A-LevelComputer ScienceSecurity, privacy and data integrity9618/31 · May/June 2022 · Q88 Marks

A message is to be sent securely. Software uses a key to encrypt the message before it is sent.

(a)(i)Give two reasons for using key cryptography. 1 2[2]
(a)(ii)Give two methods of key cryptography that can be used. 1 2[2]
(b)(i)When there is a secure exchange of key(s), the message is sent. The use of quantum cryptography is being considered for the secure exchange. State two possible benefits of using quantum cryptography. 1 2[2]
(b)(ii)State two possible drawbacks of using quantum cryptography. 1 2[2]

Mark scheme

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

[2] 8(a)(i) Any two from • To ensure the message is authentic // came from a trusted source • To ensure that only the intended receiver is able to understand the message • To ensure the message has not been altered during transmission • Non-repudiation, neither the sender or receiver can deny the transmission occurred
[2] 8(a)(ii) Symmetric Asymmetric
[2] 8(b)(i) Any two from • Any eavesdropping can be identified (as the state will be changed) • Integrity of the key once transferred can be guaranteed (cannot be copied and decrypted at a later date) • Longer/more secure keys can be exchanged
[2] 8(b)(ii) Any two from • Limited range • requires dedicated fibre (optic) line and specialist hardware • cost of dedicated fibre (optic) line and specialist hardware is expensive • polarisation of light may be altered whilst travelling down fibre optic cables

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