Please finish and answer my lab questions

CIS 4378 Introduction to Computer and Network Security

Lab 4

Objective: Experiment with symmetric key encryption.

Submission: Please email solutions by 10/02/2017, 5pm, using the Canvas system.

1. In this lab, we will use the openssl and GHex programs. Ensure that the programs are correctly

installed on your virtual machine by running the following commands:

cct@cct-vm:$ dpkg –s openssl

cct@cct-vm:$ dpkg –s ghex

If you wish to update the software installed on your VM to the latest version, you may do so with

the following command (Note - you will be prompted for the cct user password to obtain elevated

privileges for the software update):

cct@cct-vm:$ sudo apt-get update

If the programs are NOT installed on your VM, you may install them with the following commands:

cct@cct-vm:$ sudo apt-get install openssl

cct@cct-vm:$ sudo apt-get install ghex

2. We will first experiment with openssl. All commands will be entered in the terminal. To get more information about openssl command, type “man openssl”.

3. To encrypt or decrypt a file, refer the following sample commands where ciphertype, in-

file, out-file, key and iv_used are replaced with the appropriate values. (“>>” indicates a

command to be executed; do not actually type “>>” into the terminal.) Note the differences

between encrypting with the “-e” flag, and decrypting with the “-d” flag.

>> openssl enc ciphertype -e -in in-file -out out-file -K key -iv iv_used

>> openssl enc ciphertype -d -in in-file -out out-file -K key -iv iv_used

4. We first see the options when we are encrypting a file. Execute the example encryption command

listed above, substituting in the following values for the respective parameters. Check with the TA if

you are unsure if you are doing it correctly.

• ciphertype: -aes-128-cbc

• in-file: text.txt (create your own file with a few of lines of text)

• out-file: cipher.bin (no need to do anything; will be created automatically)

• key: 12345

• iv_used: 0123

Question 1. Copy the contents of the text.txt and cipher.bin into your report. Can you see any

relationship between the two files?

Question 2. Now try creating different versions of text.txt, e.g. minor differences, very different,

different characters, etc.. What can you see about the relationship between these different cipertext?

5. Now we will decrypt the file you encrypted earlier. We will use the following parameters. Make

sure you can get back what you encrypted.

• ciphertext: -aes-128-cbc

• in-file: cipher.bin

• out-file: answer.txt (named something different from text.txt so as to compare)

• key: 12345

• iv_used: 0123

Question 3. Attempt to decrypt the cipher.bin using a different iv_used value. What happens to

the plain text you get back? Try with different iv_used values and present the results in your

report.

Question 4. What happens when you attempt to decrypt a file using the correct key and iv value,

but using a different encryption mode, such as –aes-128-ecb, –aes-256-cbc, and/or –dec-cbc?