topic 12 - cryptography 1

Question 1

what is a cryprosystem?

Answer 1

Disguises messages, allowing only selected people to see through the disguise.

Question 2

what is crytpography?

Answer 2

the science of designing, building, and using cryptosystems.

Question 3

what is cryptoanalysis?

Answer 3

Is the science of breaking a cryptosystem.

Question 4

what is cryptology?

Answer 4

Is the study of cryptography and cryptanalysis

Question 5

what are the applications of cryptography?

Answer 5

Primarily military use until early 80s

In US export of software and hardware encryption is controlled (terror states).

Now very much in the public domain – helps prevent online fraud:
- E-commerce.
- Internet banking etc.

Question 6

what are the two basic methods for disguising messages?

Answer 6

• Transposition: Letters rearranged into a different order.
• Substitution: Letters replaced by other letters or symbols.

Question 7

how does a simple transposition encryption work?

Answer 7

Plain text message for encryption is:
SECURITY BEGINS WITH YOU

Choose a keyword (password) and send this to the recipient using a secure channel: TEACUPS

1. Write the key horizontally as the heading for columns.
2. Assign numerical values to each letter based on the letter’s order of appearance in the alphabet.
3. Align plaintext message across each column.
4. Read down each column according to the ordinal value (col A1 first followed by col C2 etc).