Cryptography - Symmetric, Asymmetric, Basics Flashcards
(65 cards)
Define
Symmetric Cryptography
Encryption key = decryption key
Algorithm for Symmetric Cryptography
- Generate key (KeyGen() => K )
- Encrypt message (E(K, M) = EK(M) = C )
- Decrypt message (D(C, K) = DK(C) = M )
What is the attacker’s goal in symmetric cryptography?
Find out any information on the message(s) or the key
What is the goal of the defender in symmetric cryptography?
The attacker shouldn’t be able to distinguish which 2 messages were encrypted in cipher
List the types of symmetric cryptography attacks
- Ciphertext
- Known plaintext
- Chosen plaintext
- Chosen ciphertext
Describe
Ciphertext Attack
Symmetric Cryptography
Eve observes every instance of Cipher and has partial information Message (i.e. knows what language was used)
Describe
Known Plaintext Attack
Symmetric Cryptography
Eve knows part of Message and/or entirty of numerous Messages
Describe
Chosen Plaintext Attack
Symmetric Cryptography
Eve picks a Message for Alice to encrypt
Describe
Chosen Ciphertext Attack
Symmetric Cryptography
Eve picks a ciphertext for Bob to decrypt
Describe
Secure Cryptic System
A costly system to break into
Why are the costs high to break into a Symmetric Crypto system?
- Expensive - exhaustion of resources and efforts
- Useful lifetime of information may expire
Probability of an Attacker winning
Symmetric Cryptography
Pr[Attacker wins] <= 50% or 1/2 + e
Describe
Pseudorandom Number Generators
Symmetric Cryptography
A random-looking value that is actually determinastically created for inital vector
Describe
Stream ciphers
Symmetric Cryptography
Encrypting a plaintext with a pseudrandom digit 1 bit/byte at a time
Pros of Symmetric Cryptography
Strong confidentiality
Cons of Symmetric Cryptography
- Weak authenticity
- Weak integrity
- Difficult to manage and distribute the secret keys
Describe
One-Time Pad
When a random key is chosen and used once for each message
How long is a one-time pad?
As long as the message itself (revealing the length of the message)
What type of secure are one-time pads?
IND-CPA and IND-KPA
What are the limits to one-time pads?
- Must be truly random and independent
- Requires secure distribution of secret keys
- A large message would make a difficult one-time pad to manage
Define
IND-KPA
When attacker can’t distinguish between 2 encryptions of the same key while knowing 2 plaintexts
Define
IND-CPA
When the attacker can’t distinguish between encryptions of different plaintext under the same key while knowing ciphertexts
Which is stronger between IND-CPA and IND-KPA?
IND-CPA
What does IND-CPA imply?
That IND-KPA also holds true
