ccna after

ccna after.7.1.1.2 AuthenticationIn network communication, there are two main methods that can be used to authenticate the source of a message: the authentication service and the data nonrepudiation service. oAuthentication ensures that a message comes from the source it claims to come from. Authentication is similar to entering a secure PersonalInformationNumber (PIN) when banking at an ATM, which is known only to the user and the financial institution.The PIN is a shared password used to prevent forgery. In network communication, authentication can be achieved using cryptographic methods. This is particularly important for applications (e.g., email) or protocols (e.g., IP) that do not have built-in mechanisms to prevent source spoofing.Data recognition is a similar service that allows the sender of a message to be uniquely identified. Using an acknowledgement service, the sender cannot deny that it is the source of the message. Although it appears that authentication and recognition services perform the same function, and although both address the problem of confirming the identity of the sender, there are differences between them.The most important part of data recognition is that a device cannot deny or disprove the validity of the message sent. Endorsement relies on the fact that only the sender has unique characteristics and features that can be used in the processing of that message. Even the receiving device cannot know how the sender processes the message to confirm its authenticity, otherwise the receiver would be able to disguise itself as the source.If the main concern is to have the receiving device verify the legitimacy of the source, and not to have the receiving device pretend to be the source, it is irrelevant whether both the sender and the receiver know how to process the message to provide authenticity. An example where authenticity is contrasted with recognition is the exchange of data between two computers in the same company and the exchange of data between a customer and an e-commerce Web site. It is not necessary for two computers exchanging data within the same organization to prove which of them sent a message; the only thing that must be proved is that any message received by one was sent by the other. In this example, the two computers can share the way in which the message format is converted.This practice would be unacceptable in a commercial application (e.g., buying goods online through an online store). If the webstore knows how the customer converts the message format to prove the authenticity of the source, the webstore can easily forge the "real" order. In this scenario, the sender must be the only party that knows how to convert the message format. The webstore can prove to others that the order was actually sent by the customer, and the customer cannot disprove that the order is invalid.7.1.1.3 Data IntegrityData integrity ensures that messages are not altered during transmission. With data integrity, the recipient is able to verify that the message received is the same as the message sent and has not been tampered with.European nobles use a wax seal to seal envelopes to ensure the data integrity of documents. The wax seal was usually created using . s to create the wax seal, which bore the family crest, initials, a portrait, or the personal mark or motto of the owner of the seal ring. The unbroken wax seal on the envelope ensures the integrity of the letter's contents, and the unique stamped seal of the seal ring ensures its authenticity.