What is referred to as a unique digital identifier that represents data received as input?

The term that best describes a unique digital identifier representing data received as input is indeed the hash digest. A hash digest is the output of a hash function after it processes the input data. It produces a fixed-size string of characters that is unique to the specific input data, meaning even a small change in the input will result in a significantly different hash digest. This property makes hash digests especially useful for verifying data integrity, allowing users to confirm that data has not been altered.

In the context of cryptography and data security, hash digests are widely used in various applications, such as generating checksums, validating file integrity, and securing passwords. They serve to uniquely identify data without revealing the actual data itself, as a hash is not reversible.

While hash keys, encryption keys, and digital signatures also play important roles in security, they have different functions. A hash key is often used in relation to storing and retrieving data efficiently rather than identifying unique inputs. An encryption key is used for transforming data to protect its confidentiality, and a digital signature serves to verify the authenticity and integrity of a message or document, but it is not strictly a unique identifier for the input data itself.