Breaking the Vigenère Cipher :Java Programming: Arrays, Lists, and Structured Data (Java Programming and Software Engineering Fundamentals Specialization) Answers 2025

1. Question 1 — Language of secretmessage3.txt

✔️ English
❌ Danish
❌ Dutch
❌ French
❌ German
❌ Italian
❌ Portuguese
❌ Spanish

2. Question 2 — First line of decrypted secretmessage3.txt

✔️ “The sea, once it casts its spell, holds one in its net of wonder forever.”

(This is the decrypted first line of secretmessage3.)

3. Question 3 — Language of secretmessage4.txt

✔️ German
❌ Danish
❌ Dutch
❌ English
❌ French
❌ Italian
❌ Portuguese
❌ Spanish

4. Question 4 — First line of decrypted secretmessage4.txt

✔️ “Der Ozean ist eine Welt voller Wunder.”

(This is the correct decrypted first line.)

5. Question 5 — Key length that gives no information

✔️ Exactly the message length
❌ 1/26 the message length
❌ Half the message length
❌ There is no key length that ensures unbreakable Vigenère

(When the key = message length and truly random → one-time pad, perfectly secure.)

6. Question 6 — When algorithm could fail

✔️ The language of the original message has multiple letters of comparable high frequency.
✔️ The language is not in the dictionaries.
✔️ The language has an unusual highest-frequency letter.
✔️ Written-sentence frequencies differ from dictionary frequencies.
✔️ The language has many characters not in the English alphabet.

(All are correct.)

7. Question 7 — What could be a problem?

✔️ The key length is long compared with the message.
❌ The message is long compared with the key length
❌ Neither