We consider a banking application, where messages m of the form fromAccount, toAccount, amount are sent within the bank network, with the meaning that amount dollars should be transferred from fromAccount to toAccount. Each message consists of three blocks, with each block holding one of the three parameters. Messages are encrypted using AES in Counter mode, i. e.Kj = E(K, Tj)Cj = Mj ⊕ KjEach of the three parts of a message is sixteen characters, i. e. one block, so messages consist of three blocks. a. The adversary has an account in the bank and can intercept and change messages. Imagine now that he knows the toAccount for a particular message m = C1C2C3. Explain how he can modify the message so that the amount is transferred to his own account. b. Explain how the use of a MAC would prevent this attack. c. Above, E(K, M) denotes using block cipher E with key K on message M. It is possible to define a cipher using similar ideas, but using a hash function instead. Describe how to do it, including how to decrypt.

You have a linux system that has a 1000gb hard disk drive, which has a 90gb partition containing an ext4 filesystem mounted to the / directory and a 4gb swap partition. currently, this linux system is only used by a few users for storing small files; however, the department manager wants to upgrade this system and use it to run a database application that will be used by 100 users. the database application and the associated data will take up over 200gb of hard disk space. in addition, these 100 users will store their personal files on the hard disk of the system. each user must have a maximum of 5gb of storage space. the department manager has made it very clear that this system must not exhibit any downtime as a result of hard disk errors. how much hard disk space will you require, and what partitions would you need to ensure that the system will perform as needed? where would these partitions be mounted? what quotas would you implement? what commands would you need to run and what entries to /etc/fstab would you need to create? justify your answers.

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