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 /// Return `true` if this is backed by a FIPS-approved implementation.
17 fn fips(&self) -> bool {
18 false
19 }
20}
21
22/// A HMAC tag, stored as a value.
23#[derive(Clone)]
24pub struct Tag {
25 buf: [u8; Self::MAX_LEN],
26 used: usize,
27}
28
29impl Tag {
30 /// Build a tag by copying a byte slice.
31 ///
32 /// The slice can be up to [`Tag::MAX_LEN`] bytes in length.
33 pub fn new(bytes: &[u8]) -> Self {
34 let mut tag: Tag = Self {
35 buf: [0u8; Self::MAX_LEN],
36 used: bytes.len(),
37 };
38 tag.buf[..bytes.len()].copy_from_slice(src:bytes);
39 tag
40 }
41
42 /// Maximum supported HMAC tag size: supports up to SHA512.
43 pub const MAX_LEN: usize = 64;
44}
45
46impl Drop for Tag {
47 fn drop(&mut self) {
48 self.buf.zeroize();
49 }
50}
51
52impl AsRef<[u8]> for Tag {
53 fn as_ref(&self) -> &[u8] {
54 &self.buf[..self.used]
55 }
56}
57
58/// A HMAC key that is ready for use.
59///
60/// The algorithm used is implicit in the `Hmac` object that produced the key.
61pub trait Key: Send + Sync {
62 /// Calculates a tag over `data` -- a slice of byte slices.
63 fn sign(&self, data: &[&[u8]]) -> Tag {
64 self.sign_concat(&[], middle:data, &[])
65 }
66
67 /// Calculates a tag over the concatenation of `first`, the items in `middle`, and `last`.
68 fn sign_concat(&self, first: &[u8], middle: &[&[u8]], last: &[u8]) -> Tag;
69
70 /// Returns the length of the tag returned by a computation using
71 /// this key.
72 fn tag_len(&self) -> usize;
73}
74