Grade 9 Code Breaking Challenge
This worksheet introduces grade 9 students to basic code breaking techniques including Caesar ciphers, substitution ciphers, and frequency analysis.
Includes
Standards
Grade 9 Code Breaking Challenge
Name:
Date:
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Welcome, aspiring cryptographers! This worksheet will test your skills in decoding various ciphers. Read each question carefully and use your problem-solving abilities to break the codes.
Section 1: Caesar Cipher
A Caesar cipher shifts each letter in the plaintext a certain number of places down or up the alphabet. For example, with a shift of 3, A would become D, B would become E, and so on.
1. Decode the following message, which was encrypted using a Caesar cipher with a shift of 3 (each letter was shifted 3 places forward in the alphabet).
Encrypted Message: WKH TXLFN EURZQ IRA MXPSV RYHU WKH ODCB GRJ
2. If the letter 'G' is encrypted as 'J' using a Caesar cipher, what is the shift value?
1
2
3
4
Section 2: Simple Substitution Cipher
In a simple substitution cipher, each letter in the plaintext is replaced by a different letter or symbol. The key is a mapping of each letter to its substitute.
3. Using the substitution key below, decode the following message:
Key: A=Z, B=Y, C=X, D=W, E=V, F=U, G=T, H=S, I=R, J=Q, K=P, L=O, M=N, N=M, O=L, P=K, Q=J, R=I, S=H, T=G, U=F, V=E, W=D, X=C, Y=B, Z=A
Encrypted Message: GSV HLM RH RM GSV VZHG
4. A simple substitution cipher is generally harder to break than a Caesar cipher.
True
False
Section 3: Frequency Analysis
Frequency analysis is a technique used to break substitution ciphers by counting the occurrences of each letter in the ciphertext and comparing them to the known frequencies of letters in the original language (e.g., 'E' is the most common letter in English).
5. Consider the following encrypted message:
Encrypted Message: LDPW LV IXQ
If 'L' is the most frequent letter in the ciphertext and you suspect it represents 'E' (the most frequent letter in English), what is the likely plaintext of the message?
Section 4: Terminology
6. The original message before encryption is called the .
7. The encrypted message is referred to as the .
8. The method used to encrypt or decrypt a message is called a .
Section 5: Decryption Challenge
9. You intercept a secret message: "KHOOR ZRUOG". You know it's a Caesar cipher, but you don't know the shift. Try different shifts to decrypt the message. What is the original message and what was the shift?