rtc_stun/
integrity.rs

1#[cfg(test)]
2mod integrity_test;
3
4use crate::attributes::*;
5use crate::checks::*;
6use crate::message::*;
7use shared::error::*;
8
9use md5::{Digest, Md5};
10use ring::hmac;
11use std::fmt;
12
13// separator for credentials.
14pub(crate) const CREDENTIALS_SEP: &str = ":";
15
16// MessageIntegrity represents MESSAGE-INTEGRITY attribute.
17//
18// add_to and Check methods are using zero-allocation version of hmac, see
19// newHMAC function and internal/hmac/pool.go.
20//
21// RFC 5389 Section 15.4
22#[derive(Default, Clone)]
23pub struct MessageIntegrity(pub Vec<u8>);
24
25fn new_hmac(key: &[u8], message: &[u8]) -> Vec<u8> {
26    let mac = hmac::Key::new(hmac::HMAC_SHA1_FOR_LEGACY_USE_ONLY, key);
27    hmac::sign(&mac, message).as_ref().to_vec()
28}
29
30impl fmt::Display for MessageIntegrity {
31    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
32        write!(f, "KEY: 0x{:x?}", self.0)
33    }
34}
35
36impl Setter for MessageIntegrity {
37    // add_to adds MESSAGE-INTEGRITY attribute to message.
38    //
39    // CPU costly, see BenchmarkMessageIntegrity_AddTo.
40    fn add_to(&self, m: &mut Message) -> Result<()> {
41        for a in &m.attributes.0 {
42            // Message should not contain FINGERPRINT attribute
43            // before MESSAGE-INTEGRITY.
44            if a.typ == ATTR_FINGERPRINT {
45                return Err(Error::ErrFingerprintBeforeIntegrity);
46            }
47        }
48        // The text used as input to HMAC is the STUN message,
49        // including the header, up to and including the attribute preceding the
50        // MESSAGE-INTEGRITY attribute.
51        let length = m.length;
52        // Adjusting m.Length to contain MESSAGE-INTEGRITY TLV.
53        m.length += (MESSAGE_INTEGRITY_SIZE + ATTRIBUTE_HEADER_SIZE) as u32;
54        m.write_length(); // writing length to m.Raw
55        let v = new_hmac(&self.0, &m.raw); // calculating HMAC for adjusted m.Raw
56        m.length = length; // changing m.Length back
57
58        m.add(ATTR_MESSAGE_INTEGRITY, &v);
59
60        Ok(())
61    }
62}
63
64pub(crate) const MESSAGE_INTEGRITY_SIZE: usize = 20;
65
66impl MessageIntegrity {
67    // new_long_term_integrity returns new MessageIntegrity with key for long-term
68    // credentials. Password, username, and realm must be SASL-prepared.
69    pub fn new_long_term_integrity(username: String, realm: String, password: String) -> Self {
70        let s = [username, realm, password].join(CREDENTIALS_SEP);
71
72        let mut h = Md5::new();
73        h.update(s.as_bytes());
74
75        MessageIntegrity(h.finalize().as_slice().to_vec())
76    }
77
78    // new_short_term_integrity returns new MessageIntegrity with key for short-term
79    // credentials. Password must be SASL-prepared.
80    pub fn new_short_term_integrity(password: String) -> Self {
81        MessageIntegrity(password.as_bytes().to_vec())
82    }
83
84    // Check checks MESSAGE-INTEGRITY attribute.
85    //
86    // CPU costly, see BenchmarkMessageIntegrity_Check.
87    pub fn check(&self, m: &mut Message) -> Result<()> {
88        let v = m.get(ATTR_MESSAGE_INTEGRITY)?;
89
90        // Adjusting length in header to match m.Raw that was
91        // used when computing HMAC.
92
93        let length = m.length as usize;
94        let mut after_integrity = false;
95        let mut size_reduced = 0;
96
97        for a in &m.attributes.0 {
98            if after_integrity {
99                size_reduced += nearest_padded_value_length(a.length as usize);
100                size_reduced += ATTRIBUTE_HEADER_SIZE;
101            }
102            if a.typ == ATTR_MESSAGE_INTEGRITY {
103                after_integrity = true;
104            }
105        }
106        m.length -= size_reduced as u32;
107        m.write_length();
108        // start_of_hmac should be first byte of integrity attribute.
109        let start_of_hmac = MESSAGE_HEADER_SIZE + m.length as usize
110            - (ATTRIBUTE_HEADER_SIZE + MESSAGE_INTEGRITY_SIZE);
111        let b = &m.raw[..start_of_hmac]; // data before integrity attribute
112        let expected = new_hmac(&self.0, b);
113        m.length = length as u32;
114        m.write_length(); // writing length back
115        check_hmac(&v, &expected)
116    }
117}
rtc_stun/integrity.rs

rtc_stun/
integrity.rs
