Question 1

What is a hash function?

Accepted Answer

A hash function takes an input of any size and produces a fixed-size output (the hash). The same input always produces the same hash, but even a tiny change in the input creates a completely different output. Good hash functions make it infeasible to find the original input from the hash alone.

Question 2

Which hash algorithm should I use?

Accepted Answer

For security-sensitive uses (password hashing, digital signatures, integrity checks), use SHA-256 or SHA-512. SHA-1 and MD5 are considered broken for security but are still useful for checksums, caching keys, and non-security uses. Never use MD5 or SHA-1 for new security systems.

Question 3

Is MD5 still safe to use?

Accepted Answer

MD5 is not cryptographically secure — collisions can be found in seconds. It is still widely used for non-security purposes like cache keys, ETags, and file deduplication, but should never be used for digital signatures, password storage, or integrity verification against a motivated attacker.

Question 4

Is my input sent to a server?

Accepted Answer

No. All hashes are computed locally in your browser using the Web Crypto API (for SHA) and a pure-JavaScript implementation (for MD5). Your input never leaves your device.

Question 5

Why are the SHA-1 and SHA-256 hashes so different for the same input?

Accepted Answer

Different algorithms use different internal operations, block sizes, and output sizes. SHA-1 produces a 160-bit (40-hex-character) hash, while SHA-256 produces a 256-bit (64-hex-character) hash. They are designed to be independent — knowing one tells you nothing about the other.

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