CybersecurityLesson 2 of 2 in the course Cryptography

Cryptographic Hashes: Properties, Constructions, and Security Uses

5 flashcards · 5 quiz questions · 5 match pairs · 4 fill-in sentences · English

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Summary

A cryptographic hash function turns data of any length into a fixed-size value called a digest. This lesson introduces how hashing works and why it is useful.

A cryptographic hash function (CHF) maps an arbitrary binary input string, often called a message, to a binary output of a fixed length. If the output has nn bits, there are 2n2^n possible digest values, regardless of the input length.

All flashcards

Digest
The fixed-length value produced when a hash function processes a message.
Avalanche effect
The desirable behavior in which a small input change produces a substantially different-looking digest.
Password salt
A random, non-secret value stored with a password record and combined with the password before derivation.
HMAC
A keyed message authentication code built from a hash function using a structured keying method.
Proof-of-work
A task designed to be costly to find a solution for but easy to verify.

Quiz questions

  1. For an ideal hash with an n-bit digest, about how much generic work is needed to find a collision?Answer: About 2n/22^{n/2} trials, due to the birthday effect.
  2. What is the key distinction between a second pre-image search and a collision search?Answer: A second pre-image search fixes one message; a collision search lets the attacker choose both.
  3. What is a length-extension attack against some Merkle–Damgård hashes?Answer: Using a known hash and message length to calculate a hash for the message with additional data appended.
  4. Why are MD5 and SHA-1 unsuitable for applications requiring collision resistance?Answer: Practical collision attacks have been demonstrated against both algorithms.
  5. What is the purpose of unambiguous padding in a Merkle–Damgård hash construction?Answer: To ensure message blocks, including the final block, are processed without ambiguous message interpretation.

Based on the Wikipedia article Cryptographic hash function, licensed CC BY-SA 4.0. Adapted into a summary, flashcards and quizzes.

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