PLS NO PLAGIARISM

1. Guidance on key lengths changes over time.

(a) Name two reputable sources for key length recommendations (other than the ECRYPT recommendations of Table 10.1) and explain why they are credible sources.

(b) Towhatextentdotheirrecommendationsforsymmetrickeylengthsmatch the recommendations shown in Table 10.1?

(c) Given a public-key cryptosystem, explain how experts might determine which key length for this algorithm is equivalent to a symmetric key length of 128 bits.

2. Key backup is an important part of the cryptographic key lifecycle.

(a) Why is it important to back up cryptographic keys?

(b) In what ways might backup of cryptographic keys differ from backup of more general data on a computer system?

(c) As system administrator of a small organisation deploying symmetric cryptography for protection of all traffic on the local intranet, suggest what techniques and procedures you will use for the backup (and subsequent management of backed-up) cryptographic keys.

3. In the past, the idea of mandatory key escrow in order to facilitate access to decryption keys during an authorised government investigation has been proposed. (a) Explain what is meant by mandatory key escrow.

(b) What are the main problems with attempting to support mandatory key escrow within a key management system?

(c) An alternative approach is to provide a legal framework within which targets of an authorised investigation are forced by law to reveal relevant decryption keys. What are the potential advantages and disadvantages of this approach? (d) For the jurisdiction in which you currently reside, find out what (if any) mechanisms exist for supporting an authorised government investigation in the event that the investigators require access to data that has been encrypted.