rustls/crypto/hmac.rs
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use alloc::boxed::Box;
use zeroize::Zeroize;
/// A concrete HMAC implementation, for a single cryptographic hash function.
///
/// You should have one object that implements this trait for HMAC-SHA256, another
/// for HMAC-SHA384, etc.
pub trait Hmac: Send + Sync {
/// Prepare to use `key` as a HMAC key.
fn with_key(&self, key: &[u8]) -> Box<dyn Key>;
/// Give the length of the underlying hash function. In RFC2104 terminology this is `L`.
fn hash_output_len(&self) -> usize;
}
/// A HMAC tag, stored as a value.
#[derive(Clone)]
pub struct Tag {
buf: [u8; Self::MAX_LEN],
used: usize,
}
impl Tag {
/// Build a tag by copying a byte slice.
///
/// The slice can be up to [`Tag::MAX_LEN`] bytes in length.
pub fn new(bytes: &[u8]) -> Self {
let mut tag = Self {
buf: [0u8; Self::MAX_LEN],
used: bytes.len(),
};
tag.buf[..bytes.len()].copy_from_slice(bytes);
tag
}
/// Maximum supported HMAC tag size: supports up to SHA512.
pub const MAX_LEN: usize = 64;
}
impl Drop for Tag {
fn drop(&mut self) {
self.buf.zeroize();
}
}
impl AsRef<[u8]> for Tag {
fn as_ref(&self) -> &[u8] {
&self.buf[..self.used]
}
}
/// A HMAC key that is ready for use.
///
/// The algorithm used is implicit in the `Hmac` object that produced the key.
pub trait Key: Send + Sync {
/// Calculates a tag over `data` -- a slice of byte slices.
fn sign(&self, data: &[&[u8]]) -> Tag {
self.sign_concat(&[], data, &[])
}
/// Calculates a tag over the concatenation of `first`, the items in `middle`, and `last`.
fn sign_concat(&self, first: &[u8], middle: &[&[u8]], last: &[u8]) -> Tag;
/// Returns the length of the tag returned by a computation using
/// this key.
fn tag_len(&self) -> usize;
}