As per RFC, if TLS server cannot pickup a suitable cipher from a client
list, it has to send handshake_failure alert. For us it means that we
have to route a request to a fronting domain, because we want to have it
exactly like a real webserver does. So, if it misbehaves, so do we.
This PR adds a new setting to the config: `network.timeout`. This setting
defines a time period during which all handshake procedures and
ceremonies must be completed. If not - connection is aborted. This
should help in situations when connection is established but client
cannot continue for some reason (for example, RST sent by some middle box).
Instead of echoing the first cipher suite from ClientHello (which is
often a GREASE value like 0x5a5a), iterate the list and pick the first
real cipher suite. This is what real TLS servers do per RFC 8701.
Production data shows two client profiles:
- 87% send GREASE first, then 0x1301 (TLS_AES_128_GCM_SHA256)
- 13% send 0xc02b first (TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256)
The fix correctly selects 0x1301 or 0xc02b respectively, matching
real server behavior. Fallback to 0x1301 if all suites are GREASE.
Add snapshot test with GREASE as first cipher suite.
DPI bypass tools like ByeDPI fragment a single TLS record into multiple
records to evade censorship. This broke ReadClientHello because it
assumed the entire ClientHello arrives in one TLS record.
Add reassembleTLSHandshake that reads continuation records and
reconstructs a single TLS record before parsing and HMAC verification.
Per RFC 5246 Section 6.2.1, handshake messages may be fragmented
across multiple records — this is valid TLS behavior.
9seconds
Sergei ArkhipovandGitHub
Constantine
appolimp