Ciphers Flashcards
What is symmetric encryption?
Private-key encryption. The same key is used to encrypt and decrypt a message. The key is typically the recipient private key.
What is asymmetric encryption?
Public-key encryption. The sender uses the recipients public key to encrypt a message and the recipient uses their private key to decrypt the message.
What is Kirchhoff’s Principle?
Security/secrecy only depends on the key and cannot be solved without the key.
What is “Security by Obscurity”?
Assuming a system is more secure if a hacker doesn’t know the encryption/decryption protocol.
What is the encryption method for a Caesar/Shift Cipher?
Given a key k and a message m, shift every character of m by k places in the alphabet.
What is the decryption method for a Caesar/Shift Cipher?
Shift every character by -k places.
How strong is the security of a Caesar/Shift Cipher?
Very weak. Key space is very small, as a result messages are prone to Brute-force attacks or frequency analysis.
What are the keys for a Substitution Cipher?
All permutations (possible combinations) of the Alphabet.
What is the encryption method for a substitution Cipher?
Apply the permutation given by the key to every character of the string.
What is the decryption method for the Substitution Cipher?
Apply the inverse permutation to every character of the string.
What is the security of the Substitution Cipher?
There are 26! possible keys making a Brute-Force Attack infeasible even with modern software. Still prone to Frequency Analysis attacks.
How are keys generated by a One-Time Pad?
Uniformly at random.
What is the encryption method for a One-Time Pad?
Bitwise addition mod 2 or bitwise XOR
What are some properties of initialisation vectors (IV)?
- Uniqueness
- Non-predictable
- Random
- Length Compatible
What is a known ciphertext attack?
Attacker is given a ciphertext and tries to find the corresponding plaintext
