Which type of encryption algorithm uses the same key to encrypt and decrypt data?

Symmetric encryption algorithms, such as AES and DES, use the same secret key for both the encryption and decryption operations. This design is efficient for encrypting large amounts of data but requires a secure method to share the key between communicating parties beforehand.

The Diffie-Hellman algorithm is a key exchange protocol used to securely establish a shared secret over an insecure channel, not a general-purpose encryption algorithm.

Asymmetric encryption uses two mathematically related but different keys - a public key to encrypt and a private key to decrypt.

Dodecaphonic is a term from music theory referring to a 12-tone composition technique and has no relation to cryptography.