Question 1

What is a hash function, in one paragraph?

Accepted Answer

A cryptographic hash is a deterministic function that turns any input — a string, a file, a 10 GB tarball — into a fixed-size digest of bytes. Two properties matter: the same input always produces the same digest, and finding two different inputs with the same digest should be computationally infeasible. MD5 produces 128-bit digests, SHA-1 160-bit, SHA-256 256-bit, SHA-384 384-bit, and SHA-512 512-bit. The longer the digest, the more bits of collision resistance you get — assuming the algorithm itself hasn't been broken.

Question 2

Is MD5 still safe to use?

Accepted Answer

Not for anything security-sensitive. Wang and Yu published practical MD5 collisions in 2005, and chosen-prefix attacks soon followed; the Flame malware (2012) used one to forge a Microsoft code-signing certificate. Don't use MD5 for digital signatures, certificate authorities, password hashing, or content addressing where adversaries can choose the input. MD5 is still fine as a non-cryptographic checksum to detect accidental corruption — for example, the 'md5sum' line in a download mirror — but treat that line as a checksum, not a guarantee.

Question 3

What about SHA-1?

Accepted Answer

SHA-1 is broken for collision-resistance: Google and CWI demonstrated the first practical chosen-prefix collision (the 'SHAttered' PDFs) in 2017, and a fully chosen-prefix attack was shown in 2020. NIST deprecated SHA-1 for digital signatures in 2011 and announced full retirement by 2030. SHA-1 still appears in some interop contexts (HMAC-SHA-1 with random keys is unaffected; old TLS suites; the SHA-1 of a Git commit), but new code should use SHA-256 or stronger.

Question 4

Does this tool send my text or files to a server?

Accepted Answer

No. The text input, file contents, and HMAC secret are all hashed in your browser tab. Open DevTools' Network tab while you hash and you'll see it stay silent. SHA-1, SHA-256, SHA-384, and SHA-512 use the browser's built-in W3C SubtleCrypto API (the same primitive Node's 'node:crypto' wraps); MD5 — which SubtleCrypto deliberately omits — uses a pure-JavaScript implementation on this page that matches RFC 1321 Appendix A.5 byte-for-byte. Files larger than 50 MiB are rejected client-side without reading them.

Question 5

How is HMAC different from a plain hash?

Accepted Answer

HMAC (RFC 2104) is keyed message authentication. Plain SHA-256(message) lets anyone with the bytes recompute the digest; HMAC-SHA-256(key, message) lets you prove the message came from someone holding the shared key, since recomputing the digest requires the key. The construction is H((key XOR opad) || H((key XOR ipad) || message)), where ipad = 0x36 and opad = 0x5c repeated to the hash's block size. The math is independent of the hash, so swapping SHA-256 for SHA-512 or MD5 just swaps the inner primitive; the API on this page exposes HMAC for every algorithm.

Question 6

Why are my hex digest and the openssl output different?

Accepted Answer

Most of the time, one of three things: the input had a trailing newline that you didn't notice ('echo -n' vs 'echo'), the file had a UTF-8 BOM or CRLF line endings that this tool's UTF-8 input does not, or the openssl invocation used a different algorithm or HMAC variant. Drop the file into the File tab here and compare byte counts — if the byte count matches, the digest will match. 'printf '%s' "abc" | openssl dgst -sha256' and the 'abc' sample here produce the same hex.

Question 7

What's the difference between SHA-256, SHA-384 and SHA-512?

Accepted Answer

All three are SHA-2 family hashes specified in FIPS 180-4. SHA-256 processes 32-bit words in 64 rounds and outputs 256 bits; SHA-512 processes 64-bit words in 80 rounds and outputs 512 bits. SHA-384 is SHA-512 with different initial values and the output truncated to 384 bits — it exists mostly so 64-bit-native systems can use SHA-512's faster round function while paying for only 384 bits of digest. On 64-bit hardware SHA-512 is often faster than SHA-256; on 32-bit hardware, the reverse.

Question 8

Should I use SHA-256 or bcrypt for passwords?

Accepted Answer

bcrypt, scrypt, or Argon2 — not a plain hash. A single SHA-256 takes microseconds, so an attacker who steals your hash database can try billions of guesses per second on a GPU. Password hashing functions are deliberately slow and memory-hard, raising the cost per guess by orders of magnitude. Use Argon2id with a per-user salt and tuned cost parameters; if you're on a stack that doesn't ship Argon2, bcrypt with a work factor of 12 or higher is the long-standing fallback.

Question 9

What encoding should I pick — hex, base64, or base64url?

Accepted Answer

Hex (the default) is the most common form you'll see in command-line tools, Git, X.509 fingerprints, and 'md5sum' output. Base64 packs more entropy per character (every 3 bytes become 4 chars instead of 6), which matters for cookies, JWT signatures, and HTTP headers. Base64url replaces '+' with '-' and '/' with '_' and drops the '=' padding so the digest is safe to use directly in URLs. The underlying bytes are identical — only the human-readable shell changes.

Question 10

Can I hash very large files here?

Accepted Answer

The page caps file input at 50 MiB. SubtleCrypto.digest reads the whole buffer in one call, so the practical limit is your device's available memory; the cap is set conservatively so users on phones never see a tab crash. For files larger than that, run 'sha256sum file' locally on Linux/macOS or 'certutil -hashfile file SHA256' on Windows — both ship with the OS and use the same FIPS 180-4 algorithms, so the digest matches this page's exactly.

MD5 & SHA Hash Generator — in-browser, no upload

HMAC (keyed hashing)

How it works

Worked examples

Frequently asked questions

Sources & references

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