Lesson 1: Ceasar Ciphers

[Amanda Blaine]

Welcome, class, to your first cryptography class. I am Amanda Blaine, your Headmaster, Spymaster, and very busy teacher. Let's hurry up and get started.

Shift ciphers are a form of concealing a message.

A Ceasar cipher is the most simple form of shift cipher. The alphabet is moved a predetermined number of letters to the side. Here's an example.

A

B

C

D

E

F

G

H

I

J

K

L

M

N

O

P

Q

R

S

T

U

V

W

X

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T

U

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A

B

C

D

E

F

G

H

I

J

K

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M

N

O

P

Q

R

In this key (shift +18),
Amanda Blaine would become SESFVS TDSAFW.

Homework:

Reply with your answers. Please use complete sentences. Grades will be given based on completion and accuracy.

1. What is one advantage to a Ceasar cipher? (5 pts)
2. What is one disadvantage to a Ceasar cipher? (5 pts)
3. Write your name in a (shift +5) Ceasar cipher. (For example A ==> F.) (5 pts)
4. Decipher this ceasar cipher. (shift -4 *Thanks Nathan!*) (PM this answer to me, subject ceasar ciphers) (10 pts)
AI EVI TPIEWIH XS MRJSVQ CSY XLEX CSY LEZI FIIR EGGITXIH XS WTCQEWXIV WGLSSP SJ XLI LMHHIR EVXW.

Total Possible Points: 25

[MeiMei]

MeiMei blinked, this was destined to be her worse subject and it showed. All through the class, that ghostly white face of hers was frozen with dot-like teal eyes and a lost, shocked and dumb facial expression. She even failed to write the assignment down, coming in the next day without it.

[Nathan Dark]

Nathan listened carefully to the teacher's words as she spoke, and wrote down the assignment when they got it. This subject seemed quite interesting, and Ceasar ciphers didn't seem too hard, either.

In the evening, when he got around to starting his homework, he wasn't quite as certain about the ease he would manage this with, but he started anyway.

1. What is one advantage to a Ceasar cipher? (5 pts)
It is easy to create, and gives at least a basic protection for messages. It can be solved quickly if you have the key.

2. What is one disadvantage to a Ceasar cipher? (5 pts)
It is quite easy to break if you know the key, and even if you don't, there are only so many possibilities, as long as you guess it's a Ceasar cipher.

3. Write your name in a (shift +5) Ceasar cipher. (For example A ==> F.) (5 pts)
SFYMFS IFWP.

The third one took Nathan quite a while to work out - first he did it wrong and ended up with a shift +4 - though that one looked quite cool - REXLER HEVO. After he realised he had done it wrong, though, he went back and reworked it.

Then there was the last one. At first he thought he was going to skip it completely, but then he started. The +4 shift proved to be... wrong, though, so he first thought he had done it wrong, like with his name, but when neither of the others worked either, he shrugged and gave up. Doing the rest of the tasks was just going to have to be enough.

(out of character: shouldn't that be shift -4 or shift +22? Or maybe it's just that shifts can be counted both ways, and me, and thus Nathan, just didn't realise that?)

[Harem Del Villar]

Harem sits down and listens in to the teacher.
"..."
She blinks a few times before writing down on a white sheet and then handing it to the head mistress.


1. What is one advantage to a Ceasar cipher? (5 pts)
To discreerly hand out messages on a mission and gives more protection to the document.
2. What is one disadvantage to a Ceasar cipher? (5 pts)
It is quite easy to decipher, so the privacy on docuemnts is on danger. letters can be guessed and decoded.
3. Write your name in a (shift +5) Ceasar cipher. (For example A ==> F.) (5 pts)
ROT5: MFWJR IJQ ANQQFW

4. Decipher this ceasar cipher. (shift -4 *Thanks Nathan!*) (PM this answer to me, subject ceasar ciphers) (10 pts)
AI EVI TPIEWIH XS MRJSVQ CSY XLEX CSY LEZI FIIR EGGITXIH XS WTCQEWXIV WGLSSP SJ XLI LMHHIR EVXW.

[Fredrick Nova]

Fredrick looked over the assignment slowly. He was good with things like this from years of working with music, which is based on math and can be quite complicated. The Ceasar cipher looked pretty easy, he thought, but you have to start with the basics.

He wrote his answers in his rather scribbly handwriting, pausing to blot the paper now and then. He really wasn't used to writing on parchment, all the ink seemed to pool on the surface of it.

