Which of the following algorithms are used in symmetric encryption?

The focus here is on symmetric encryption algorithms, and the correct choice, DES (Data Encryption Standard), is a widely recognized symmetric key encryption algorithm. Symmetric encryption relies on a single key for both encryption and decryption, meaning the sender and receiver must both have access to this key and keep it confidential.

DES utilizes a fixed-size 56-bit key and operates on 64-bit blocks of data, applying a series of transformations and permutations to encrypt plaintext into ciphertext. It has been foundational in the evolution of encryption standards, although it is considered less secure by today's standards due to advances in computing power and the emergence of more robust algorithms.

Blowfish, another option, is also a symmetric encryption algorithm known for its variable-length key feature and is generally regarded as secure. However, DES is historically significant as one of the earliest symmetric encryption standards.

In contrast, ECC (Elliptic Curve Cryptography) and Diffie-Hellman are not symmetric encryption algorithms. ECC is used for asymmetric encryption, providing a method where a public key can be shared while keeping a private key secret. Diffie-Hellman is a key exchange algorithm that allows two parties to generate a shared secret key securely over an insecure channel but does not encrypt the data itself