. There are, in general, three types of cryptographic schemes typically used to accomplish these goals: secret key (or symmetric) cryptography, public-key (or asymmetric) cryptography, and hash functions, each of which is described below. In all cases, the initial unencrypted data is referred to as ‘plaintext’. It is encrypted into ‘cipher text’, which will in turn (usually) be decrypted into usable plaintext.
Types of cryptographic algorithms: There are several ways of classifying cryptographic algorithms. This will be categorized based on the number of keys that are employed for encryption and decryption, and further defined by their application and use.
Secret Key Cryptography (SKC): Uses a single key for both encryption and decryption
0 Public Key Cryptography (PKC): Uses one key for encryption and another for decryption
0 Hash Functions: Uses a mathematical transformation to irreversibly "encrypt" information
Secret Key Cryptography(SKC): With secret key cryptography, a single key is used for both encryption and decryption, the sender uses the key (or some set of rules) to encrypt the plaintext and sends the cipher text to the receiver. The receiver applies the same key (or rule set) to decrypt the message and recover the plaintext. Because a single key is used for both functions, secret key cryptography is also called ‘symmetric encryption’.
With this form of cryptography, it is obvious that the key must be known to both the sender and the receiver; that, in fact, is the secret. The biggest difficulty with this approach, of course, is the distribution of the key. SKC schemes are generally categorized as being either ‘stream ciphers’ or ‘block ciphers’.
Cryptanalysis attack: There are two types of cryptanalysis.
Ordinary Cryptanalysis: This can be done by knowing the characteristics of algorithms, trying to convert plaint text to cipher text
0 Brute force Cryptanalysis: This can be done by without knowing the characteristics of algorithms, trying the possible ways to convert plaint text to cipher text
Encryption techniques: There are two types. One is Substitution , other transposition.
Substitution ciphers: substitution ciphers are block ciphers which replaces symbols (or group of symbols) by other symbols. Types of substitution ciphers are:
0 Caeser cipher: It was developed by Julius caeser. In this cipher each char of the plaintext is replaced by the character that stand ‘key shift’ (for ex: n=3) further down the alphabet
0 Play fair cipher: It was first developed by ‘Ben Charles’ in1854, this cipher encrypt the plaintext in the form of table by using any of the keywords like ‘MONARCHY’ etc...
0 Hill cipher: It was developed by ‘Lester hill’ in 1929, Here ‘m’ characters of plain text encrypted to ‘m’ characters of cipher text using the help of ‘m’ linear equations.