# crypto.sha256

`sha256(utf8Encode("abc"))` is the 32 bytes
`ba7816bf8f01cfea414140de5dae2223b00361a396177a9cb410ff61f20015ad` (print them
with `hexEncode`). This is SHA-256 exactly as FIPS 180-4 defines it.

Bytes in and out are lists of integers 0 to 255, as everywhere in the registry
(see `encoding.hex`); hash text by encoding it with `encoding.utf8` first, so
all three languages hash the same bytes.

The TypeScript implementation is plain code with no `node:crypto` and no
`crypto.subtle`, so it runs unchanged in a browser, in Node and in a worker,
synchronously (`crypto.subtle.digest` is asynchronous and only exists in
secure contexts). The Python implementation uses the standard library's
`hashlib`, and the Rust one is written out with the standard library only.
All three are checked against the same vectors.

A hash is not a password hash: a single SHA-256 of a password can be guessed
billions of times a second. Store passwords with `auth.password-hash`, which
uses PBKDF2 with a salt and many iterations. A hash is not a MAC either: to
prove a message came from someone holding a key, use `crypto.hmac-sha256`
(prefixing the key and hashing is open to length extension).

The digests in the vectors are the published ones: "abc" and the 448-bit
message from the NIST example values for FIPS 180-4 (SHA256.pdf), the empty
string, the pangram, and messages of 55, 56, 64 and 119 bytes, which sit on
either side of the points where the padding needs a second block.

Source: FIPS 180-4, Secure Hash Standard, section 6.2
(https://csrc.nist.gov/pubs/fips/180-4/upd1/final) and the NIST
cryptographic standards example values
(https://csrc.nist.gov/projects/cryptographic-standards-and-guidelines/example-values).