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 public-private key pair rather than a shared secret.

PKI (Public Key Infrastructure) is a framework for issuing and managing asymmetric certificates and keys, not a symmetric cryptographic algorithm.

RSA is an asymmetric algorithm that uses mathematically linked public and private keys for encryption and digital signatures.

3DES (Triple DES) is a symmetric block cipher that applies the DES algorithm three times to each data block using one, two, or three shared secret keys that must be known by both communicating parties. Because the same key material governs both encryption and decryption, it is classified as symmetric cryptography, in contrast to RSA or DSA, which rely on mathematically related public and private keys.