File to Double SHA-256.

Double SHA-256, often written SHA-256d or Hash256, is SHA-256 applied to the 32-byte digest of SHA-256. Bitcoin uses it for every block hash, every transaction id, the Merkle tree and the four-byte checksum at the end of a Base58Check address.

Mostly to close the length-extension hole. A single SHA-256 digest lets anyone who knows it continue hashing as if more data followed; hashing the digest again hides the internal state, so the output cannot be extended. Satoshi's design also followed Ferguson and Schneier's advice to double-hash as a conservative margin.

Bitcoin's internal byte order. Block hashes and txids are computed as double SHA-256 and then shown with the bytes reversed, so take the digest from this tool and reverse it two characters at a time to match what an explorer prints.

Not meaningfully. It costs twice the work on a short input and the output is as secure as SHA-256's 128-bit collision resistance. Nobody has found a reason to prefer it outside Bitcoin-derived protocols; for a new system, SHA-256 or SHA3-256 is the plain choice.

Nothing leaves your browser. The file is read on your machine and hashed there, by the browser's Web Crypto API or a WebAssembly build of Double SHA-256 loaded on first use; the page makes no request with its bytes. You can load the page, go offline and keep hashing.

Drop the file onto the pane or choose it with the button. It is read into memory and hashed at once, with no size steps and no upload progress because there is no upload. Files up to 1 GB work; a 100 MB file takes well under a second on Double SHA-256.

Paste the digest the publisher gave you into the Verify field, in hex of either case, with or without spaces, colons or a 0x prefix, or in Base64. The tool says whether it matches the file you dropped. A match means the bytes are exactly the ones that were published.

Hex by default, 64 characters; Base64 and Base64url are one click away and re-encode the same 32 bytes. The download button saves a line in the `digest filename` form that sha256sum-style tools read.

No. The "File to Double SHA-256" tool is free and opens without a sign-in, an account or an install.

Nothing. The "File to Double SHA-256" tool holds your input in the page's memory, so closing or reloading the tab clears it, and it saves nothing in this browser.

The toolbar switches to SHA-256 without leaving the page. Each one reads the same input, so you can compare digests side by side.

Double SHA-256 runs on the browser's own Web Crypto API, so there is nothing to download and it is the fastest path.

No: Double SHA-256 has no keyed form here. Switch to SHA-256 in the toolbar to sign with a key.

Yes: the Double SHA-256 hash generator page has the same algorithms and options and opens on the text box. This page opens on the file pane.

Not on its own. Double SHA-256 is built to be fast, and fast hashes are cheap for an attacker to guess against. Passwords need a salted, deliberately slow hash: use Argon2id, Argon2d, and bcrypt from the hash generators, which draw a fresh random salt each time.

Closest to the "File to Double SHA-256" tool: Double SHA-256 hash generator, SHA-256 hash generator, RIPEMD-160 hash generator, Keccak-256 hash generator. Each opens on its own page, free and in the browser.

The "File to Double SHA-256" tool is one of 64 in its group. The group's page, /tools/hash, lists them all.

The tool is free. Its interface is built from shadcn.io's own components (Button, Input, Slider and the rest of the registry under /ui), which come in React, Vue, Svelte and Solid. Pro adds the blocks and templates for the product around it.