Hashing
Also known as: hash function, hash value, checksum, SHA-256
Hashing turns any input into a fixed-length string of characters using a one-way function — you cannot reverse a hash back into the original data. It is used to store passwords safely, verify files have not changed, and detect duplicates.
- One-way: a hash cannot be reversed to the input
- Same input always yields the same fixed-length hash
- Used for passwords, file integrity, and duplicate detection
Hashing vs encryption
The key difference is reversibility. Encryption is two-way: with the key you can get the original data back. Hashing is one-way — the same input always produces the same hash, but there is no key to turn the hash back into the input.
A good hash function spreads results so even a one-character change produces a completely different hash. Common algorithms include the SHA-2 family (such as SHA-256). Older ones like MD5 and SHA-1 are now considered weak for security use.
Where you encounter it
Services store a hash of your password rather than the password itself, so a leaked database does not directly expose it. File downloads publish a checksum so you can confirm the file arrived intact. Photo cleaners and backup tools hash files to spot exact duplicates quickly without comparing every byte.
Because hashes are deterministic, identical files share an identical hash — which is exactly how duplicate detection finds copies of the same image.