RFC 1321 describes which hash function?

RFC 1321 specifically describes the MD5 hash function, which was developed by Ronald Rivest in 1991. This document outlines the structure of the algorithm, its design philosophy, and the details of how it processes input data into a fixed-size (128-bit) hash value. MD5 has been widely used for verifying the integrity of data, although it is no longer considered secure against certain types of attacks.

The other options refer to different hashing algorithms that are defined in other RFCs or specifications. For instance, SHA-1 is documented in RFC 3174, RIPEMD is detailed in ISO/IEC standards, and GOST is defined by Russian cryptographic standards. Understanding the context of each of these hash functions, along with their specific RFCs or documents, is essential for recognizing their unique characteristics and applications in data integrity and security.