AES Our friend Claude Shannon advocated for enciphering algorithms that did diffusion (spreading the effects of plaintext bits throughout the ciphertext) and confusion (spreading the effects of password bits throughout the ciphertext) In this question we will measure both effects, and a third Go to a Unix computer If you have a Mac or Linux, then get to the command line If you have a Microsoft OS machine, then putty into on of the following machines 140 192 36 185 140 192 36 186 140 192 36 187 using your Campus Connect username and password Make two files by doing typing this $ cat message0 txt This is 0 (Then press Enter and Ctrl D) $ cat message1 txt This is 1 (Then press Enter and Ctrl D) Diffusion Encipher them both with the password hello $ gpg symmetric a cipher algo AES256 message0 txt $ gpg symmetric a cipher algo AES256 message1 txt symmetric means use a symmetric cipher algorithm (as opposed to public key) a means make the output ASCII (as opposed to binary) This way we can easily see it cipher algo AES256 means use the 256 bit AES algorithm The output should be a file that looks something like BEGIN PGP MESSAGE Version GnuPG v2 0 22 (GNU Linux) jA0ECQMCkyoAgBGGEaHk0koBuO9eFQZtbALsAO49ovP0cNdcqQ370gyPePz SZeE BuUTAQs9yMTNIPzQlXE0 zjtjmoHQBWAJ fz5zTKWouLA5JLX2gRJQMJMQ 7TNS END PGP MESSAGE Note that there is only a 1 bit difference between both files '0' 0x30 0011,0000b '1' 0x31 0011,0001b Write a program to figure how many bits differ and how many bits stayed the same between message0 txt asc and message1 txt asc How many bits stay the same and how many differ Confusion You have enciphered message0 txt with the password hello Now encipher it with the password jello Note that there is only a 1 bit difference between both passwords 'h' 0x68 0110,1000b 'j' 0x6A 0110,1010b How many bits stay the same and how many differ (Partial) Defense against replay attacks Now, re encipher message0 txt with the password hello again Exact same file, exact same password How many bits stay the same and how many differ

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AES Our friend Claude Shannon advocated for enciphering algorithms that did diffusion (spreading the effects of plaintext bits throughout the ciphertext) and confusion (spreading the

AES

Our friend Claude Shannon advocated for enciphering algorithms that did diffusion (spreading the effects of plaintext bits throughout the ciphertext) and confusion (spreading the effects of password bits throughout the ciphertext). In this question we will measure both effects, and a third.

Go to a Unix computer. If you have a Mac or Linux, then get to the command line. If you have a Microsoft OS machine, then putty into on of the following machines:
- 140.192.36.185
- 140.192.36.186
- 140.192.36.187
using your Campus Connect username and password.

Make two files by doing typing this:

$ cat > message0.txt This is 0. (Then press Enter and Ctrl-D) $ cat > message1.txt This is 1. (Then press Enter and Ctrl-D)

Diffusion:

Encipher them both with the password hello:
```
$ gpg --symmetric -a --cipher-algo AES256 message0.txt $ gpg --symmetric -a --cipher-algo AES256 message1.txt 
```
- --symmetric means use a symmetric cipher algorithm (as opposed to public-key)
- -a means make the output ASCII (as opposed to binary). This way we can easily see it.
- --cipher-algo AES256 means use the 256-bit AES algorithm
The output should be a file that looks something like:
```
-----BEGIN PGP MESSAGE----- Version: GnuPG v2.0.22 (GNU/Linux) jA0ECQMCkyoAgBGGEaHk0koBuO9eFQZtbALsAO49ovP0cNdcqQ370gyPePz+SZeE BuUTAQs9yMTNIPzQlXE0/zjtjmoHQBWAJ+fz5zTKWouLA5JLX2gRJQMJMQ== =7TNS -----END PGP MESSAGE----- 
```
Note that there is only a 1-bit difference between both files:
```
'0' = 0x30 = 0011,0000b '1' = 0x31 = 0011,0001b 
```
Write a program to figure how many bits differ and how many bits stayed the same between message0.txt.asc and message1.txt.asc.

How many bits stay the same and how many differ?
Confusion:

You have enciphered message0.txt with the password hello. Now encipher it with the password jello. Note that there is only a 1-bit difference between both passwords:
```
'h' = 0x68 = 0110,1000b 'j' = 0x6A = 0110,1010b 
```
How many bits stay the same and how many differ?
(Partial) Defense against replay-attacks:

Now, re-encipher message0.txt with the password hello again. Exact same file, exact same password.

How many bits stay the same and how many differ?