ACARA Digital Technologies Years 9–10 Definitions Worksheet: Cyber Security Threats and Vulnerabilities (Modules 860–875)
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Date:
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Key terms
Write what each term means, in your own words.
1
frequency analysis
2
transposition cipher
3
=CODE("A")
4
=MOD(number, divisor)
5
=CHAR(MOD(CODE(A2)-65+$B$1,26)+65)
6
=CHAR(MOD(CODE(B2)-65-3,26)+65)
7
ord() and chr()
8
ch.isalpha()
9
chr((ord(ch) - 65 + shift) % 26 + 65)
10
caesar(cipher, -shift)
Answer Key
ACARA Digital Technologies Years 9–10 · Modules 860–875 · Student wording will vary for definitions
1frequency analysis — Counting how often each letter appears in ciphertext and matching the most common ones to common English letters like E, to work out a substitution cipher's key.
2transposition cipher — A cipher that keeps the same letters but changes their order, like writing a message in a zigzag across rails and then reading each rail in turn.
3=CODE("A") — Gives the number code of a letter, so =CODE("A") returns 65. Its partner =CHAR(65) turns a code back into a letter. Capital letters start at 65 (A) and run to 90 (Z).
4=MOD(number, divisor) — Returns the remainder after division, so numbers wrap around. =MOD(27,26) gives 1, which is how a Caesar shift loops from Z back to A.
5=CHAR(MOD(CODE(A2)-65+$B$1,26)+65) — Shifts the capital letter in A2 forward by the key in locked cell $B$1, wrapping Z back to A, and returns the encrypted letter. Copy it across so each cell encrypts one letter.
6=CHAR(MOD(CODE(B2)-65-3,26)+65) — Shifts a letter back by the key (3) to decrypt it. Subtracting the key undoes adding it, and MOD 26 wraps A-Z around so the result stays a letter.
7ord() and chr() — ord("A") returns the number code of a character (65). chr(65) turns a number code back into its character ("A"). Ciphers use them to change letters to numbers and back.
8ch.isalpha() — Returns True if the character ch is a letter, so a Caesar loop can shift letters and leave spaces and punctuation unchanged. ch.isupper() checks for capitals.
9chr((ord(ch) - 65 + shift) % 26 + 65) — Shifts an upper-case letter ch along the alphabet by shift, wrapping past Z back to A. A for loop applies it to each letter and builds the ciphertext with +=, skipping spaces.
10caesar(cipher, -shift) — Decrypts by calling the same Caesar function with the negative of the original shift. Shifting back by the same amount undoes the encryption, and % keeps the letters wrapping.