The Hash Function Dr. Ron Eaglin.

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Presentation transcript:

The Hash Function Dr. Ron Eaglin

What is a hash function? At its core… A hash function is any function that can be used to map data of arbitrary size to data of fixed size.

Really?! A B C D E

Why would this be important?….

Applications of Hash Functions Rapid Data Lookup Hash functions are primarily used in hash tables to quickly locate a data record (e.g., a dictionary definition) given its search key (the headword). Specifically, the hash function is used to map the search key to an index; the index gives the place in the hash table where the corresponding record should be stored.

Applications of Hash Functions Finding Duplicate Records Duplicates can then be found by scanning every bucket which contains two or more members, fetching those records, and comparing them. Faster than comparing all records to each other. Also good for finding similar records….

Applications of Hash Functions Password Security Instead of storing passwords in a table – the hashed value is stored instead. The user entered value is hashed and compared against the value stored. The original password is never stored anywhere – more secure.

Applications of Hash Functions Cryptography Some standard applications that employ hash functions include authentication, message integrity (using an HMAC (Hashed MAC)), message fingerprinting, data corruption detection, and digital signature efficiency.

Properties of Hash Functions Deterministic Same input will always give the same output

Properties of Hash Functions Uniformity Maps all inputs evenly over the range of output.

Properties of Hash Functions Definable Range The function has a discrete and definable range of outputs.

Properties of Hash Functions Non-Invertable Cannot take hashed value and go back to the original key – one way function.

Some Hash Functions MD5 - https://en.wikipedia.org/wiki/MD5 Zobrist - https://en.wikipedia.org/wiki/Zobrist_hashing Blake - https://en.wikipedia.org/wiki/BLAKE_(hash_function) Grøstl - https://en.wikipedia.org/wiki/Gr%C3%B8stl And many many more….