TLS 1.2/1.3 Correctness + Full ServerHello + Rustfmt

Co-Authored-By: brekotis <93345790+brekotis@users.noreply.github.com>

src/cli.rs

@@ -689,6 +689,7 @@ tls_domain = "{domain}"
 mask = true
 mask_port = 443
 fake_cert_len = 2048
+serverhello_compact = false
 tls_full_cert_ttl_secs = 90
 
 [access]

src/config/defaults.rs

@@ -575,6 +575,10 @@ pub(crate) fn default_tls_new_session_tickets() -> u8 {
     0
 }
 
+pub(crate) fn default_serverhello_compact() -> bool {
+    false
+}
+
 pub(crate) fn default_tls_full_cert_ttl_secs() -> u64 {
     90
 }

src/config/hot_reload.rs

@@ -624,6 +624,7 @@ fn warn_non_hot_changes(old: &ProxyConfig, new: &ProxyConfig, non_hot_changed: b
         || old.censorship.server_hello_delay_min_ms != new.censorship.server_hello_delay_min_ms
         || old.censorship.server_hello_delay_max_ms != new.censorship.server_hello_delay_max_ms
         || old.censorship.tls_new_session_tickets != new.censorship.tls_new_session_tickets
+        || old.censorship.serverhello_compact != new.censorship.serverhello_compact
         || old.censorship.tls_full_cert_ttl_secs != new.censorship.tls_full_cert_ttl_secs
         || old.censorship.alpn_enforce != new.censorship.alpn_enforce
         || old.censorship.mask_proxy_protocol != new.censorship.mask_proxy_protocol

src/config/types.rs

@@ -1723,9 +1723,16 @@ pub struct AntiCensorshipConfig {
     #[serde(default = "default_tls_new_session_tickets")]
     pub tls_new_session_tickets: u8,
 
+    /// Enable compact ServerHello payload mode.
+    /// When false, FakeTLS always uses full ServerHello payload behavior.
+    /// When true, compact certificate payload mode can be used by TTL policy.
+    #[serde(default = "default_serverhello_compact")]
+    pub serverhello_compact: bool,
+
     /// TTL in seconds for sending full certificate payload per client IP.
     /// First client connection per (SNI domain, client IP) gets full cert payload.
     /// Subsequent handshakes within TTL use compact cert metadata payload.
+    /// Applied only when `serverhello_compact` is enabled.
     #[serde(default = "default_tls_full_cert_ttl_secs")]
     pub tls_full_cert_ttl_secs: u64,
 
@@ -1820,6 +1827,7 @@ impl Default for AntiCensorshipConfig {
             server_hello_delay_min_ms: default_server_hello_delay_min_ms(),
             server_hello_delay_max_ms: default_server_hello_delay_max_ms(),
             tls_new_session_tickets: default_tls_new_session_tickets(),
+            serverhello_compact: default_serverhello_compact(),
             tls_full_cert_ttl_secs: default_tls_full_cert_ttl_secs(),
             alpn_enforce: default_alpn_enforce(),
             mask_proxy_protocol: 0,

src/maestro/helpers.rs

@@ -549,9 +549,7 @@ pub(crate) fn expected_handshake_close_description(
             std::io::ErrorKind::BrokenPipe => {
                 Some("Peer closed write side before MTProto handshake completed")
             }
-            std::io::ErrorKind::NotConnected => {
-                Some("Handshake socket was already closed by peer")
-            }
+            std::io::ErrorKind::NotConnected => Some("Handshake socket was already closed by peer"),
             _ => None,
         }
     }

src/maestro/listeners.rs

@@ -535,9 +535,8 @@ pub(crate) fn spawn_tcp_accept_loops(
                                         }
                                     }
                                     _ if is_expected_handshake_eof(&e) => {
-                                        let reason = handshake_close_reason.unwrap_or(
-                                            "Peer closed during initial handshake",
-                                        );
+                                        let reason = handshake_close_reason
+                                            .unwrap_or("Peer closed during initial handshake");
                                         if let Some(real_peer) = real_peer {
                                             info!(
                                                 peer = %peer_addr,

src/protocol/tests/tls_security_tests.rs

@@ -1383,6 +1383,8 @@ fn emulated_server_hello_never_places_alpn_in_server_hello_extensions() {
         &session_id,
         &cached,
         false,
+        true,
+        ClientHelloTlsVersion::Tls13,
         &rng,
         Some(b"h2".to_vec()),
         0,
@@ -1624,6 +1626,34 @@ fn test_extract_alpn_multiple() {
     assert_eq!(alpn_str, vec!["h2", "spdy", "h3"]);
 }
 
