ccna audiobook

ccna audiobook.In a symmetric key system, both communicating parties must have the same key. Securely exchanging these keys has always been a challenge. Asymmetric key systems solve this challenge because they use two keys. One key is known as the private key and the other key is known as the public key. The private key is confidential and known only to the user. The public key is shared publicly and is easy to distribute.DH is a mathematical algorithm that allows two computers to generate the same shared key on two systems without prior communication. The new shared key is not really exchanged between the sender and the receiver. But because both parties know this key, the encryption algorithm can use it to encrypt traffic between the two systems. Its security is based on the fact that when a number is very large, one has difficulty calculating its discrete logarithm.DH is often used when exchanging data using IPSecVPN (data is encrypted over the Internet using SSL or TLS) or when exchanging SSH data. Unfortunately, for any kind of bulk encryption, asymmetric key systems are extremely slow. This is often the case with DES, 3DES7.3 Confidentiality 205 or symmetric algorithms like AES to encrypt bulk traffic and use the DH algorithm to generate the keys used by the encryption algorithm.7.3.6.2 DH OperationTo help understand how DH is used, consider the example of communication between Alice and Bob. The DH process consists of 6 steps. To begin the DH exchange, Alice and Bob must agree on two unclassified numbers. The first number, g, is the base number (also called the generator). The second number, p, is a prime number used as a modulus. These numbers are usually public and are chosen from a table of known values. Typically, g is a very small number, such as 2, 3, 4, or 5, and p is a larger prime number. Next, Alice generates a secret number Xa and Bob generates his secret number Xb.Based on the small p and Alice's number X, Alice uses the DH algorithm to compute a public value (Ya). She sends her public value (Ya) to Bob.Bob also computes an overt value (Yb) using g, p and his secret number. bob sends his overt value (Yb) to Aliceo These values are not the same.