Which is NOT a property of secure hash functions?

• A. Deterministic output
• B. Collision resistance
• C. Reversible encryption
• D. Fixed output size

Answer: (C)

Secure hash functions have several key properties that ensure their effectiveness in cryptographic applications. One of the primary characteristics is that they produce a deterministic output, meaning that the same input will always yield the same hash value, regardless of when it is processed. This property is crucial for verifying data integrity since you need to be able to recreate the hash from a given input reliably.

Another essential property is collision resistance. This means that it is computationally infeasible to find two different inputs that produce the same hash output. Collision resistance helps to ensure the uniqueness of hash values for distinct pieces of data, which is particularly important in many security protocols and applications.

A fixed output size is also a defining feature of secure hash functions. Regardless of the size of the input data, the hash function produces a hash output of a consistent length. This property simplifies aspects of security design and ensures uniformity in processing.

Reversible encryption, on the other hand, is not a property of secure hash functions. Secure hashes are designed to be one-way functions, meaning that it is not possible to reverse-engineer the original input from the hash output. This characteristic supports data integrity checks and authenticity without compromising the original data, which aligns with the general purpose of hash functions in security and privacy