Diffie And Hellman

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Introduction
Cryptography can be defined as the process of encrypting and decrypting data in order to keep the information protected from anyone other than the two (or more) people involved in the communication. Preventing unauthorized users from being able to read the information exchanged over an insecure channel, i.e. maintaining ‘privacy’ is one serious cryptographic problem, which is why it is essential for the communicating parties to share a key that is unknown to others. This key distribution problem levies major cost and delay to large business and/or teleprocessing networks.
Diffie and Hellman propose two ways to deal with transmitting keys over an insecure public channel without negotiating the security of the system:
1. Public
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Merkle suggested a system where two users A & B, securely exchange a key, over an insecure channel, and the same key is to be used for encryption and decryption of a message. Merkle’s protocol requires that ‘n’ potential keys be transmitted before one can be decided on, but this transmission overhead prevents the system from being very useful in practice.
Diffie and Hellman suggest another public key distribution system which require that just a single key be exchanged which can be tied to the public file of user. Also, the cryptanalytic exertion bears to develop exponentially.
The single key can be tied to the public file of the user, which serves to authenticate user A to user B and vice versa. This file is made a read memory, where one personal appearance permits a user to authenticate his identity several times to several users. Merkle’s technique requires A and B to verify each other’s activities by other means.
This method suggested by Diffie and Hellman makes use of the difficulty of computing logarithms over a finite field GF(q) with q number of elements, as its strength, or possibly adds to its computational
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This connection guarantees that all data exchanged between webservers and browsers are private and integral. The server owns a certificate with a DH public key in it. “https:” in the URL specifies that the encryption is taking place (‘s’ stands for secure) SSL was renamed TLS (Transport Layer Security) by the Internet Engineering Task Force (IETP) in 1999. The SSL/TLS consists of two layers. The lower layer referred to as the Record Protocol manages symmetric cryptography to ensure that communication remains private and reliable. The upper layer also known as the Handshake Protocol, is responsible for authentication of communicating parties and negotiation of encryption methods and keys used. This is where Diffie-Hellman is used. Earlier, the client and server exchanged unencrypted handshake messages. Now, the key exchange process uses public key cryptography to authenticate the user, done using session key pairs that are renewed over short time intervals for each session. After this exchange, secrets and keys are computed and the parties begin encrypting all the traffic between them, using the session key that was agreed

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