rtc_stun/
integrity.rs

1#[cfg(test)]
2mod integrity_test;
3
4use crate::attributes::*;
5use crate::checks::*;
6use crate::message::*;
7use md5::{Digest, Md5};
8use shared::error::*;
9
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)]
23/// The `MESSAGE-INTEGRITY` key: an HMAC-SHA1 is computed over the message with it.
24///
25/// Built from a short-term password, or from a long-term username/realm/password triple.
26pub struct MessageIntegrity(pub Vec<u8>);
27
28fn new_hmac(key: &[u8], message: &[u8]) -> Vec<u8> {
29    let mac = hmac::Key::new(hmac::HMAC_SHA1_FOR_LEGACY_USE_ONLY, key);
30    hmac::sign(&mac, message).as_ref().to_vec()
31}
32
33impl fmt::Display for MessageIntegrity {
34    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
35        write!(f, "KEY: 0x{:x?}", self.0)
36    }
37}
38
39impl Setter for MessageIntegrity {
40    // add_to adds MESSAGE-INTEGRITY attribute to message.
41    //
42    // CPU costly, see BenchmarkMessageIntegrity_AddTo.
43    fn add_to(&self, m: &mut Message) -> Result<()> {
44        for a in &m.attributes.0 {
45            // Message should not contain FINGERPRINT attribute
46            // before MESSAGE-INTEGRITY.
47            if a.typ == ATTR_FINGERPRINT {
48                return Err(Error::ErrFingerprintBeforeIntegrity);
49            }
50        }
51        // The text used as input to HMAC is the STUN message,
52        // including the header, up to and including the attribute preceding the
53        // MESSAGE-INTEGRITY attribute.
54        let length = m.length;
55        // Adjusting m.Length to contain MESSAGE-INTEGRITY TLV.
56        m.length += (MESSAGE_INTEGRITY_SIZE + ATTRIBUTE_HEADER_SIZE) as u32;
57        m.write_length(); // writing length to m.Raw
58        let v = new_hmac(&self.0, &m.raw); // calculating HMAC for adjusted m.Raw
59        m.length = length; // changing m.Length back
60
61        m.add(ATTR_MESSAGE_INTEGRITY, &v);
62
63        Ok(())
64    }
65}
66
67pub(crate) const MESSAGE_INTEGRITY_SIZE: usize = 20;
68
69impl MessageIntegrity {
70    /// New_long_term_integrity returns new MessageIntegrity with key for long-term
71    /// credentials. Password, username, and realm must be SASL-prepared.
72    pub fn new_long_term_integrity(username: String, realm: String, password: String) -> Self {
73        let s = [username, realm, password].join(CREDENTIALS_SEP);
74
75        let mut h = Md5::new();
76        h.update(s.as_bytes());
77
78        MessageIntegrity(h.finalize().as_slice().to_vec())
79    }
80
81    /// New_short_term_integrity returns new MessageIntegrity with key for short-term
82    /// credentials. Password must be SASL-prepared.
83    pub fn new_short_term_integrity(password: String) -> Self {
84        MessageIntegrity(password.as_bytes().to_vec())
85    }
86
87    /// Check checks MESSAGE-INTEGRITY attribute.
88    ///
89    /// CPU costly, see BenchmarkMessageIntegrity_Check.
90    pub fn check(&self, m: &mut Message) -> Result<()> {
91        let v = m.get(ATTR_MESSAGE_INTEGRITY)?;
92
93        // Adjusting length in header to match m.Raw that was
94        // used when computing HMAC.
95
96        let length = m.length as usize;
97        let mut after_integrity = false;
98        let mut size_reduced = 0;
99
100        for a in &m.attributes.0 {
101            if after_integrity {
102                size_reduced += nearest_padded_value_length(a.length as usize);
103                size_reduced += ATTRIBUTE_HEADER_SIZE;
104            }
105            if a.typ == ATTR_MESSAGE_INTEGRITY {
106                after_integrity = true;
107            }
108        }
109        m.length -= size_reduced as u32;
110        m.write_length();
111        // start_of_hmac should be first byte of integrity attribute.
112        let start_of_hmac = MESSAGE_HEADER_SIZE + m.length as usize
113            - (ATTRIBUTE_HEADER_SIZE + MESSAGE_INTEGRITY_SIZE);
114        let b = &m.raw[..start_of_hmac]; // data before integrity attribute
115        let expected = new_hmac(&self.0, b);
116        m.length = length as u32;
117        m.write_length(); // writing length back
118        check_hmac(&v, &expected)
119    }
120}
rtc_stun/integrity.rs

rtc_stun/
integrity.rs
