4.5.6 Representing images, sound and other data Flashcards
What is encryption?
The process of scrambling data so that it cannot be understood if intercepted in order to keep it secure during transmission.
What is plaintext?
Unencrypted information
What is ciphertext?
Encrypted information
What is a cipher?
Type of encryption method
What is needed to decrypt ciphertext?
You must know the encryption method used and the key used to encrypt the method
How do Caesar ciphers work?
- Information is encrypted by replacing characters.
* One character is always replaced by the same character
What are the two types of caesar cipher?
Shift Cipher
Substitution Cipher
How does shift cipher work?
- All of the letters in the alphabet are shifted by the same amount.
- Amount by which characters are shifted forms the key
How do substitution cipher work?
Letters are randomly replaced
What is the disadvantage of cipher caesars?
- Easily cracked
- The frequency at which each character occurs can provide a clue, one a single character is discovered, a shift cipher can be completely cracked as the key is found.
Substitution ciphers are still relatively easy to crack.
What is a one pad cipher?
Each key should only ever be used once.
What kind of cipher is vernam?
One time pad cipher
What does the Vernam cipher require?
Key should be random and at least as long as the plaintext that is to be encrypted
How does Vernam cipher work?
- Aligning the characters of the plaintext and the key
- Converting each character to binary, using an information coding system.
- Applying a logical XOR operation to the two bit patterns
- Converting the result back to a character
Why is Vernam cipher completely secure?
• The key used is chosen at random, the ciphertext is also random so it is considered completely secure.