+#[test]
+fn detect_client_hello_tls_version_prefers_supported_versions_tls13() {
+    let supported_versions = vec![4, 0x03, 0x04, 0x03, 0x03];
+    let ch = build_client_hello_with_exts(vec![(0x002b, supported_versions)], "example.com");
+    assert_eq!(
+        detect_client_hello_tls_version(&ch),
+        Some(ClientHelloTlsVersion::Tls13)
+    );
+}
+
+#[test]
+fn detect_client_hello_tls_version_falls_back_to_legacy_tls12() {
+    let ch = build_client_hello_with_exts(Vec::new(), "example.com");
+    assert_eq!(
+        detect_client_hello_tls_version(&ch),
+        Some(ClientHelloTlsVersion::Tls12)
+    );
+}
+
+#[test]
+fn detect_client_hello_tls_version_rejects_malformed_supported_versions() {
+    // list_len=3 is invalid because version vector must contain u16 pairs.
+    let malformed_supported_versions = vec![3, 0x03, 0x04, 0x03];
+    let ch =
+        build_client_hello_with_exts(vec![(0x002b, malformed_supported_versions)], "example.com");
+    assert!(detect_client_hello_tls_version(&ch).is_none());
+}
+
 #[test]
 fn extract_sni_rejects_zero_length_host_name() {
     let mut sni_ext = Vec::new();

src/protocol/tls.rs

@@ -811,6 +811,128 @@ pub fn extract_alpn_from_client_hello(handshake: &[u8]) -> Vec<Vec<u8>> {
     out
 }
 
+/// ClientHello TLS generation inferred from handshake fields.
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum ClientHelloTlsVersion {
+    Tls12,
+    Tls13,
+}
+
+/// Detect TLS generation from a ClientHello.
+///
+/// The parser prefers `supported_versions` (0x002b) when present and falls back
+/// to `legacy_version` for compatibility with TLS 1.2 style hellos.
+pub fn detect_client_hello_tls_version(handshake: &[u8]) -> Option<ClientHelloTlsVersion> {
+    if handshake.len() < 5 || handshake[0] != TLS_RECORD_HANDSHAKE {
+        return None;
+    }
+
+    let record_len = u16::from_be_bytes([handshake[3], handshake[4]]) as usize;
+    if handshake.len() < 5 + record_len {
+        return None;
+    }
+
+    let mut pos = 5; // after record header
+    if handshake.get(pos) != Some(&0x01) {
+        return None; // not ClientHello
+    }
+    pos += 1; // message type
+
+    if pos + 3 > handshake.len() {
+        return None;
+    }
+    let handshake_len = ((handshake[pos] as usize) << 16)
+        | ((handshake[pos + 1] as usize) << 8)
+        | handshake[pos + 2] as usize;
+    pos += 3; // handshake length bytes
+    if pos + handshake_len > 5 + record_len {
+        return None;
+    }
+
+    if pos + 2 + 32 > handshake.len() {
+        return None;
+    }
+    let legacy_version = u16::from_be_bytes([handshake[pos], handshake[pos + 1]]);
+    pos += 2 + 32; // version + random
+
+    let session_id_len = *handshake.get(pos)? as usize;
+    pos += 1 + session_id_len;
+    if pos + 2 > handshake.len() {
+        return None;
+    }
+
+    let cipher_len = u16::from_be_bytes([handshake[pos], handshake[pos + 1]]) as usize;
+    pos += 2 + cipher_len;
+    if pos >= handshake.len() {
+        return None;
+    }
+
+    let comp_len = *handshake.get(pos)? as usize;
+    pos += 1 + comp_len;
+    if pos + 2 > handshake.len() {
+        return None;
+    }
+
+    let ext_len = u16::from_be_bytes([handshake[pos], handshake[pos + 1]]) as usize;
+    pos += 2;
+    let ext_end = pos + ext_len;
+    if ext_end > handshake.len() {
+        return None;
+    }
+
+    let mut saw_supported_versions = false;
+    while pos + 4 <= ext_end {
+        let etype = u16::from_be_bytes([handshake[pos], handshake[pos + 1]]);
+        let elen = u16::from_be_bytes([handshake[pos + 2], handshake[pos + 3]]) as usize;
+        pos += 4;
+        if pos + elen > ext_end {
+            return None;
+        }
+
+        if etype == extension_type::SUPPORTED_VERSIONS {
+            saw_supported_versions = true;
+            if elen < 1 {
+                return None;
+            }
+            let list_len = handshake[pos] as usize;
+            if list_len == 0 || list_len % 2 != 0 || 1 + list_len > elen {
+                return None;
+            }
+
+            let mut has_tls12 = false;
+            let mut ver_pos = pos + 1;
+            let ver_end = ver_pos + list_len;
+            while ver_pos + 1 < ver_end {
+                let version = u16::from_be_bytes([handshake[ver_pos], handshake[ver_pos + 1]]);
+                if version == 0x0304 {
+                    return Some(ClientHelloTlsVersion::Tls13);
+                }
+                if version == 0x0303 || version == 0x0302 || version == 0x0301 {
+                    has_tls12 = true;
+                }
+                ver_pos += 2;
+            }
+
+            if has_tls12 {
+                return Some(ClientHelloTlsVersion::Tls12);
+            }
+            return None;
+        }
+
+        pos += elen;
+    }
+
+    if saw_supported_versions {
+        return None;
+    }
+
+    if legacy_version >= 0x0303 {
+        Some(ClientHelloTlsVersion::Tls12)
+    } else {
+        None
+    }
+}
+
 /// Check if bytes look like a TLS ClientHello
 pub fn is_tls_handshake(first_bytes: &[u8]) -> bool {
     if first_bytes.len() < 3 {

