Key Exchange Protocols #

Key Exchange Protocols are used to exchange the shared secret key of a symmetric & asymmetric encryption scheme over an insecure channel.

Diffie Hellman Key Exchange #

Used for symmetric encryption schemes.

Theory #

Mathematics #

Security #

The security of Diffie-Hellman relies on the fact that given a large prime p, a generator g, and the values of g^a mod p and g^b mod p, it is computationally difficult to calculate the value of S = g^(ab) mod p.

This is known as the discrete logarithm problem, and no efficient algorithm is currently known to solve it for large prime numbers.

Public Key Encryption Key Exchange (PKEKE) #

Mainly used for asymmetric encryption schemes but can be used to share the key for symmetric encryption.

Theory #

Public key cryptography involves a key pair.

A public key is only used to encrypt the message and only the corresponding private key is used to decrypt the message.

The symmetric key is encrypted using the recipients public key and transmitted over the insecure channel. On the other end, the recipient uses their private key to decrypt the symmetric key. Now the shared symmetric key can be used to encrypt the communication.

Key Exchange Vulnerabilities #

Key Exchange protocols only protect against eavesdropping attacks.

Key Exchange protocols are not secure against Man-in-the-Middle attacks. Messages can be intercepted and tampered with by an adversary during key exchange.

RSA Encryption solves this problem.