clienthellod: TLS ClientHello/QUIC Initial Packet reflection service

clienthellod, read as "client-hello-D", is a TLS ClientHello/QUIC Initial Packet reflection service. It can be used to parses TLS ClientHello messages and QUIC Initial Packets into human-readable and highly programmable formats such as JSON.

Is is a part of the TLS fingerprintability research project which spans tlsfingerprint.io and quic.tlsfingerprint.io. It parses the ClientHello messages sent by TLS clients and QUIC Client Initial Packets sent by QUIC clients and display the parsed information in a human-readable format with high programmability.

See tlsfingerprint.io and quic.tlsfingerprint.io for more details about the project.

Quick Start

clienthellod comes as a Go library, which can be used to parse both TLS and QUIC protocols.

TLS/QUIC Fingerprinter

    tlsFingerprinter := clienthellod.NewTLSFingerprinter()

    quicFingerprinter := clienthellod.NewQUICFingerprinter()

TLS ClientHello

From a net.Conn

    tcpLis, err := net.Listen("tcp", ":443")
    defer tcpLis.Close()

    conn, err := tcpLis.Accept()
	if err != nil {
        panic(err)
	}
    defer conn.Close()

	ch, err := clienthellod.ReadClientHello(conn) // reads ClientHello from the connection
    if err != nil {
        panic(err)
    }

    err := ch.ParseClientHello() // parses ClientHello's fields
    if err != nil {
        panic(err)
    }

    jsonB, err = json.MarshalIndent(ch, "", "  ")
    if err != nil {
        panic(err)
    }

    fmt.Println(string(jsonB))
    fmt.Println("ClientHello ID: " + ch.HexID) // prints ClientHello's original fingerprint ID calculated using observed TLS extension order
    fmt.Println("ClientHello NormID: " + ch.NormHexID) // prints ClientHello's normalized fingerprint ID calculated using sorted TLS extension list

From raw []byte

    ch, err := clienthellod.UnmarshalClientHello(raw)
    if err != nil {
        panic(err)
    }
    
    // err := ch.ParseClientHello() // no need to call again, UnmarshalClientHello automatically calls ParseClientHello

QUIC Initial Packets (Client-sourced)

Single packet

    udpConn, err := net.ListenUDP("udp", ":443")
    defer udpConn.Close()

    buf := make([]byte, 65535)
    n, addr, err := udpConn.ReadFromUDP(buf)
    if err != nil {
        panic(err)
    }

    ci, err := clienthellod.UnmarshalQUICClientInitialPacket(buf[:n]) // decodes QUIC Client Initial Packet
    if err != nil {
        panic(err)    
    }

    jsonB, err = json.MarshalIndent(cip, "", "  ")
    if err != nil {
        panic(err)
    }

    fmt.Println(string(jsonB)) // including fingerprint IDs of: ClientInitialPacket, QUIC Header, QUIC ClientHello, QUIC Transport Parameters' combination

Multiple packets

Implementations including Chrome/Chromium sends oversized Client Hello which does not fit into one single QUIC packet, in which case multiple QUIC Initial Packets are sent.

    gci := GatherClientInitials() // Each GatherClientInitials reassembles one QUIC Client Initial Packets stream. Use a QUIC Fingerprinter for multiple potential senders, which automatically demultiplexes the packets based on the source address.
    
    udpConn, err := net.ListenUDP("udp", ":443")
    defer udpConn.Close()

    for {
        buf := make([]byte, 65535)
        n, addr, err := udpConn.ReadFromUDP(buf)
        if err != nil {
            panic(err)
        }

        if addr != knownSenderAddr {
            continue
        }

        ci, err := clienthellod.UnmarshalQUICClientInitialPacket(buf[:n]) // decodes QUIC Client Initial Packet
        if err != nil {
            panic(err)    
        }

        err = gci.AddPacket(ci)
        if err != nil {
            panic(err)
        }
    }

Use with Caddy

We also provide clienthellod as a Caddy Module in modcaddy, which you can use with Caddy to capture ClientHello messages and QUIC Client Initial Packets. See modcaddy for more details.

License

This project is developed and distributed under Apache-2.0 license.