## Final Exam Study Guide - 810:023 Spring 2010 May 5th, Wednesday - 8 a.m. until 9:50 a.m.

1. The QUIZ TWO study guide is a big portion of the final exam study guide.
2. Encrypt the following message using Caesar encryption with the key = 3. MISSISSIPPI RIVER
```
ABCDEFGHIJKLMNOPQRSTUVWXYZ
DEFGHIJKLMNOPQRSTUVWXYZABC

A becomes D,
B becomes E,
C becomes F,
...  , Y becomes B, and
Z becomes C
when Caesar key = 3 and you are ENCRYPTING the original message.
```
3. The following cipher text was encrypted using a Caesar encryption key 3. Decrypt it to the plain text original message. FRQQHFLRQ
```ABCDEFGHIJKLMNOPQRSTUVWXYZ
DEFGHIJKLMNOPQRSTUVWXYZABC

A becomes D, B becomes E, C becomes F,  ...  , Y becomes B, and Z becomes C when Caesar key = 3.

To decrypt, you go backwards 3 letters.
So the ciphertext message has D becoming A,
E becoming B, ...
...
A becoming X,
B becoming Y, and
C becoming Z

when you DECRYPT from cipher text to plain text.

Plain text is the term for the original, readable, unencrypted message.
```
4. The Vignere encryption key is BE, your favorite length two Vignere key. Also known as 14, i.e. you can either say "BE" or use the two digit number "14" to describe the encryption key. Encrypt MISSISSIPPIRIVER using Vignere encryption with key BE = 14.
5. Decrypt the following cipher text. The cipher text was encrypted using the length two KEY 21, also known as CB. "21" = "CB"
6. ```wokqcovigsugkocmgycnu    is the cipher text.  You have to do this by hand, with paper and pencil!
A becomes a C (2 letter shift) if A was an ODD  letter, 1st, 3rd, 5th, etc.
A becomes a B (1 letter shift) if A was an EVEN letter, 2nd, 4th, 6th, 8th, etc.

Thus the code used to ENCRYPT, to create the CIPHER TEXT is CB.
21.

ABCDEFGHIJKLMNOPQRSTUVWXYZ                     ABCDEFGHIJKLMNOPQRSTUVWXYZ
CDEFGHIJKLMNOPQRSTUVWXYZAB                     BCDEFGHIJKLMNOPQRSTUVWXYZA

2 letter shift, also called                    1 letter shift, also called
code C, because A becomes C                    code B, since A becomes B, when encrypting the message to ciphertext.
when encrypting to cipertext...

C becomes A when decrypting                    B becomes A when decrypting ciphertext back to plaintext, back to the message.
back to plaintext!

2                                              1
C                                              B
C                                              B      =  CB
2                                              1      =  21

```
7. Pixels and Phosphors - RGB graphics - how color works on a computer monitor. See you handout.
8. Be able to fill in the IP numbers or the MAC addresses or the PORT numbers for the header of a packet at the 3 different levels: Data Link layer (MAC or NIC or NAC address = 48 bits) and the Network layer (IP address - 4 octets - 32 bits) and the TRANSPORT layer level (Ports like port 22 or port 80).
9. Know a few basics about the sunny.uni.edu computer and folders, also known as directories, etc.
```bash-2.03\$  mkdir MAY4th

bash-2.03\$  cd MAY4th

bash-2.03\$  pwd
/export/home/jacobson/MAY4th

bash-2.03\$  ls -a
.   ..                            What are     ..    and    .   for?

bash-2.03\$  ls ../*b*.txt
../bc.txt                              ../lastMondayFeb22nd.txt
../bc55.txt                            ../whoWasHereOnFeb25in025.txt
../bcOutput.txt
../whoWasHereOnFridayJoanOsbourne.txt

WHAT DO ALL THESE FILES ABOVE HAVE IN COMMON????

They all contain the letter b, lowercase b!

ls ../*b*.txt
-
*b*.txt   means match or find all files
that contain a little b anywhere,
and end in the extension .txt

* characters are called wildcards!
---------

bash-2.03\$ cp   ../bc55.txt    .     NOTE THE USE of ..    and    .
--             -                     --           -
..             .                     ..           .
--             -                     --           -
parent         current               parent       current
directory      directory             folder       folder

bash-2.03\$ ls -a
.         ..        bc55.txt

bash-2.03\$ ls -a                    ls for list files and folder
-         --        --------
.         ..        bc55.txt        -a    for all   -a = -all
-         --        --------                              ---
.         ..

bash-2.03\$  cp   ../bc55.txt    .