src/proxy/handshake.rs

@@ -1119,6 +1119,10 @@ where
     } else {
         None
     };
+    // Fail-closed to TLS 1.3 semantics when ClientHello version is ambiguous:
+    // this avoids leaking certificate payload on malformed probes.
+    let client_tls_version = tls::detect_client_hello_tls_version(handshake)
+        .unwrap_or(tls::ClientHelloTlsVersion::Tls13);
 
     if client_sni.is_some() && matched_tls_domain.is_none() && preferred_user_hint.is_none() {
         let sni = client_sni.as_deref().unwrap_or_default();
@@ -1439,12 +1443,18 @@ where
             let selected_domain =
                 matched_tls_domain.unwrap_or(config.censorship.tls_domain.as_str());
             let cached_entry = cache.get(selected_domain).await;
-            let use_full_cert_payload = cache
-                .take_full_cert_budget_for_ip(
-                    peer.ip(),
-                    Duration::from_secs(config.censorship.tls_full_cert_ttl_secs),
-                )
-                .await;
+            let use_full_cert_payload = if config.censorship.serverhello_compact
+                && matches!(client_tls_version, tls::ClientHelloTlsVersion::Tls12)
+            {
+                cache
+                    .take_full_cert_budget_for_ip(
+                        peer.ip(),
+                        Duration::from_secs(config.censorship.tls_full_cert_ttl_secs),
+                    )
+                    .await
+            } else {
+                true
+            };
             Some((cached_entry, use_full_cert_payload))
         } else {
             None
@@ -1465,6 +1475,8 @@ where
             validation_session_id_slice,
             &cached_entry,
             use_full_cert_payload,
+            config.censorship.serverhello_compact,
+            client_tls_version,
             rng,
             selected_alpn.clone(),
             config.censorship.tls_new_session_tickets,

src/tls_front/emulator.rs

@@ -5,7 +5,9 @@ use crate::protocol::constants::{
     MAX_TLS_CIPHERTEXT_SIZE, TLS_RECORD_APPLICATION, TLS_RECORD_CHANGE_CIPHER,
     TLS_RECORD_HANDSHAKE, TLS_VERSION,
 };
-use crate::protocol::tls::{TLS_DIGEST_LEN, TLS_DIGEST_POS, gen_fake_x25519_key};
+use crate::protocol::tls::{
+    ClientHelloTlsVersion, TLS_DIGEST_LEN, TLS_DIGEST_POS, gen_fake_x25519_key,
+};
 use crate::tls_front::types::{CachedTlsData, ParsedCertificateInfo, TlsProfileSource};
 use crc32fast::Hasher;
 
