The role of cryptographic hash functions in cyber security is critical, as they ensure data integrity, authenticate information, and securely store passwords. A good hash function has several properties: it produces a unique output for each unique input (collision-resistant); it is infeasible to generate the original input from its hash output (pre-image resistant); and a small change to the input will produce a significantly different hash (avalanche effect).
- Deterministic: The same input will always result in the same hash output.
- Fixed Output Length: Regardless of the size of the input data, the output hash is always of a fixed size.
- Efficiency: Hash functions compute the hash value at a high speed.
- Pre-image Resistant: It is computationally infeasible to reverse-engineer the original input from its hash value.
- Collision Resistant: It is infeasibly hard to find two different inputs that produce the same output hash.
- Avalanche Effect: A minor change to the input should change the hash value dramatically.
- Real-World Example: When a user logs into a secure platform, the password they entered is hashed and compared with the stored hash of the actual password. If the hashes match, access is granted.
- Hypothetical Scenario: A document is digitally signed by computing its hash and then encrypting the hash with a private key. When verifying the signature, the document’s hash is recomputed and compared with the decrypted signature hash. If they match, the document’s integrity is confirmed.
- SHA-256: A widely used cryptographic hash function that produces a 256-bit hash value.
- MD5: An older hash function that produces a 128-bit hash, now considered insecure due to vulnerabilities.
- Collision: The event where two different inputs produce the same hash output, which hash functions are designed to avoid.