Hashing

Hashing runs input of any length through a one-way function to produce a fixed-length digest. Change one bit of the input and roughly half the digest bits flip: the avalanche effect, which makes digests useful fingerprints. Hashing verifies integrity (does this file still match the digest published for it), stores passwords without keeping the plaintext, and produces the message digest that a digital signature actually signs. SHA-2 and SHA-3 are current; MD5 and SHA-1 are broken by collision attacks and appear on the exam only as wrong answers.

The distinction that decides questions: hashing is not encryption. There is no key and no ciphertext; nothing is ever decrypted, because the function is deliberately irreversible. A collision (two inputs producing the same digest) breaks that guarantee, which is why collision resistance defines a hash’s strength. Passwords need salting so identical passwords hash differently, and a stolen hash can still be abused without reversing it at all, as pass the hash demonstrates.

Exam relevance: integrity is the trigger word; if a scenario verifies that data has not changed, the answer is hashing. Avalanche effect, collision, and salting all point here too. The confusable is encryption, which provides confidentiality and is reversible with the key; if a question implies getting the original data back, hashing is the wrong answer by definition.