Caesar Cipher
Yaser Rahmati | یاسر رحمتی
If you're interested in the process of creating a cipher similar to what might have been used in ancient times, I can guide you through that. For the purpose of this explanation, I'll teach you the Caesar Cipher, which is a type of substitution cipher where each letter in the plaintext is shifted a certain number of places down or up the alphabet.
Step-by-Step Guide to the Caesar Cipher
Step 1: Choose a Shift Value
The Caesar Cipher requires you to choose a "shift" value. This is the number of positions each letter in your plaintext will be moved in the alphabet.
For example, if you choose a shift of 3, A becomes D, B becomes E, and so on.
Step 2: Write Down the Alphabet
Write down the alphabet in a straight line:
Step 3: Create the Shifted Alphabet
Below the regular alphabet, write a second line starting from the letter that is the number of positions you’ve chosen (in this case, 3 positions ahead).
Here, A is mapped to D, B is mapped to E, and so on.
Step 4: Encrypt Your Message
Replace each letter in your plaintext with the corresponding letter in the shifted alphabet.
For example, let's encrypt the message "HELLO" using a shift of 3.
H -> K
E -> H
L -> O
L -> O
O -> R
The encrypted message is "KHOOR".
Step 5: Decrypt the Message
To decrypt, you simply shift the letters in the opposite direction.
Using the same example, to decrypt "KHOOR" back to "HELLO":
K -> H
H -> E
O -> L
O -> L
R -> O
The decrypted message is "HELLO".
Example: Encrypting a Complete Sentence
Let's encrypt the sentence "ARCHIMEDES CIPHER" with a shift of 4.
Write down the alphabet and shifted alphabet:
Replace each letter:
A -> E
R -> V
C -> G
H -> L
I -> M
M -> Q
E -> I
D -> H
E -> I
S -> W
(Space remains a space)
C -> G
I -> M
P -> T
H -> L
E -> I
R -> V
The encrypted message is "EVGLMIQIWI GMTLIV".
Summary
The Caesar Cipher is a simple substitution cipher where each letter in the plaintext is shifted a certain number of places down or up the alphabet.
The shift value determines how much each letter is shifted.
To encrypt, replace each letter with the corresponding one in the shifted alphabet.
To decrypt, reverse the process.
Keywords
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