SHA stands for Secure Hash Algorithm, referring to a type of mathematical function that takes a data input of arbitrary size and condenses it into a data output of fixed size. SHAs are intended to be irreversible, such that it is not possible to generate the function's input simply by knowing its output. Its security is partially dependent on how collision resistant it is, where collision resistance is a probability measurement for two different data inputs to produce the same hash output (i.e. collide with each other).
SHA-256 belongs to the SHA-2 family of hashing algorithms. The '256' denominates the bit-length of the hashing algorithm's data output. SHA-2 is the modern cryptographic standard for online security. Input data can be any sorts of data from one character to entire works of art.
SHA-256 is commonly used to authenticate digital certificates, such as SSL certificates that ensure a secure link between a website and web browsers. SHA-256 is also the cryptographic hash function used for Bitcoin's Proof of Work mining.
Announcing the first SHA1 collision
CWI Amsterdam and Google
Lessons From The History Of Attacks On Secure Hash Functions - Zcash
Documentaries, videos and podcasts
Cryptography: Hash Functions (MIT OpenCourseWare)
March 4, 2016
United States National Institute of Standards and Technology
Walter G. Copan (Director)
United States National Security Agency (NSA)
Paul M. Nakasone (Director)