What is a function that takes a variable-size input and returns a fixed-size string?

The function that takes a variable-size input and returns a fixed-size string is known as a hash. Hash functions are designed to accept input data of any size – whether it's a small piece of text or a large file – and produce a consistent and fixed-length output, commonly referred to as a hash value or hash code.

One of the primary objectives of hash functions is to ensure that they can yield a unique hash for different inputs and that the output has a set size regardless of the input size. For example, popular hash functions like SHA-256 always produce a 256-bit output, which is a fixed size, despite the size of the input data.

This property makes hash functions particularly useful in various applications, such as data integrity verification, password hashing, and digital signatures. The fixed-length output ensures that even large datasets can be effectively processed and compared without needing to reference the entire original data.

In contrast, other options like ciphers are algorithms used for encrypting and decrypting data, algorithms refer to systematic procedures for solving specific problems (which can encompass both encryption and hashing), and tokens are typically used in the context of authentication and identification, rather than producing a fixed-size output from variable input. Thus, the right choice clearly aligns with the characteristics