Lecture 1 Flashcards
What are the three steps in cryptography?
- Precisely identify a threat model (CPA, CCA, etc.) 2. Propose a construction (solution) 3. Prove that breaking the construction would mean solving a hard problem
What is a cipher?
The algorithm to encrypt and decrypt plaintext
What is the main property of a cipher?
Applying encryption followed by decryption should result in the same plaintext
Ciphertext only attack
You only have a singular ciphertext and you are trying to figure out the plaintext (hardest attack)
Known Plaintext Attack
You know plaintext and ciphertext and now you are reverse engineering it to figure out the key
Chosen plaintext attack (CPA)
Eve can pick a plaintext to send to challenger and can send any number of plaintexts to help her detect key
Chosen Ciphertext Attack (CCA)
Eve can send challenger both plaintext to encrypt and ciphertext to decrypt until she figures out the key (MOST powerful attack)
What is symmetric encryption?
You use the same secret key to both encrypt and decrypt the ciphertext (so both parties need to know the key)
Why does Kerckhoff’s principle make sense?
The principle states that the security of an encryption scheme should rely on the secrecy of the key not the encryption algorithm. This makes sense because keeping an algo secret means if it gets leaked you have to change the whole scheme vs just changing the key. Also the key is easier to hide than a whole algorithm scheme.
One time key concept
The key is used to encrypt only one message
Many time key
Key can encrypt multiple messages
What are the two cones of cryptography?
Establishing a secret key, securing communication (from attackers)
Vignere Cipher
Key repeats itself (CryptoCrypto), To decrypt you subtract key from ciphertext (but breakable if you know the length of the key)
What is important about the property of XOR?
If you xor a random variable with a uniform independent random variable, you get a uniform random variable (creates randomness)