@@ -190,6 +192,8 @@ pub fn build_emulated_server_hello(
     session_id: &[u8],
     cached: &CachedTlsData,
     use_full_cert_payload: bool,
+    serverhello_compact: bool,
+    client_tls_version: ClientHelloTlsVersion,
     rng: &SecureRandom,
     alpn: Option<Vec<u8>>,
     new_session_tickets: u8,
@@ -265,20 +269,33 @@ pub fn build_emulated_server_hello(
             }
         }
     };
-    let compact_payload = cached
-        .cert_info
-        .as_ref()
-        .and_then(build_compact_cert_info_payload)
-        .and_then(hash_compact_cert_info_payload);
-    let selected_payload: Option<&[u8]> = if use_full_cert_payload {
+    let compact_payload = if serverhello_compact {
         cached
-            .cert_payload
+            .cert_info
             .as_ref()
-            .map(|payload| payload.certificate_message.as_slice())
-            .filter(|payload| !payload.is_empty())
-            .or(compact_payload.as_deref())
+            .and_then(build_compact_cert_info_payload)
+            .and_then(hash_compact_cert_info_payload)
     } else {
-        compact_payload.as_deref()
+        None
+    };
+    let full_payload = cached
+        .cert_payload
+        .as_ref()
+        .map(|payload| payload.certificate_message.as_slice())
+        .filter(|payload| !payload.is_empty());
+    let selected_payload: Option<&[u8]> = match client_tls_version {
+        ClientHelloTlsVersion::Tls13 => None,
+        ClientHelloTlsVersion::Tls12 => {
+            if serverhello_compact {
+                if use_full_cert_payload {
+                    full_payload.or(compact_payload.as_deref())
+                } else {
+                    compact_payload.as_deref()
+                }
+            } else {
+                full_payload
+            }
+        }
     };
 
     if let Some(payload) = selected_payload {
@@ -402,6 +419,7 @@ mod tests {
     use crate::protocol::constants::{
         TLS_RECORD_APPLICATION, TLS_RECORD_CHANGE_CIPHER, TLS_RECORD_HANDSHAKE,
     };
+    use crate::protocol::tls::ClientHelloTlsVersion;
 
     fn first_app_data_payload(response: &[u8]) -> &[u8] {
         let hello_len = u16::from_be_bytes([response[3], response[4]]) as usize;
@@ -448,6 +466,8 @@ mod tests {
             &[0x22; 16],
             &cached,
             true,
+            true,
+            ClientHelloTlsVersion::Tls12,
             &rng,
             None,
             0,
@@ -474,6 +494,8 @@ mod tests {
             &[0x33; 16],
             &cached,
             true,
+            true,
+            ClientHelloTlsVersion::Tls12,
             &rng,
             None,
             0,
@@ -506,6 +528,8 @@ mod tests {
             &[0x55; 16],
             &cached,
             false,
+            true,
+            ClientHelloTlsVersion::Tls12,
             &rng,
             None,
             0,
@@ -529,6 +553,68 @@ mod tests {
         );
     }
 
