What is an example of a "one-way" cryptographic function?

A "one-way" cryptographic function is designed to take an input and generate a fixed-size output in such a way that it is computationally infeasible to retrieve the original input from the output. This makes it an essential component in ensuring data integrity and secure password storage, as it allows verification without revealing the original data.

SHA-2 is part of a family of hash functions that serve as classic examples of one-way cryptographic functions. These hash functions take an input (or message) and produce a unique hash value, which is a fixed-length string that represents the data. It is extremely difficult to generate the original input from the hash value, making it effectively a one-way process.

In contrast, Rijndael (which is the algorithm behind AES) and DES are symmetric encryption algorithms. They are designed to be reversible—meaning you can encrypt data and also decrypt it back to its original form. RSA, being an asymmetric encryption algorithm, is also designed for reversibility through the use of a public and private key pair, allowing for encryption and decryption.

Thus, SHA-2 is correctly identified as a one-way cryptographic function due to its property of producing an output that cannot be reversed to reveal the original input.