A one-way hash is a cryptographic function that meets all the criteria described. It takes an input of arbitrary length (a string of characters) and produces a fixed-length string, known as a hash value or message digest. The core properties of a cryptographic hash function are that it is deterministic (the same input always produces the same output), fast to compute, and, crucially, "one-way." This one-way property, also known as preimage resistance, makes it computationally infeasible to determine the original input string from its hash value, meaning the transformation cannot be reversed.

B. DES: This is a symmetric-key encryption algorithm. It is a two-way, reversible process used for confidentiality, not a one-way transformation.

C. Transposition: A classical encryption cipher that rearranges the order of characters. It is reversible and does not produce a fixed-length output.

D. Substitution: A classical encryption cipher that replaces characters with other characters. It is also reversible and does not produce a fixed-length output.

1. National Institute of Standards and Technology (NIST). (2015). FIPS PUB 180-4

Secure Hash Standard (SHS). Section 1

"Introduction

" states

"A hash algorithm is used to compute a condensed representation of a message or a data file... For a given algorithm

the message digests are of a fixed length..."

2. Katz

J.

& Lindell

Y. (2014). Introduction to Modern Cryptography (2nd ed.). CRC Press. In Chapter 5

Section 5.1

a hash function is defined as a function that maps arbitrary-length strings to a fixed-length output. The property of being "one-way" is formally defined as preimage resistance.

3. Stallings

W. (2017). Cryptography and Network Security: Principles and Practice (7th ed.). Pearson. Chapter 11

Section 11.1

"Secure Hash Algorithms

" describes the fundamental requirements for a cryptographic hash function

including the one-way property (preimage resistance) and the production of a fixed-length hash value.