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# RustCrypto: Digest Algorithm Traits
[![crate][crate-image]][crate-link]
[![Docs][docs-image]][docs-link]
![Apache2/MIT licensed][license-image]
![Rust Version][rustc-image]
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[![Build Status][build-image]][build-link]
Traits which describe functionality of [cryptographic hash functions][0], a.k.a.
digest algorithms.
See [RustCrypto/hashes][1] for implementations which use this trait.
[Documentation][docs-link]
## Minimum Supported Rust Version
Rust **1.41** or higher.
Minimum supported Rust version can be changed in the future, but it will be
done with a minor version bump.
## SemVer Policy
- All on-by-default features of this library are covered by SemVer
- MSRV is considered exempt from SemVer as noted above
## Usage
Let us demonstrate how to use crates in this repository using Sha256 as an
example.
First add the `sha2` crate to your `Cargo.toml`:
```toml
[dependencies]
sha2 = "0.10"
```
`sha2` and other crates re-export `digest` crate and `Digest` trait for
convenience, so you don't have to add `digest` crate as an explicit dependency.
Now you can write the following code:
```rust
use sha2::{Sha256, Digest};
let mut hasher = Sha256::new();
let data = b"Hello world!";
hasher.update(data);
// `input` can be called repeatedly and is generic over `AsRef<[u8]>`
hasher.update("String data");
// Note that calling `finalize()` consumes hasher
let hash = hasher.finalize();
println!("Result: {:x}", hash);
```
In this example `hash` has type [`GenericArray<u8, U64>`][2], which is a generic
alternative to `[u8; 64]`.
Alternatively you can use chained approach, which is equivalent to the previous
example:
```rust
let hash = Sha256::new()
.chain_update(b"Hello world!")
.chain_update("String data")
.finalize();
println!("Result: {:x}", hash);
```
If the whole message is available you also can use convenience `digest` method:
```rust
let hash = Sha256::digest(b"my message");
println!("Result: {:x}", hash);
```
### Hashing `Read`-able objects
If you want to hash data from [`Read`][3] trait (e.g. from file) you can rely on
implementation of [`Write`][4] trait (requires enabled-by-default `std` feature):
```rust
use sha2::{Sha256, Digest};
use std::{fs, io};
let mut file = fs::File::open(&path)?;
let mut hasher = Sha256::new();
let n = io::copy(&mut file, &mut hasher)?;
let hash = hasher.finalize();
println!("Path: {}", path);
println!("Bytes processed: {}", n);
println!("Hash value: {:x}", hash);
```
### Generic code
You can write generic code over `Digest` (or other traits from `digest` crate)
trait which will work over different hash functions:
```rust
use digest::Digest;
// Toy example, do not use it in practice!
fn hash_password<D: Digest>(password: &str, salt: &str, output: &mut [u8]) {
let mut hasher = D::new();
hasher.update(password.as_bytes());
hasher.update(b"$");
hasher.update(salt.as_bytes());
output.copy_from_slice(hasher.finalize().as_slice())
}
let mut buf1 = [0u8; 32];
let mut buf2 = [0u8; 64];
hash_password::<sha2::Sha256>("my_password", "abcd", &mut buf1);
hash_password::<sha2::Sha512>("my_password", "abcd", &mut buf2);
```
If you want to use hash functions with trait objects, use `digest::DynDigest`
trait.
## License
Licensed under either of:
at your option.
### Contribution
Unless you explicitly state otherwise, any contribution intentionally submitted
for inclusion in the work by you, as defined in the Apache-2.0 license, shall be
dual licensed as above, without any additional terms or conditions.
[//]: # (badges)
[build-image]: https://github.com/RustCrypto/traits/workflows/digest/badge.svg?branch=master&event=push
[//]: # (general links)