Which of the following is a hashing algorithm?

MD5 (Message Digest 5) is a one-way hashing algorithm that takes arbitrary input and produces a fixed-length 128-bit hash value, making it impossible to reverse-engineer the original data from the digest alone. It is commonly used for file integrity verification and stored password hashing, though it is now considered cryptographically broken for security-sensitive uses.

PGP (Pretty Good Privacy) is a data encryption and digital signing program that uses asymmetric and symmetric encryption - it is not a hashing algorithm.

DES (Data Encryption Standard) is a symmetric-key block cipher used for encrypting data, not a hashing algorithm.

ROT13 is a simple Caesar cipher substitution encoding that shifts letters by 13 positions - it is reversible and provides no cryptographic integrity, so it is neither a hash function nor a secure algorithm.