Which of the following is a symmetric cryptographic standard?

DSA (Digital Signature Algorithm) is an asymmetric algorithm used exclusively for digital signatures, relying on a mathematically linked public and private key pair.

PKI (Public Key Infrastructure) is a governance framework for managing asymmetric certificates and key pairs, not a cryptographic algorithm itself.

RSA is an asymmetric algorithm based on integer factorization difficulty, using separate public and private keys for encryption and decryption.

Triple DES (3DES) is a symmetric block cipher that applies the DES algorithm three successive times to each data block, using one, two, or three 56-bit keys. It uses the same key for both encryption and decryption, which is the defining characteristic of symmetric cryptography. All other options involve asymmetric algorithms or infrastructure frameworks that rely on key pairs.