Which of the following is a hashing algorithm?

MD5 (Message Digest Algorithm 5) is a one-way cryptographic hash function that takes input of any length and produces a fixed 128-bit (32 hex character) hash value. It is used for integrity verification such as checksums, though it is now considered cryptographically broken for security-critical uses due to collision vulnerabilities. The key property that makes it a hash algorithm is that it is one-way and deterministic.

PGP (Pretty Good Privacy) is an asymmetric encryption and digital signing tool used for securing emails and files, not a hashing algorithm itself.

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 that shifts letters by 13 positions - it is reversible and provides no cryptographic strength, making it a cipher not a hash function.