A-LevelComputer ScienceCommunication and internet technologies9618/12 · Oct/Nov 2022 · Q69 Marks

A student uses a networked laptop computer to send an email to a colleague. The student records a sound file.

(a)(i)Explain how a digital signature ensures the email is authentic.[2]
(a)(ii)Describe how a firewall protects the data on the computer.[3]
(b)(i)Explain the effect of increasing the sampling rate on the accuracy of the sound recording.[2]
(b)(ii)Explain the effect of decreasing the sampling resolution on the file size of the sound recording.[2]

Mark scheme

Marking points from the official mark scheme (Oct/Nov 2022). The mark or mark type is shown in brackets.

[1] (email) message put through hashing algorithm to produce a digest
[1] Digest encrypted with sender's private key (to create the digital signature)
[1] the (digital) signature can only be decrypted with matching sender's public key
[1] monitors incoming and outgoing packets / traffic
[1] checks against an allow list / deny list of IP addresses // checks against a set of rules for acceptable data / ports etc.
[1] blocks transmissions that do not meet criteria / rules // allows through is satisfies the criteria /rules
[1] improves the accuracy of the sound file
[1] because (digital) waveform more closely resembles the analogue waveform
[1] quantization errors are reduced
[1] increases the amount of detail stored
[1] decreases the file size of the sound file
[1] because fewer bits are used to store each sample

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