Final answer:
The function used in encryption algorithms is a hash function, which transforms the original data into a fixed-size string.
Step-by-step explanation:
In encryption algorithms, the function used for transforming the original data into a fixed-size string is called a hash function. A hash function takes an input message and produces a unique output, known as a hash value. This hash value is used as a digital fingerprint and is commonly used in encryption algorithms to ensure data integrity and security.
For example, the SHA-256 algorithm, one of the widely used hash functions in encryption, takes an input message and produces a 256-bit hash value. This hash value is unique to the input message, and any slight change in the message will result in a completely different hash value. This property makes it difficult for an attacker to modify the original message without being detected.
Therefore, option D, Hash, is the correct answer as it represents the function used in encryption algorithms.