Question 1

Why is MD5 included if it's not considered secure anymore?

Accepted Answer

MD5 is no longer safe for security purposes like password storage, but it's still widely used for non-security checksums — like verifying a file downloaded correctly — so it's included for that practical use case.

Question 2

Which hash should I use for security-sensitive purposes?

Accepted Answer

SHA-256 or higher (SHA-384, SHA-512) are the current standards for security-sensitive hashing — avoid MD5 and SHA-1 for anything security-related, since both have known weaknesses.

Question 3

Why does the same input always produce the same hash?

Accepted Answer

Hash functions are deterministic — identical input always produces identical output, which is exactly what makes them useful for verifying that data hasn't changed.

Question 4

Can I reverse a hash back into the original text?

Accepted Answer

No — cryptographic hashes are one-way by design. The "verify against a known hash" feature works by hashing your input again and comparing the result, not by decoding the hash itself.

Question 5

Can I hash a file instead of typed text?

Accepted Answer

Yes — switch the source to "File" and drop in anything up to 25 MB. This is the classic use for a checksum: comparing the hash of a downloaded file against the one the publisher listed to confirm it wasn't corrupted or tampered with in transit.

Question 6

What does the "legacy" tag on MD5 and SHA-1 mean?

Accepted Answer

Both have known collision attacks — it's practical to construct two different inputs that produce the same hash, which breaks the guarantees needed for security use like signatures or password storage. They're still fine for non-adversarial checksums (catching accidental corruption), just not for anything where someone might deliberately try to fake a match.

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