Question: Show me the steps to solve What is a shift cipher? Who is the shift cipher named after, and why? Describe the general process of
Show me the steps to solve
What is a shift cipher?
Who is the shift cipher named after, and why?
Describe the general process of encryption using a shift cipher.
Describe the general process of decryption using a shift cipher.
Fill In the Blank
A shift cipher, also known as a cipher, is an encryption method where each letter in the plaintext is shifted by
a fixed number of positions in the alphabet.
In a shift cipher, the number of positions each letter is shifted is known as the key.
To encrypt the letter B with a shift key of you would shift B in the alphabet.
If the plaintext letter is M and the shift key is the resulting ciphertext letter is
Encryption and Decryption
Encryption Example:
Given the plaintext HELLO and a shift key of complete the encryption:
o H
o E
o L
Classical Cryptosystems: Shift Ciphers Student Worksheet
o L
o O
Ciphertext:
Describe how you obtained the ciphertext:
Decryption Example:
Given the ciphertext KHOOR and a shift key of complete the decryption:
o K
o H
o O
o O
o R
Plaintext:
Describe how you obtained the plaintext:
Fill in the Blank
To decrypt a message encrypted with a shift cipher, you need to shift the letters in the ciphertext by the shift
key.
The shift cipher is named after Julius Caesar because he used it to protect his messages by shifting each letter
positions in the alphabet.
The ciphertext resulting from encrypting HELLO with a shift key of is
Types of Attacks
Ciphertext Only Attack:
o Describe the strategy for a ciphertextonly attack and provide an example.
Frequency Analysis:
o Explain how frequency analysis can be used to break a shift cipher and provide an example.
Fill in the Blank
Classical Cryptosystems: Shift Ciphers Student Worksheet
In a ciphertextonly attack, the attacker tries all possible shift keys, which are limited to possible values in the
case of the English alphabet.
Frequency analysis in a shift cipher involves comparing the most frequent letter in the ciphertext with the most frequent
letter in text.
Known Plaintext Attack
If you know that A encrypts to D what is the shift key?
o Shift Key:
Explain how you determined the shift key.
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A known plaintext attack allows the attacker to determine the shift key if they know both the and its
corresponding ciphertext.
If the plaintext letter A encrypts to the ciphertext letter D the shift key used for encryption is
Chosen Plaintext Attack:
If the plaintext is A and it decrypts to D what is the shift key?
o Shift Key:
Explain how you determined the shift key.
Chosen Ciphertext Attack:
If the ciphertext D decrypts to A what is the shift key?
o Shift Key:
Explain how you determined the shift key
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