1. A Ceasar cipher is quick for emergency use. You can use it without much thought in getting information to a partner that you don't want just anyone to be able to read. You can also leave it for people you don't want knowing your business to throw them off with false information that they will assume you wouldn't bother to code unless it was important.

2. The problem with this cipher is that it's not really that secure. People with any kind of training will be able to break it quickly. Another problem is that it might miscommunicate if your partner is used to another alphabet with fewer or more characters.

3. My name would be: KWJIWNHP STAF

4. He worked it out, using his finger and feeling something of a moron, but he was proud of himself when he was done.

He blotted the page again and went to turn his assignment in.

[mata]

Mata bit the bottom of her lip lightly when she wrote down all of the problems on a seperate piece of paper. The first two seemed easy enough but...the last two was a bit more challenging. Realising that she had no clue what she was supposed to do, Mata took out a small notebook with notes about Ceasar cipher.

She quickly scanned them and closed the book with a light 'fump'. A small grin graced her lips and she took the pencil that she had stuck on her ear and began writing down her answers.


1. What is one advantage to a Ceasar cipher? (5 pts)

Ceasar cipher can be used for hidden message that are not meant for people to see.

2. What is one disadvantage to a Ceasar cipher? (5 pts)

It can take a while to decipher a message if you only started to learn the secrets to it. But if you've been taught Ceasar cipher it will be too easy (inlcuding enemies) to figure out and cause problems.

3. Write your name in a (shift +5) Ceasar cipher. (For example A ==> F.) (5 pts)

RFYF


4. Decipher this ceasar cipher. (shift -4 *Thanks Nathan!*) (PM this answer to me, subject ceasar ciphers) (10 pts)

AI EVI TPIEWIH XS MRJSVQ CSY XLEX CSY LEZI FIIR EGGITXIH XS WTCQEWXIV WGLSSP SJ XLI LMHHIR EVXW.


"Phew! I'm glad I got this over with." She said rubbing her eyes. Staring at the paper for a half an hour didn't work well for her. She put her paper in her bag and quickly got out of her seat and stood up to go and turn in her assignment.

[Ai]

Ai looked at the homework and groaned. She knew she was in trouble as she enrolled in months after she was supposed to. She knew she had to get the work done so she started on the first question with reluctance.

1. What is one advantage to a Ceasar cipher? (5 pts)
It was so that one could pass on a message that the enemy might have difficulty to read it if they get their hands on it while the person who it was meant for coduld read it safely.

2. What is one disadvantage to a Ceasar cipher? (5 pts)
If one does not know how to decipher it, it would be quite a problem. It might take a long time for once who is not very good at the subject.

3. Write your name in a (shift +5) Ceasar cipher. (For example A ==> F.) (5 pts)
fn

4. Decipher this ceasar cipher. (shift -4 *Thanks Nathan!*) (PM this answer to me, subject ceasar ciphers) (10 pts)
AI EVI TPIEWIH XS MRJSVQ CSY XLEX CSY LEZI FIIR EGGITXIH XS WTCQEWXIV WGLSSP SJ XLI LMHHIR EVXW

When the homework was done she sighed in relief. It took a bit of brain power to decipher the last one. She thought to give it up but she never back down on a challenged. With this, she hurried to hand up the few months late homework.

[Harem Del Villar]

Harem looked back at the new student. She felt like drifting off into sleep. Something that she has been doing lately. It seems that she couldn't sleep well at night.

Harem noticed that the new student seemed to dress like he a bit. Harem was glad to know that she wasn't the only one wearing black all the time.

[Ai]

Ai feeling someone looking at her shrugged her shoulders. She felt no malice so she went back to what she was doing. Daydreaming.

[Cian O'Neil]

1. What is one advantage to a Ceasar cipher? (5 pts)

It is easy and quick to code.

2. What is one disadvantage to a Ceasar cipher? (5 pts)

It is easily broken.

3. Write your name in a (shift +5) Ceasar cipher. (For example A ==> F.) (5 pts)

Cian O'Neil ==> Hnfs T'Sjnq
4. Decipher this ceasar cipher. (shift -4 *Thanks Nathan!*) (PM this answer to me, subject ceasar ciphers) (10 pts)
AI EVI TPIEWIH XS MRJSVQ CSY XLEX CSY LEZI FIIR EGGITXIH XS WTCQEWXIV WGLSSP SJ XLI LMHHIR EVXW.

Cian checked his work again and then turned in his paper, glad to have finished one class period okay at his new school.