deltachat/net/
tls.rs

1//! TLS support.
2use parking_lot::Mutex;
3use std::collections::HashMap;
4use std::sync::Arc;
5
6use anyhow::Result;
7
8use crate::net::session::SessionStream;
9
10use tokio_rustls::rustls;
11use tokio_rustls::rustls::client::ClientSessionStore;
12
13mod danger;
14use danger::NoCertificateVerification;
15
16pub async fn wrap_tls<'a>(
17    strict_tls: bool,
18    hostname: &str,
19    port: u16,
20    use_sni: bool,
21    alpn: &str,
22    stream: impl SessionStream + 'static,
23    tls_session_store: &TlsSessionStore,
24) -> Result<impl SessionStream + 'a> {
25    if strict_tls {
26        let tls_stream =
27            wrap_rustls(hostname, port, use_sni, alpn, stream, tls_session_store).await?;
28        let boxed_stream: Box<dyn SessionStream> = Box::new(tls_stream);
29        Ok(boxed_stream)
30    } else {
31        // We use native_tls because it accepts 1024-bit RSA keys.
32        // Rustls does not support them even if
33        // certificate checks are disabled: <https://github.com/rustls/rustls/issues/234>.
34        let alpns = if alpn.is_empty() {
35            Box::from([])
36        } else {
37            Box::from([alpn])
38        };
39        let tls = async_native_tls::TlsConnector::new()
40            .min_protocol_version(Some(async_native_tls::Protocol::Tlsv12))
41            .use_sni(use_sni)
42            .request_alpns(&alpns)
43            .danger_accept_invalid_hostnames(true)
44            .danger_accept_invalid_certs(true);
45        let tls_stream = tls.connect(hostname, stream).await?;
46        let boxed_stream: Box<dyn SessionStream> = Box::new(tls_stream);
47        Ok(boxed_stream)
48    }
49}
50
51/// Map to store TLS session tickets.
52///
53/// Tickets are separated by port and ALPN
54/// to avoid trying to use Postfix ticket for Dovecot and vice versa.
55/// Doing so would not be a security issue,
56/// but wastes the ticket and the opportunity to resume TLS session unnecessarily.
57/// Rustls takes care of separating tickets that belong to different domain names.
58#[derive(Debug)]
59pub(crate) struct TlsSessionStore {
60    sessions: Mutex<HashMap<(u16, String), Arc<dyn ClientSessionStore>>>,
61}
62
63// This is the default for TLS session store
64// as of Rustls version 0.23.16,
65// but we want to create multiple caches
66// to separate them by port and ALPN.
67const TLS_CACHE_SIZE: usize = 256;
68
69impl TlsSessionStore {
70    /// Creates a new TLS session store.
71    ///
72    /// One such store should be created per profile
73    /// to keep TLS sessions independent.
74    pub fn new() -> Self {
75        Self {
76            sessions: Default::default(),
77        }
78    }
79
80    /// Returns session store for given port and ALPN.
81    ///
82    /// Rustls additionally separates sessions by hostname.
83    pub fn get(&self, port: u16, alpn: &str) -> Arc<dyn ClientSessionStore> {
84        Arc::clone(
85            self.sessions
86                .lock()
87                .entry((port, alpn.to_string()))
88                .or_insert_with(|| {
89                    Arc::new(rustls::client::ClientSessionMemoryCache::new(
90                        TLS_CACHE_SIZE,
91                    ))
92                }),
93        )
94    }
95}
96
97pub async fn wrap_rustls<'a>(
98    hostname: &str,
99    port: u16,
100    use_sni: bool,
101    alpn: &str,
102    stream: impl SessionStream + 'a,
103    tls_session_store: &TlsSessionStore,
104) -> Result<impl SessionStream + 'a> {
105    let mut root_cert_store = rustls::RootCertStore::empty();
106    root_cert_store.extend(webpki_roots::TLS_SERVER_ROOTS.iter().cloned());
107
108    let mut config = rustls::ClientConfig::builder()
109        .with_root_certificates(root_cert_store)
110        .with_no_client_auth();
111    config.alpn_protocols = if alpn.is_empty() {
112        vec![]
113    } else {
114        vec![alpn.as_bytes().to_vec()]
115    };
116
117    // Enable TLS 1.3 session resumption
118    // as defined in <https://www.rfc-editor.org/rfc/rfc8446#section-2.2>.
119    //
120    // Obsolete TLS 1.2 mechanisms defined in RFC 5246
121    // and RFC 5077 have worse security
122    // and are not worth increasing
123    // attack surface: <https://words.filippo.io/we-need-to-talk-about-session-tickets/>.
124    let resumption_store = tls_session_store.get(port, alpn);
125    let resumption = rustls::client::Resumption::store(resumption_store)
126        .tls12_resumption(rustls::client::Tls12Resumption::Disabled);
127    config.resumption = resumption;
128    config.enable_sni = use_sni;
129
130    // Do not verify certificates for hostnames starting with `_`.
131    // They are used for servers with self-signed certificates, e.g. for local testing.
132    // Hostnames starting with `_` can have only self-signed TLS certificates or wildcard certificates.
133    // It is not possible to get valid non-wildcard TLS certificates because CA/Browser Forum requirements
134    // explicitly state that domains should start with a letter, digit or hyphen:
135    // https://github.com/cabforum/servercert/blob/24f38fd4765e019db8bb1a8c56bf63c7115ce0b0/docs/BR.md
136    if hostname.starts_with("_") {
137        config
138            .dangerous()
139            .set_certificate_verifier(Arc::new(NoCertificateVerification::new()));
140    }
141
142    let tls = tokio_rustls::TlsConnector::from(Arc::new(config));
143    let name = tokio_rustls::rustls::pki_types::ServerName::try_from(hostname)?.to_owned();
144    let tls_stream = tls.connect(name, stream).await?;
145    Ok(tls_stream)
146}
deltachat/net/tls.rs

deltachat/net/
tls.rs
