Cryptography - Asymmetric Algorithms

Question 1

Diffie Helman

Answer 1

Asymmetric key agreement algorithm responsible for the key agreement process

Key agreement process
1. Jim generates private and public key, Sue generates a private and public key

2. Jim and Sue share their public keys
3. D-H algorithm is applied to John’s private key and Sally’s public key on Jim’s machine and to Sally’s private key and John’s public key on Sue’s machine
4. As a result, the same shared value is created for John and Sally which in turn creates same symmetric key on each system using the asymmetric key agreement algorithm

Provides secure key distribution but not confidentiality, authentication or nonrepudiation

Susceptible to MITM attacks unless an organization implements digital signatures or certificates at the beginning of the process

Question 2

RSA

Answer 2

Most popular asymmetric algorithm

can provide key exchange, encryption, digital signatures

Uses 1024 to 4096 bit key and performs one round of transformation

If factorization of the prime numbers is used, implementation is considered breakable and shouldn’t be used

Uses one-way function to provide encryption/decryption and digital signature verification/generation

Public key works with one-way function to perform encryption and digital signature verification

Private key works with one-way function to perform decryption and signature generation

Attackers can use Number Field Sieve (NFS) a factoring algorithm to attack RSA

Question 3

El Gamal

Answer 3

based on Diffie Hellman algorithm

deals with discrete logarithms, can provide key exchange, encryption, digital signatures

Any key size can be used, performance decreases with size

Key size of 1024 bits or less recommended because it’s the slowest asymmetric algorithm

Question 4

Elliptic Curve Cryptography (ECC)

Answer 4

Provides secure key distribution, encryption, digital signatures

Can use key of any size

Can use much smaller key than RSA or any other asymmetric algorithm and still provide comparable security

Primary benefit is a smaller key size, reducing storage and transmission requirements

More efficient and better security than RSA keys of the same size

Question 5

Knapsack

Answer 5

Series of asymmetric algorithms that provide encryption and digital signatures

No longer used due to security issues

Question 6

Zero Knowledge Proof

Answer 6

Technique used to ensure that only minimum needed information is disclosed without giving all the details

i.e.
One user encrypts data with his private key and receiver decrypts data with the originator’s public key

Originator proves he has his private key simply because the receiver can read the message