What is a cryptographic hash?
A cryptographic hash function turns any sequence of bytes into a fixed-length digest. The same input produces the same digest, while even a tiny input change should produce a substantially different result.
What hashes are used for
Hashes are commonly used to compare files, confirm a download matches a published checksum, identify cached content, detect accidental changes, and build integrity checks. To verify a file, calculate its digest with the same algorithm and compare every hexadecimal character with the trusted value.
SHA-1, SHA-256, SHA-384, and SHA-512
These names describe members of the Secure Hash Algorithm family and their output lengths. SHA-256 is the most common general-purpose choice here. SHA-384 and SHA-512 provide longer digests. SHA-1 remains useful for compatibility but should not be chosen for new collision-resistant security designs.
Hashing is not encryption or password storage
A digest is not encrypted data and cannot be decrypted. Fast general-purpose SHA hashes are also unsuitable for storing passwords by themselves; password systems should use a deliberately slow, salted password-hashing function.