Assignment 1 FIT3031: nformation and Network Securit emester 2018 Con 4. Alice and Bob are employees of two different financial investment companies. Alice works for the S&M investment funds that operates in Melboueand Bob works for MK Superfunds that operates in Sydney. Alice and Bob are both familiar with modern cryptographic tools and know how to use the tools to perform symmetric and asymmetric encryption algorithms as well as generating hash and message authentication cocles. During a conference organisecl by both companies Alice aud Bob have met and exchanged their public keys. Using the provided notation for each of the following scenarios define a protocol that achieves the roquired goals. Notation: M is the message (file), H)a cryptographically strong hash function, E) an encryption algorithm corresponding to the specified keys (symmetric for secret key, asymmetric for public/private key), MACs a Message Authentication Code algorithm, Kxy is a secret key shared between entities X and Y (symmetrie algorithm), PUx is the public key and PRx the private key of entity X (asymmetric algorithm), is concatenation function, X Y specities X sends to Y For each of the scenarios that follows the example you need to: define the protocol in one linusing the provided notation; . and then explain clearly why it satisfies the requirements of the given soenario (for instance why an attacker will not sceed and how recever can verify whether the required property is achieved) Example: Alice must send a message over a public network to Bob where only the confidentiality of the message is required and Alice and Bob have already a shared secret KAB Protocol: A -+B :E(KAB,M) Explanation: Since Alie and B have already a shared set KAB Alice can usea ymmetric cncryption algorithm to transform the mcssage to ciphertext. To rocover the original plaintext message the kowledge of the secret key is required hece an attacker such a Eve who does not kuow the value of t!shared secret kev KAB cannot recover the original message rom the captured ciphertext. Bob can recover the message using the decryption algorithm and the sharod secret Notes When the scenario asks for efficiency it es you will receive no or partial mark if your proposed protocol is not the most efficient approach that satisfies the requirements. of Kxr, PUx, and PRx respectively (to simplify the use of your chosen word processor) represents the message and the hash of the message. E(KAB,MM) are two different protocols possibly providing different services . You can also use 1,->" in place of , and "K XV", X", and "PR X" notations in place Us concatcnation || when the protocol is compriscd of multiple parts, for cxample MlH(M) . Use brackets to specify the scope of a function. for example E (KAB, M) H(M) and . You can use both symmetric and asymmetric algorithms in the sae protocol when necessary. Scenarios: Alice needs to send a lGB (GigaByte) file to Bob over a public network. (a) Explain how Alice could efficiently send the file when it contains public information that must not be tampered with and Bob must know Alice is the only entity who could have sent the file. (b) Explain how Alice could efficiently send the file when it contains confidential information and Bob must know Alice is the only entity who could have sent the file, if Alice and Bob already have a shared secret (c) Explain how Alice could efficiently send the file that needs to be confidential to Bob when they have not a shared secret (d) Explain how Alice could efficiently send the file when it contains public information that inust not be anpered with (only integrily is important) and Alice nd Bb already have a shared sccret. 24 Marks]
