Cryptography and Hash Functions Quiz

Cryptography and Network Security - Week 9-11

• Message Integrity: Cryptography systems often provide secrecy but not integrity. Integrity is crucial in situations where secrecy isn't required, ensuring the data hasn't been tampered with.

• Document and Fingerprint: A practical analogy for preserving document integrity is using a fingerprint. Alice, for example, can add her fingerprint to a document as a way to verify that the content hasn't changed.

• Message and Message Digest: In computing, the electronic equivalent of a fingerprint and document pair is the message and its digest. A hash function maps the message to the digest, also called the "fingerprint."

• Difference between Document/Fingerprint and Message/Digest: Documents and fingerprints are physically linked. Messages and digests can be unlinked, crucial for integrity checks. The digest itself must be protected from change for accurate verification.

• Checking Integrity: Integrity checking involves two steps: a hash function processes the message, producing a digest; this current digest is compared with a previous/stored digest. If they match, the integrity is verified. If the digests differ, there is an indication that the message has been altered.

• Cryptographic Hash Function Criteria: Preimage resistance, second preimage resistance, and collision resistance are essential requirements for a cryptographically secure hash function.

• Preimage Attack: Given a hash value, a preimage attack attempts to find the original message that produced this hash.

• Second Preimage Attack: Given a message and its hash, a second preimage attack aims to find another message that hashes to the same value.

• Collision Attack: This attack attempts to find two different messages that produce the same hash value.

• Random Oracle Model: An ideal mathematical model of a hash function, introduced in 1993 by Bellare and Rogaway, is the Random Oracle Model. This is an idealized model which assumes that the hash function behaves randomly.

• Message Authentication Code (MAC): A MAC is a modification detection code, a cryptographic hash function that authenticates the sender of a message. Unlike a message digest, a MAC requires a shared secret key.

• Modification Detection Code (MDC): An MDC, while useful for detecting changes, does not authenticate the sender of a message.

• Nested MAC: A nested MAC involves applying a hash function twice with a different secret key for each iteration (or applying the MAC function iteratively).

• Symmetric Message Encryption: Symmetric encryption can provide authentication in addition to confidentiality. The receiver knows only the sender and receiver have the key if used correctly.

• Public-Key Message Encryption: Public-key encryption does not necessarily confirm the sender's identity. Signing with a private key and encrypting with a public key adds both authentication and confidentiality.

• Message Authentication Code (MAC) Properties: A MAC is a cryptographic checksum; it condenses a variable-length message into a smaller, fixed-size value using a secret key, and it's a many-to-one function. Finding two matching messages with the same MAC should be computationally infeasible.

• HMAC (Hash-based Message Authentication Code): A widely used MAC based on hash functions, making it often more efficient & adaptable than other approaches.

• Hash Function Requirements: A hash function should be efficient, use variable input sizes, produce fixed-length outputs, resist preimage and second-preimage attacks, and be resistant to collision attacks.

• Birthday Attacks: These attacks exploit the mathematical property of hash functions to find collisions faster, thus reducing their security level if the hash sizes are too small.

• Hash Function Cryptanalysis: Analysis techniques used find weaknesses in a hash function which allow attacks to exploit them faster than brute force.

• Block Ciphers as Hash Functions: Block ciphers can be used to create hash functions, but the resulting hash values are often too small and susceptible to various attacks.

• Secure Hash Algorithm (SHA): A family of cryptographic hash functions designed by NIST and NSA, widely considered secure. Included in the family are SHA-1, SHA-2 (256, 384, 512), and SHA-3 (Keccak).

• SHA-3 Requirements: These include the requirements and features/characteristics of SHA-3 (Keccak).

• Padding and Length Field in SHA-512: Padding and length fields are necessary to prepare a message of variable length for processing ensuring that the length of the message is correctly interpreted and processed.

• Whirlpool Hash Function: A keyed hash function designed in the similar structure/style of other well-known methods like MD4.

• Whirlpool Cipher: A cipher that uses a 512-bit block size.

• Decryption & Verification: A digital signature scheme allows for straightforward verification of the message's integrity and authentication. Methods to overcome weaknesses in this verification process exist.

• Attack Types: Key-Only Attacks, Known-Message Attacks, Chosen-Message Attacks are the three basic categories of an attack aimed at breaking the security of digital schemes.

• Forgery Types: Existential forging, selective forging, and total breaks are types of attacks that target creating a valid signature without having access to the private key of the signer.

• Digital Signature Schemes: This include RSA, ElGamal, Schnorr, DSS, and ECDSA.

• RSA Digital Signature Scheme: General idea behind the RSA digital signature scheme, covering signing and verification, and key generation.

-ElGamal Digital Signature Scheme: General idea behind the ElGamal digital signature scheme, covering key generation, signing, and verification steps.

• Schnorr Digital Signature Scheme: General idea behind the Schnorr digital signature scheme, covering key generation, signing, and verification steps, along with explanations of the required steps.

• Digital Signature Standard (DSS): A standard algorithm for digital signatures, covering key generation and signing/verification.

• ECDSA: A digital signature algorithm based on elliptic curve cryptography, providing key generation, signing and verification.

• Variations: The methods of time-stamping signatures in order to prevent re-use of a signature & blind signatures.

• Entity Authentication: This involves proving the identity of a party or process, whereas message authentication validates the integrity of a message only.

• Verification Categories: Categories for methods in identifying or verifying the authenticity of the sender or entity, such as something known (e.g. a password), something possessed (e.g. an ATM card), and something inherent (e.g. a fingerprint).

• Passwords: Fixed and one-time passwords are traditional methods for entity authentication, relying on something the claimant knows.

• Challenge-Response: Provides authentication using a secret known to the claiming party, without the secret needing to be transmitted.

• Counter with Cipher Block Chaining-Message Authentication Code (CCM): A standard message authentication code (MAC) algorithm.

• Galois/Counter Mode (GCM): A parallelizable message authentication mode, also specified as an internet standard.

• Authenticated Encryption: Methods to protect both confidentiality and authenticity of communications/messages during transmissions. These methods often combine encryption with MAC values.

• Hash Functions: Methods of compressing arbitrary messages to a fixed-size value & its uses (eg. Message Integrity Check, Message Authentication Code, Digital Signatures, Password Verification...).

• Hash function Cryptanalysis Techniques: Various techniques used to find vulnerabilities or weaknesses within a hash function; aimed at finding ways to break security faster than by exhaustive search/brute-force.

• MD5, MD4: Older hash functions that are no longer considered adequately secure. They were common at one point but have since been superseded by more secure methods.

• Security of MACS: A survey of the attacks relevant to breaking various types of MAC algorithms.

• General Characteristics of Hash Functions: A summary of various hash functions (MD5, MD4, SHA-1, SHA-3, SHA-2).

Test your knowledge on cryptographic principles, focusing on hash functions, fingerprints, and message integrity. This quiz covers key concepts such as collision resistance, hash function characteristics, and the Random Oracle Model.