Asymmetric Crypto Flashcards
What is one weakness of textbook RSA and how can it be mitigated?
Textbook RSA is deterministic, ie. same message will get identical ciphertext
Solution approach:
- employ padding
- add random bits
How does RSA ensures integrity?
Encryption with the private key generates a signature.
- Alice wants to sign message m for Bob
- Alice uses a cryptographic hash function h to compute h(m)
- Alice encrypts h(m) with her secret key: σ←EncKAlicesec(h(m))
- Alice sends m, σ to Bob
- Bob verifies that h(m)=DecKAlicepub(σ)
What is Hybrid encryption scheme?
Use public key cryptography to securely exchange symmetric keys. Then use the symmetric key to encrypt the actual payload.
What is Deffie hellman key exchange protocol?
It is a protocol where both ends securely exchanges cryptographic keys between two parties over a public channel without their conversation being transmitted over the internet.
How does DH key exchange work?
Person A chooses a prime number p.
He chooses another number g < p
He generates another number a < p
Computes X = g^a mod p and sends X, p and g.
Person B generates random number b.
Computes Y = g^b mod p and sends Y
Person A can compute the Key = Y^a mod p
Person B can compute the key = X^b mod p
Mention an attack against DF. Soltuion?
DH can protect against Eves dropping HOWEVER:
Eve in the MITM can trick both ends and do DH between each and everyone of them without them knowing that.
Use Authenticated DH which works with signatures.
What is perfect forward secrecy? and how does Diffie hellman ensures it?
When the attacker saves the messages for later abuse when he can at some point get access to the victims private key .
Diffie hellman generates new session key everytime theres communication. this session key is unique.
What is Threshold signature schemes? What does it ensure?
Distributing the Ksec into n shares and store them on an individual node.
It ensures Ksec confidentiality
