Getting Ready for Chapter 4 - Answers
1. Hashes are used in security systems to ensure that transmitted messages have not been tampered with.
Explanation: Hashes play a role in security systems where they're used to ensure that transmitted messages have not been tampered with. The sender generates a hash of the message, encrypts it, and sends it with the message itself. The recipient then decrypts both the message and the hash, produces another hash from the received message, and compares the two hashes. If they're the same, there is a very high probability that the message was transmitted intact.
2. Two widely used applications of cryptography are identification and authentication .
Explanation: Identification and authentication are two widely used applications of cryptography. Identification is the process of verifying someone's or some thing's identity. For example, when withdrawing money from a bank, a teller asks to see identification (e.g. a driver's license) to verify the identity of the owner of the account. This same process can be done electronically using cryptography. Every automatic teller machine (ATM) card is associated with a "secret" personal identification number (PIN), which binds the owner to the card and thus to the account. When the card is inserted into the ATM, the machine prompts the cardholder for the PIN. If the correct PIN is entered, the machine identifies that person as the rightful owner and grants access.
3. The main role of a cryptographic hash function is in the provision of message integrity checks and digital signatures .
Explanation: The main role of a cryptographic hash function is in the provision of message integrity checks and digital signatures. Since hash functions are generally faster than encryption or digital signature algorithms, it is typical to compute the digital signature or integrity check to some document by applying cryptographic processing to the document's hash value, which is small compared to the document itself.
4. A digital digest can be made public without revealing the contents of the original document?
Explanation: A digest can be made public without revealing the contents of the document from which it is derived. This is important in digital time stamping where, using hash functions, one can get a document time stamped without revealing its contents to the time stamping service.
5. A certificate is used to allow verification of the claim that a specific public key does in fact belong to a specific individual.
Explanation: Certificates are issued by the certificate authority. Certificates are digital documents attesting to the binding of a public key to an individual or other entity. They allow verification of the claim that a specific public key does in fact belong to a specific individual. Certificates help prevent someone from using a phony key to impersonate someone else. In some cases it may be necessary to create a chain of certificates, each one certifying the previous one until the parties involved are confident in the identity in question.
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