COPY = cp
copy the parent directory file named bc55.txt
to the current directory

bash-2.03\$  ls -l
-rw-r--r--   1 jacobson faculty      122 May  4 15:04 bc55.txt

-rw-r--r--   1 jacobson faculty      122 May  4 15:04 bc55.txt
110100100
6  4  4

bash-2.03\$  mkdir may5th

bash-2.03\$  ls -l
-rw-r--r--   1 jacobson faculty      122 May  4 15:04 bc55.txt
drwxr-xr-x   2 jacobson faculty     4096 May  4  2010 may5th

-rw-r--r--   1 jacobson faculty      122 May  4 15:04 bc55.txt
110100100
6  4  4

drwxr-xr-x   2 jacobson faculty     4096 May  4  2010 may5th
111101101
7  5  5

The d that starts the -l LOOOOOOOOOOOONG listing for may5th folder
indicates that may5th is a FOLDER, is a
directory.
-
mkdir may5th
created that folder named may5th.

mkdir        is short for make directory
- -  ---
m k  dir  =   mkdir
- -  ---      -----

bash-2.03\$  pwd
/export/home/jacobson/MAY4th

bash-2.03\$  cd may5th

bash-2.03\$  pwd
/export/home/jacobson/MAY4th/may5th

bash-2.03\$  ls ../../*.c
../../tortois.c        ../../tortoisSlower.c

bash-2.03\$ cp ../../*.c    .

bash-2.03\$ ls -l
-rwx--xr-x   1 jacobson faculty     2405 May  4  2010 tortois.c
-rw-r--r--   1 jacobson faculty     2415 May  4  2010 tortoisSlower.c

Q1: What number was used to change the permissions on the tortois.c
file, given the output of LS minusL (ls -l) that is shown below?

bash-2.03\$ chmod ???  tortois.c

bash-2.03\$ ls   -l tortois.c
--wx-w-r-x   1 jacobson faculty     2405 May  4  2010 tortois.c

Q2: Given that chmod 762 was just done on the tortoisSlower.c file,
show what the 9 characters would be that the LS minusL command
would exhibit?   Note:  What would you see instead of #########?

bash-2.03\$ chmod 762  tortoisSlower.c

bash-2.03\$ ls   -l   tortoisSlower.c
-#########   1 jacobson faculty     2415 May  4  2010 tortoisSlower.c

Each # has to either be a r for read or w for write or x for execute
-             -              -
or else is a hyphen indicating that
given r or w or x permission is NOT allowed.
-    -    -               ---

HERE ARE THE CORRECT ANSWERS Explained and SHOWN to the above question:
The answers are for checking your work to make sure it is correct!
-------

bash-2.03\$ ls   -l
--wx-w-r-x   1 jacobson faculty     2405 May  4  2010 tortois.c
011010101
wx w r x

011 = 3    CHMOD 325    i.e.   chmod 325 tortois.c
010 = 2                              ---
101 = 5                              ---    011 010 101
3   2   5
-wx -w- r-x
0   0 0  0
11  1  1 1
011 010 101
3   2   5

-rwxrw--w-   1 jacobson faculty     2415 May  4  2010 tortoisSlower.c
111110010
7  6  2
111 = 7
110 = 6
010 = 2

bash-2.03\$ chmod 325  tortois.c
bash-2.03\$ chmod 762  tortoisSlower.c

bash-2.03\$ ls   -l
--wx-w-r-x   1 jacobson faculty     2405 May  4  2010 tortois.c
-rwxrw--w-   1 jacobson faculty     2415 May  4  2010 tortoisSlower.c

```
10. See item number 4 and item number 8 (LI 4 and LI 8) in the PERL random quotes concepts help file.
```4.  What do the permissions need to be for the random.cgi file?

8.  See cd cgi    and     cd ..     and     pwd

and answer in context the practice questions shown on that page:

Question to find the answer for:
What would be output right now if I do the following command?

ls ..

What would be output right now if I do the following command?

ls -l     LS minus L   or LS hyphenL for ls -l

```