dQicCRfR

1pub struct Hkdf {
2  pub salt: Vec<u8>,
3  pub data: Vec<u8>,
4  pub info: Vec<u8>,
5  pub hmac: usize,
6  pub length: usize,
7}
8
9impl Drop for Hkdf {
10  fn drop(&mut self) {
11    //println!("DROPPING");
12    self.salt.clear();
13    self.data.clear();
14    self.info.clear()
15  }
16}
17
18impl Hkdf {
19  /// Return HMAC matching argument passsed to Hkdf.
20  pub fn hkdf_extract(&self, data: &[u8], salt: &[u8]) -> Vec<u8> {
21    let hmac_res = Hmac {
22        secret_key: salt.to_vec(),
23        message: data.to_vec(),
24        sha2: self.hmac
25    };
26
27    hmac_res.hmac_compute()
28  }
29
30  /// The HKDF Expand step. Returns an HKDF.
31  pub fn hkdf_compute(&self) -> Vec<u8> {
32    // Check that the selected key length is within the limit.
33    if self.length as f32 > 255_f32 * (self.hmac / 8) as f32 {
34        panic!("Derived key length above max. 255 * (HMAC OUTPUT LENGTH IN BYTES)");
35    }
36
37    let n_iter = (self.length as f32 / (self.hmac / 8) as f32).ceil() as usize;
38
39    let mut con_step: Vec<u8> = vec![];
40    let mut t_step: Vec<u8> = vec![];
41    let mut hkdf_final: Vec<u8> = vec![];
42
43    for x in 1..n_iter+1 {
44            con_step.append(&mut t_step);
45            con_step.extend_from_slice(&self.info);
46            con_step.push(x as u8);
47            t_step.extend_from_slice(&self.hkdf_extract(
48                &con_step,
49                &self.hkdf_extract(&self.data, &self.salt))
50            );
51            con_step.clear();
52
53            hkdf_final.extend_from_slice(&t_step);
54    }
55
56    hkdf_final.truncate(self.length);
57
58    hkdf_final
59  }
60}
61	
62#[inline(never)]
63/// Comparison in constant time.
64pub fn compare_ct(x: &[u8], y: &[u8]) -> bool {
65
66  let length = x.len();
67
68  if length != y.len() {
69    false;
70  }
71
72  let mut result: u8 = 0;
73
74  for n in 0..length {
75    result |= x[n] ^ y[n];
76  }
77
78  result == 0
79}