Explanation

Symmetric encryption uses a single key that needs to be shared among the people who need to receive the message while asymmetric encryption uses a pair of public key and a private key to encrypt and decrypt messages when communicating.

Asymmetric encryption takes relatively more time than the symmetric encryption.

Diffie Hellman algorithm is an asymmetric algorithm used to establish a shared secret for a symmetric key

algorithm. Nowadays most of the people uses hybrid crypto system i.e, combination of symmetric and

asymmetric encryption. Asymmetric Encryption is used as a technique in key exchange mechanism to share secret key and after the key is shared between sender and receiver, the communication will take place using symmetric encryption. The shared secret key will be used to encrypt the communication.

Triple DES (3DES), a symmetric-key algorithm for the encryption of electronic data, is the successor of DES (Data Encryption Standard) and provides more secure encryption then DES.

Note: Although “requires secret keys” option in this question is a bit unclear but it can only be assigned to

Symmetric algorithm.