Cryptography that never leaves your browser

Hashing, verification, encryption and key handling done on your own machine, using the cryptographic implementation already built into your browser. Nothing here invents a cipher, and nothing here uploads what you give it.

Home › Cryptography & Security

Processed locally in your browser Files, passwords, keys and text stay on your device. There is no upload step, no server that could receive them, and no analytics event on any of these pages is permitted to carry a value you typed.

Verify and authenticate

Check that a file is the file it is supposed to be.

File Hash CalculatorSHA-256, SHA-384 or SHA-512 of any file, calculated in your browser. Nothing uploaded, and the filename never leaves the page.SHA-2 Checksum VerifierPaste the digest a publisher listed and find out whether your copy matches. Whitespace and case forgiven; a wrong length is not.Match / no match File ComparatorAre two files byte-for-byte identical? Sizes first, then SHA-256 of each. Neither file is uploaded.

Generate

Values that need to be unguessable, drawn properly.

Password GeneratorUnbiased selection from your browser's CSPRNG, with the entropy counted from the real number of possibilities — including what each option costs.Honest entropy Passphrase GeneratorIndependently chosen random words, with the actual list size and bits per word shown rather than borrowed from somebody else's list. Secure Random GeneratorBytes, hex, Base64url, Base32, UUIDs and bounded whole numbers. Ranges use rejection sampling, so no value is quietly more likely.Unbiased

Encrypt

Make something unreadable to everyone without the password.

File EncryptionAES-256-GCM with a key derived from your password, performed by your browser. Fresh salt and nonce every time, and a documented container format.Flagship Text EncryptionThe same container, wrapped so it survives being pasted through chat or email. Base64url, and forgiving about how it arrives.

Authenticate and sign

Establish that something came from who you think, and has not changed.

Digital SignaturesSign text or a file with a private key, or verify against a public one. ECDSA, Ed25519 and RSA, all via Web Crypto. HMAC Generator and VerifierA tag only someone with the shared key can produce. Tested against RFC 4231, including the long-key case implementations get wrong.RFC 4231 Key Pair GeneratorGenerate a signing key pair locally, exported as PEM and verified end to end before you are handed it. Public Key InspectorAlgorithm, curve or modulus size, encoding and fingerprint — read from the bytes, with private keys refused.

Certificates

Read what a certificate says. Deciding whether to believe it is a different job.

X.509 Certificate InspectorSubject, issuer, validity, alternative names, key and extensions. Fingerprint matches OpenSSL's; parsing and trusting kept firmly apart.Parses, never validates PEM / DER ConverterThe same bytes in two wrappings, passed through unchanged. Format re-encodings are refused rather than attempted.

Developer tools

The formats that turn up in an authentication flow.

JWT Decoder and VerifierRead a token's claims, or check its signature against a key you supply. The algorithm is yours to choose and alg:none is refused outright.No alg confusion TOTP Generator and InspectorThe current code from a seed you own, with the countdown and the neighbouring codes for when clocks disagree. RFC 6238.RFC 6238

Convert and inspect

Move data between representations, and understand what you are looking at.

UUID GeneratorVersion 4 identifiers from your browser's own generator, with the structure explained — including why it is 122 random bits and not 128. Encoding ConverterText, hex, binary, Base64, Base64url, Base32 and percent-encoding. Unicode through UTF-8, malformed input refused with a reason.Not encryption

Learn how it works

Educational tools. Nothing in this group protects anything, and each says so.

Classical Cipher PlaygroundCaesar, Atbash, Affine, Vigenère and two transpositions, shown letter by letter — then broken in front of you.Educational only Hash Avalanche VisualizerChange one character and watch about half a SHA-256 digest flip, with an honest account of why it is never exactly half. Entropy ExplorerWhat a bit of entropy is, worked out for characters, words, dice and bytes — and the length-versus-complexity question done properly. Public-Key VisualizerA real ECDSA signature made and checked step by step, then broken two ways. Built around what signing does and does not establish.Real keys Cipher Puzzle SheetsPrintable classical-cipher puzzles at three difficulties, with answer keys on their own page.

The rule these tools are built on

Nothing here implements a cryptographic primitive. Every hash, cipher, key derivation and random number comes from Web Crypto — the implementation already in your browser, written and reviewed by the people who wrote your browser. The shared module behind these pages is a documented adapter over it and nothing more.

That boundary is not fussiness. Cryptographic mistakes are unusual in that they produce output which looks entirely correct: the ciphertext is random-looking, the digest is the right length, the round trip works, and the thing is broken anyway. Ordinary testing does not find them. The only reliable defence available to a project this size is to not write the primitive.

Three things the shared module does implement, none of them cryptographic: the RFC 4648 encodings, the byte layout of the encrypted container, and unbiased selection from random bytes. All three are checked against published test vectors or measured distributions.

Tested against published answers, not against itself

A round trip proves only that the code agrees with nobody but itself, which for cryptography is precisely the failure mode. So where a standards body publishes known answers, those are what the engine is checked against: FIPS 180-4 for the SHA family, RFC 4231 for HMAC, RFC 6070 for PBKDF2, the GCM specification's own cases for AES-GCM, and RFC 4648's vectors for Base64 and Base32.

Where no official vectors exist — PBKDF2 with SHA-256, for instance — the engine is checked against an independent implementation instead.

Language you will not find here

Not "military grade", not "unhackable", not "100% secure". None of those describes anything a person could verify. What is written instead is which standard is in use, which implementation performs it, what has been tested, and where the limits are — including the ones that are inconvenient to mention.

The password generator says that requiring one of every character type makes a password weaker. The checksum verifier says that a matching digest published beside the download proves very little. The file hash tool says why very large files fail rather than pretending they do not. That is the tone throughout, and where a tool cannot do something safely it says so instead of doing it badly.

What is not here yet

This category is being built out in phases. Encryption of files and text, digital signatures, HMAC, key generation and inspection, certificate and JWT tools, TOTP, secret sharing and a set of teaching tools for classical ciphers are all specified and coming.

Three of them are waiting on a decision rather than on work: password strength estimation, OpenPGP, and Shamir secret sharing all need a substantial reviewed library, and this site has no build step and does not load code from a CDN. Writing any of those from scratch would break the one rule the whole category rests on.