03-12-2012, 05:19 PM
CRYPTOGRAPHY
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INTRODUCTION
Cryptography is one of the humanity’s oldest professions having a history of more than 4000 years.Ancient people enciphered their writings on monuments,scriptures e.t.c.2000 years ago Julius Caesar used a simple substitution Cipher known as Caesar Cipher.
Classes of Algorithms:
There are 2 classes of Algorithms:
Key based Algorithms
Hashing Algorithms
There are two classes of key-based encryption algorithms:
Symmetric (or secret-key)
Asymmetric (or public-key) algorithms
Symmetric algorithms use the same key for encryption and decryption (or the decryption key is easily derived from the encryption key)
Asymmetric algorithms use a different key for encryption and decryption, and the decryption key cannot be derived from the encryption key.
Practical Use Of RSA:
RSA is currently used in a wide variety of products, platforms,
and industries around the world. It is found in many commercial
software products and is planned to be in many more. It is built
into current operating systems by Microsoft, Apple, Sun, and
Novell. In hardware, RSA can be found in secure telephones, on
Ethernet network cards, and on smart cards. In addition, RSA is
incorporated into all of the major protocols for secure Internet
Man-in-the-middle attack:
This attack is relevant for cryptographic communication and key exchange
protocols. The idea is that when two parties, A and B, are exchanging keys for secure communication (e.g., using Diffie-Hellman), an adversary positions himself between A and B on the communication line. The adversary then intercepts the signals that A and B send to each other, and performs a key exchange with A and B separately. A and B will end up using a different key, each of which is known to the adversary.
Types of algorithms
Public Key
Good cryptographic systems should always be designed so that they are as difficult to break as possible. It is possible to build systems that cannot be broken in practice (though this cannot usually be proved). This does not significantly increase system implementation effort; however, some care and expertise is required.
Modern cryptographic algorithms are no longer pencil-and-paper ciphers. Strong cryptographic algorithms are designed to be executed by computers or specialized hardware devices. In most applications, cryptography is done in computer software.