SHA stands for secure hash algorithm. SHA-256 is a hash function (https://csrc.nist.gov/Projects/Hash-Functions) derivative of the SHA-2 family. The significance of offering SHA-256 support is based on the difference between the SHA-1, which MongoDB supports, and SHA-2 families of hash algorithms. SHA-1, introduced in 1995, used algorithms similar to an older family of hash functions: MD2, MD4, and MD5. SHA-1, however, produces a hash value of 160 bits compared with 128 for the MDx series. SHA-256, introduced in 2012, increases the hash value size to 256, which makes it exponentially more difficult to crack. Attack vectors that could compromise communications based upon SHA-1 and SHA-2 include the preimage attack, the collision attack, and the length-extension attack.
The first attack relies upon brute-force attack methods to reverse the hash. In the past, this required computational power beyond the reach of anyone other than a well-funded organization (for example...
