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Cryptographic Hash Functions (CHF) (Characteristics (Infeasible to…
Cryptographic Hash Functions (CHF)
Hash Function
Function that can be used to map data of arbitrary size to fixed size values.
Values returned are called hash values, hash codes, digests or hashes
Values are used to index a fixed size table called a hash table.
Used in cryptography. One way function practically infeasible to invert
Algorithms
SHA-1
Applications: Previously used for security such as TLS , SSL, now discontinued. Now used for data integrity for e.g. Git
Vulnerabilities: Collision attack
Digest size: 160 bit or 40 hex digits
SHA-2
Applications: Security - TLS, SSL. DKIM message signing standard, Cryptocurrencies use it to for calculating proof of work
Vulnerabilities: ?
Digest Sizes: 224, 256, 384 or 512 bits, i.e. 56, 64, 96, 128 hex digits
MD5
Applications: checksum and data integrity checks
Vulnerabilities: Collision attack
Digest Size: 128 bit or 32 hex digits
SHA-3
Digest Size: varies
Characteristics
Infeasible to generate a message that yields a given hash value (i.e. cannot reproduce by guessing)
Infeasible to find two different messages with same hash value
Quick to compute hash value of any message
Small change to message should change the hash value significantly - avalanche effect
Deterministic - same message results in same hash
Applications
Password verification - store hash of original password and compare with hash of provided password
Proof-of-work: Deter denial of service attacks by requiring requestor to do some work
Signature generation and verification
File or data identifier - e.g. Git
Verify integrity of messages and files: Generate hash of message or file and compare after transmission