What is the main security service a cryptographic hash provides?

While cryptographic hashes provide integrity and are computationally efficient, 'ease of computation' is a desirable performance characteristic, not a security service in itself.

Cryptographic hash functions alone do not provide message authentication; this typically requires the use of a secret key (e.g., HMAC). They do aim for collision resistance, but message authentication is not an inherent service.

While integrity and collision resistance are key aspects, 'computational in-feasibility' more broadly encompasses the difficulty of breaking the hash's security properties, including preimage resistance, which is fundamental to its integrity guarantees.

A cryptographic hash's main security service is ensuring data integrity, where any modification to the data results in a different hash value. This integrity is critically supported by the computational in-feasibility of reversing the hash (preimage resistance) or finding inputs that produce the same hash (collision resistance), making tampering practically impossible to conceal.