rustls/crypto/
hmac.rs

1use alloc::boxed::Box;
2
3use zeroize::Zeroize;
4
5/// A concrete HMAC implementation, for a single cryptographic hash function.
6///
7/// You should have one object that implements this trait for HMAC-SHA256, another
8/// for HMAC-SHA384, etc.
9pub trait Hmac: Send + Sync {
10    /// Prepare to use `key` as a HMAC key.
11    fn with_key(&self, key: &[u8]) -> Box<dyn Key>;
12
13    /// Give the length of the underlying hash function.  In RFC2104 terminology this is `L`.
14    fn hash_output_len(&self) -> usize;
15}
16
17/// A HMAC tag, stored as a value.
18#[derive(Clone)]
19pub struct Tag {
20    buf: [u8; Self::MAX_LEN],
21    used: usize,
22}
23
24impl Tag {
25    /// Build a tag by copying a byte slice.
26    ///
27    /// The slice can be up to [`Tag::MAX_LEN`] bytes in length.
28    pub fn new(bytes: &[u8]) -> Self {
29        let mut tag = Self {
30            buf: [0u8; Self::MAX_LEN],
31            used: bytes.len(),
32        };
33        tag.buf[..bytes.len()].copy_from_slice(bytes);
34        tag
35    }
36
37    /// Maximum supported HMAC tag size: supports up to SHA512.
38    pub const MAX_LEN: usize = 64;
39}
40
41impl Drop for Tag {
42    fn drop(&mut self) {
43        self.buf.zeroize();
44    }
45}
46
47impl AsRef<[u8]> for Tag {
48    fn as_ref(&self) -> &[u8] {
49        &self.buf[..self.used]
50    }
51}
52
53/// A HMAC key that is ready for use.
54///
55/// The algorithm used is implicit in the `Hmac` object that produced the key.
56pub trait Key: Send + Sync {
57    /// Calculates a tag over `data` -- a slice of byte slices.
58    fn sign(&self, data: &[&[u8]]) -> Tag {
59        self.sign_concat(&[], data, &[])
60    }
61
62    /// Calculates a tag over the concatenation of `first`, the items in `middle`, and `last`.
63    fn sign_concat(&self, first: &[u8], middle: &[&[u8]], last: &[u8]) -> Tag;
64
65    /// Returns the length of the tag returned by a computation using
66    /// this key.
67    fn tag_len(&self) -> usize;
68}
rustls/crypto/hmac.rs

rustls/crypto/
hmac.rs
