# Hash Strings

Certain zb functions take a *{index}`hash string`* argument.
Hash strings are the result of a [cryptographic hash function][]
and are used to ensure integrity of an output.
Hash strings are either in the format `<type>:<base16|base32|base64>`
or the [Subresource Integrity hash expression][] format `<type>-<base64>`,
where `<type>` is one of `md5`, `sha1`, `sha256`, or `sha512`.

Examples include:

- `sha256:ee4c78f4b1915c7dafb0d55e8cd6f20fe82396a21a6ab2add9bb879fb9301bc2`
- `sha1:da39a3ee5e6b4b0d3255bfef95601890afd80709`
- `sha256-7kx49LGRXH2vsNVejNbyD+gjlqIaarKt2buHn7kwG8I=`

[cryptographic hash function]: https://en.wikipedia.org/wiki/Cryptographic_hash_function
[Subresource Integrity hash expression]: https://www.w3.org/TR/SRI/#the-integrity-attribute