+    #[test]
+    fn test_build_emulated_server_hello_tls13_never_uses_cert_payload() {
+        let cert_msg = vec![0x0b, 0x00, 0x00, 0x05, 0x00, 0xaa, 0xbb, 0xcc, 0xdd];
+        let cached = make_cached(Some(TlsCertPayload {
+            cert_chain_der: vec![vec![0x30, 0x01, 0x00]],
+            certificate_message: cert_msg.clone(),
+        }));
+
+        let rng = SecureRandom::new();
+        let response = build_emulated_server_hello(
+            b"secret",
+            &[0x56; 32],
+            &[0x78; 16],
+            &cached,
+            true,
+            true,
+            ClientHelloTlsVersion::Tls13,
+            &rng,
+            None,
+            0,
+        );
+
+        let payload = first_app_data_payload(&response);
+        assert!(
+            !payload.starts_with(&cert_msg),
+            "TLS 1.3 response path must not expose certificate payload bytes"
+        );
+    }
+
+    #[test]
+    fn test_build_emulated_server_hello_compact_disabled_skips_compact_payload() {
+        let mut cached = make_cached(None);
+        cached.cert_info = Some(crate::tls_front::types::ParsedCertificateInfo {
+            not_after_unix: Some(1_900_000_000),
+            not_before_unix: Some(1_700_000_000),
+            issuer_cn: Some("Issuer".to_string()),
+            subject_cn: Some("example.com".to_string()),
+            san_names: vec!["example.com".to_string()],
+        });
+
+        let rng = SecureRandom::new();
+        let response = build_emulated_server_hello(
+            b"secret",
+            &[0x90; 32],
+            &[0x91; 16],
+            &cached,
+            false,
+            false,
+            ClientHelloTlsVersion::Tls12,
+            &rng,
+            Some(b"h2".to_vec()),
+            0,
+        );
+
+        let payload = first_app_data_payload(&response);
+        let expected_alpn_marker = [0x00u8, 0x10, 0x00, 0x05, 0x00, 0x03, 0x02, b'h', b'2'];
+        assert!(
+            payload.starts_with(&expected_alpn_marker),
+            "when compact mode is disabled and no full cert payload exists, the random/alpn path must be used"
+        );
+    }
+
     #[test]
     fn test_build_emulated_server_hello_ignores_tail_records_for_profiled_tls() {
         let mut cached = make_cached(None);
@@ -545,6 +631,8 @@ mod tests {
             &[0x34; 16],
             &cached,
             false,
+            true,
+            ClientHelloTlsVersion::Tls13,
             &rng,
             None,
             0,

src/tls_front/tests/emulator_profile_fidelity_security_tests.rs

@@ -4,6 +4,7 @@ use crate::crypto::SecureRandom;
 use crate::protocol::constants::{
     TLS_RECORD_APPLICATION, TLS_RECORD_CHANGE_CIPHER, TLS_RECORD_HANDSHAKE,
 };
+use crate::protocol::tls::ClientHelloTlsVersion;
 use crate::tls_front::emulator::build_emulated_server_hello;
 use crate::tls_front::types::{
     CachedTlsData, ParsedServerHello, TlsBehaviorProfile, TlsProfileSource,
@@ -62,6 +63,8 @@ fn emulated_server_hello_keeps_single_change_cipher_spec_for_client_compatibilit
         &[0x72; 16],
         &cached,
         false,
+        true,
+        ClientHelloTlsVersion::Tls13,
         &rng,
         None,
         0,
@@ -84,6 +87,8 @@ fn emulated_server_hello_does_not_emit_profile_ticket_tail_when_disabled() {
         &[0x82; 16],
         &cached,
         false,
+        true,
+        ClientHelloTlsVersion::Tls13,
         &rng,
         None,
         0,
@@ -104,6 +109,8 @@ fn emulated_server_hello_uses_profile_ticket_lengths_when_enabled() {
         &[0x92; 16],
         &cached,
         false,
+        true,
+        ClientHelloTlsVersion::Tls13,
         &rng,
         None,
         2,

src/tls_front/tests/emulator_security_tests.rs

@@ -4,6 +4,7 @@ use crate::crypto::SecureRandom;
 use crate::protocol::constants::{
     TLS_RECORD_APPLICATION, TLS_RECORD_CHANGE_CIPHER, TLS_RECORD_HANDSHAKE,
 };
+use crate::protocol::tls::ClientHelloTlsVersion;
 use crate::tls_front::emulator::build_emulated_server_hello;
 use crate::tls_front::types::{
     CachedTlsData, ParsedServerHello, TlsBehaviorProfile, TlsCertPayload, TlsProfileSource,
@@ -55,6 +56,8 @@ fn emulated_server_hello_ignores_oversized_alpn_when_marker_would_not_fit() {
         &[0x22; 16],
         &cached,
         true,
+        true,
+        ClientHelloTlsVersion::Tls13,
         &rng,
         Some(oversized_alpn),
         0,
@@ -91,6 +94,8 @@ fn emulated_server_hello_embeds_full_alpn_marker_when_body_can_fit() {
         &[0x41; 16],
         &cached,
         true,
+        true,
+        ClientHelloTlsVersion::Tls13,
         &rng,
         Some(b"h2".to_vec()),
         0,
@@ -119,6 +124,8 @@ fn emulated_server_hello_prefers_cert_payload_over_alpn_marker() {
         &[0x42; 16],
         &cached,
         true,
+        true,
+        ClientHelloTlsVersion::Tls12,
         &rng,
         Some(b"h2".to_vec()),
         0,