MD5 vs SHA-256: What Hashes Are and When to Use Which

A hash function takes any input, a password, a file, a sentence, and produces a short fixed length fingerprint for it. The same input always produces the same fingerprint, and changing even one letter of the input produces a completely different one. That is the whole idea, and it powers everything from download verification to password storage.

The fingerprint is one way. You can go from data to hash instantly, but you cannot run a hash backward to recover the original data. That property is what makes the security uses possible, and it is also where MD5 and SHA-256 part ways.

What went wrong with MD5

MD5 dates from 1992, and researchers have since broken its core promise. It is now practical to create two different inputs that produce the same MD5 fingerprint, which is called a collision. Once collisions are cheap to make, an attacker can forge data that passes an MD5 check, so the fingerprint can no longer be trusted to prove what something is. For that reason MD5 is considered broken for any security purpose: no certificates, no signatures, and absolutely no password storage.

MD5 still appears in the wild for non security jobs, such as quick checksums to detect accidental corruption and cache keys inside applications, where nobody is attacking anything and speed is the only concern. Try it yourself with the MD5 Hash Generator to see what its output looks like.

Why SHA-256 is the current standard

SHA-256 belongs to the SHA-2 family and produces a 256 bit fingerprint with no practical collision attacks known. It is what modern systems actually use: website certificates, software download verification, code signing, and blockchain systems all rest on it. When a security standard, an API, or an auditor asks for a hash today, SHA-256 is the expected answer. You can generate one instantly with the SHA256 Hash tool.

The simple decision rule

Does anything depend on this hash being trustworthy against a person who might cheat? Then use SHA-256, no exceptions. Is it a purely internal convenience, like deduplicating files on your own machine? MD5 will not hurt, but SHA-256 costs almost nothing extra, so most engineers simply use it everywhere and stop thinking about it.

One note on passwords: storing passwords properly uses special slow algorithms such as bcrypt or Argon2, not a bare fast hash of either kind. Fast hashes, even SHA-256, can be guessed against at enormous speed, which is exactly what you do not want for passwords.

The bottom line

Hashes are fingerprints. MD5 is a broken fingerprint that survives only in casual, non security jobs. SHA-256 is the working standard. When in doubt, SHA-256.