Which cryptographic function is used to verify data integrity by producing a fixed-size representation of input data?

Which cryptographic function is used to verify data integrity by producing a fixed-size representation of input data?

• A. Encryption
• B. Hash function
• C. Digital signature
• D. Key exchange

Answer: (B)

To verify data integrity, you need a compact, fixed-size fingerprint of the data that you can reliably compare later. A hash function provides exactly that: it takes input of any length and produces a fixed-size digest. Its properties—deterministic output, resistance to preimage finding, and collision resistance—mean that even a small change in the data yields a dramatically different digest, and you can’t practically recover the original data from the digest. By computing the hash of the original data and later recomputing and comparing it, you can detect alterations with high confidence. Encryption, on the other hand, transforms data into unreadable ciphertext to protect confidentiality, not to provide a stable, comparable fingerprint for integrity. A digital signature does involve integrity, but it serves authenticity and non-repudiation by signing the data (or its hash) with a private key, not by producing the fixed-size representation itself. Key exchange is about establishing a shared secret and does not generate a digest for integrity checks.

To verify data integrity, you need a compact, fixed-size fingerprint of the data that you can reliably compare later. A hash function provides exactly that: it takes input of any length and produces a fixed-size digest. Its properties—deterministic output, resistance to preimage finding, and collision resistance—mean that even a small change in the data yields a dramatically different digest, and you can’t practically recover the original data from the digest. By computing the hash of the original data and later recomputing and comparing it, you can detect alterations with high confidence.

Encryption, on the other hand, transforms data into unreadable ciphertext to protect confidentiality, not to provide a stable, comparable fingerprint for integrity. A digital signature does involve integrity, but it serves authenticity and non-repudiation by signing the data (or its hash) with a private key, not by producing the fixed-size representation itself. Key exchange is about establishing a shared secret and does not generate a digest for integrity checks.