ccna age

ccna age.7.2.1.1 The cryptographic hash function7.2 Basic Integrity and Authenticity 193Hashing is used to ensure the integrity of data. The hash function accepts binary data (called a message) and generates a compressed representation of a fixed length (called a hash). The final generated hash sometimes becomes a message digest or fingerprint (fingerprint) o Hashing is based on a one-way mathematical function that is relatively easy to compute but very difficult to reverse. Grinding coffee is a good example of a one-way function. It is easy to grind the coffee beans, but it is almost impossible to restore all the small pieces to the original coffee beans. The purpose of designing a cryptographic hash function is to verify and ensure data integrity. It can also be used to verify identity. This process takes a variable block of data and returns a fixed-length string of bits called a hash value or message digest.Hashing is similar to computing the checksum of a cyclicredundancycheck (CRC), but it is much stronger encryption. For example, given a CRC value, it is easy to generate data using the same CRC. Using the hash function, it is computationally infeasible to get the same hash output for two different sets of data. Each time the data changes or is altered, the hash value also changes. For this reason, cryptographic hash values are often referred to as digital fingerprints, and they can be used to detect duplicate data files, file version changes, and similar applications. These values are used to guard against unintentional or intentional changes to data as well as accidental data corruption.Cryptographic hash functions are used in many different situations.When used with symmetric secret authentication keys (such as IPSec or routing protocol authentication), to provide evidence of authenticity.Provides authentication by generating a one-time one-way response to a challenge in an authentication protocol such as PPP Challenge Handshake Authentication Protocol (CHAP). o Provide message integrity check evidence (e.g., those used in digitally signed contracts) and PublicKey Infrastructure (PKI) certificates (e.g., those accepted when using a browser to access a secure site).7.2.1.2 Characteristics of Cryptographic Hash Functions (property )Mathematically, a hash function (H) is a process that takes an input (x) and returns a fixed-length string called the hash value (*). The formula is h = H(x). A cryptographic hash function should have the following characteristics. The input can be of arbitrary length. The output is of fixed length.