Submission for Task $1(20$ points$)$

$(1)$ Which ciphers you have tried? $(5$ points$)$

$(2)$ What are commands you used for those ciphers? Please write down $($you can copy and paste$)$ the

commands or attach a screenshot of your commands in your report. $(10$ points$)$

$(3)$ Can you successfully decrypt ciphertext which is encrypted by your selected ciphers? Please write down

one command you used to decrypt your ciphertext. $(5$ points$)$

$2$ Task $2$: Encryption Mode$-$ECB vs$.$ CBC

The file pic$\_$original.bmp can be downloaded from this lab's website, and it contains a simple picture. We

would like to encrypt this picture, so people without the encryption keys cannot know what is in the picture.

Please encrypt the file using the ECB $($Electronic Code Book$)$ and CBC $($Cipher Block Chaining$)$ modes,

and then do the following:

Let us treat the encrypted picture as a picture, and use a picture viewing software to display it$.$

However, For the $.$bmp file, the first $54$ bytes contain the header information about the picture, we

have to set it correctly, so the encrypted file can be treated as a legitimate $.bmp$ file. We will replace

the header of the encrypted picture with that of the original picture. We can use the bless hex editor

tool $($already installed on our VM$)$ to directly modify binary files. We can also use the following

commands to get the header from pl$.$bmp$,$ the data from $p2.bmp($from offset $55$ to the end of the

file$),$ and then combine the header and data together into a new file.

$ head $-$c $54$ p$1$ bmp $>$ header

$ tail $-$c $+55$ p$2.$bmp $>$ body

$ cat header body $>$ new.bmp

Display the encrypted picture using a picture viewing program $($we have installed an image viewer

program called eog on our VM$).$ Can you derive any useful information about the original picture

from the encrypted picture? Please explain your observations

Select a picture of your choice, repeat the experiment above, and report your observations.

Submission for Task $2(20$ points$)$

$(1)$ Please attach the screenshots of images which are encrypted using ECB and CBC modes respectively.

Please note that the encrypted images are the ciphertext and you may want to change the header

information before you can open the encrypted images. $(5$ points$)$

$(2)$ What is difference between the image encrypted using ECB mode and that encrypted using CBC mode.

Which mode is more secure$?$ And why? $(10$ points$)$

$(3)$ Please attach the picture of your choice, the encrypted picture using ECB and CBC modes. $(5$ points$)$