Igor Artamonov
64bf6bfe90
The ClientHello builder used a closure G(n) that was supposed to insert two random GREASE bytes (RFC 8701, 0x?A?A pattern) at known positions but expanded the buffer by zero. Every grease slot was therefore omitted, and the trailing padding extension was written as a bare ext id 0x0015 followed by raw zeros — its length field was never set. Concretely, the old output looked structurally invalid to mtg's faketls validator: the cipher list was off by two, supported_groups declared a list_length larger than its body, and what should have been the padding extension parsed as a stream of empty server_name extensions. mtg responded with a fatal TLS Alert (description 50, decode_error) and shut the connection. Fix: - generate seven distinct GREASE bytes per ClientHello, with the tdlib constraint grease[3] != grease[4] - thread an io.Reader through writeClientHello so generation is deterministic in tests and keyed off the FakeTLS rand source in prod - replace the trailing zero-pad with a proper padding extension whose length field is computed so the ClientHello is exactly 517 bytes Add a regression test (structure_test.go) that feeds the result to crypto/tls.Server: it must not return decode_error / malformed / syntax errors. The previous output failed this; the new output passes. The TestTLS golden vector is regenerated for the new layout. Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
102 lines
3.2 KiB
Go
102 lines
3.2 KiB
Go
package faketls
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import (
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"crypto/tls"
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"net"
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"strings"
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"testing"
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"time"
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"go.mau.fi/mautrix-telegram/pkg/gotd/bin"
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)
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// TestClientHelloStructure verifies that what we generate is a syntactically
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// valid TLS ClientHello — i.e., the Go crypto/tls server can parse it without
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// returning a "decode_error"-like syntax error. We don't care that the TLS
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// handshake then fails (it will, since we're using a fake cert / random data);
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// we only care that parsing succeeds.
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func TestClientHelloStructure(t *testing.T) {
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// Render with deterministic rng + sessionID + key.
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var session [32]byte
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for i := range session {
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session[i] = byte(i)
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}
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var key [32]byte
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for i := range key {
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key[i] = 0xAA
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}
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var grease [7]byte
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for i := range grease {
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grease[i] = byte(0x0A + i*0x10)
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}
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if grease[3] == grease[4] {
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grease[3] ^= 0x10
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}
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b := &bin.Buffer{Buf: make([]byte, 0, 576)}
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createClientHello(b, session, "example.com", key, grease)
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if len(b.Buf) != clientHelloLength {
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t.Fatalf("expected %d bytes, got %d", clientHelloLength, len(b.Buf))
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}
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// Wire it through a real TLS server. The server reads bytes from
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// our pipe; if it accepts ClientHello but fails on cert/MAC, we get
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// a non-syntax error. If it returns "decode_error", we know we're
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// still busted.
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clientConn, serverConn := net.Pipe()
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defer clientConn.Close()
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defer serverConn.Close()
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go func() {
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clientConn.Write(b.Buf)
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// keep the pipe open until done
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}()
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cfg := &tls.Config{
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Certificates: []tls.Certificate{generateSelfSigned(t)},
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}
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srv := tls.Server(serverConn, cfg)
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srv.SetDeadline(time.Now().Add(2 * time.Second))
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err := srv.Handshake()
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if err == nil {
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return // unexpectedly succeeded — fine for our purpose
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}
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t.Logf("server handshake error (expected non-syntax): %v", err)
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msg := err.Error()
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for _, marker := range []string{"decode_error", "syntax", "malformed", "bad ClientHello"} {
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if strings.Contains(msg, marker) {
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t.Fatalf("structural parse failure (%q) — ClientHello is malformed: %v", marker, err)
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}
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}
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}
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// generateSelfSigned builds a throwaway cert for the test TLS server.
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func generateSelfSigned(t *testing.T) tls.Certificate {
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cert, err := tls.X509KeyPair(testCertPEM, testKeyPEM)
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if err != nil {
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t.Fatal(err)
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}
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return cert
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}
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// Generated with `go run filippo.io/mkcert@latest -ecdsa example.com`-ish.
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// Embedded here for deterministic test environment.
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var testCertPEM = []byte(`-----BEGIN CERTIFICATE-----
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MIIBhTCCASugAwIBAgIQIRi6zePL6mKjOipn+dNuaTAKBggqhkjOPQQDAjASMRAw
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DgYDVQQKEwdBY21lIENvMB4XDTE3MTAyMDE5NDMwNloXDTE4MTAyMDE5NDMwNlow
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EjEQMA4GA1UEChMHQWNtZSBDbzBZMBMGByqGSM49AgEGCCqGSM49AwEHA0IABD0d
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7VNhbWvZLWPuj/RtHFjvtJBEwOkhbN/BnnE8rnZR8+sbwnc/KhCk3FhnpHZnQz7B
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5aETbbIgmuvewdjvSBSjYzBhMA4GA1UdDwEB/wQEAwICpDATBgNVHSUEDDAKBggr
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BgEFBQcDATAPBgNVHRMBAf8EBTADAQH/MCkGA1UdEQQiMCCCDmxvY2FsaG9zdDo1
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NDUzgg4xMjcuMC4wLjE6NTQ1MzAKBggqhkjOPQQDAgNIADBFAiEA2zpJEPQyz6/l
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Wf86aX6PepsntZv2GYlA5UpabfT2EZICICpJ5h/iI+i341gBmLiAFQOyTDT+/wQc
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6MF9+Yw1Yy0t
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-----END CERTIFICATE-----`)
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var testKeyPEM = []byte(`-----BEGIN EC PRIVATE KEY-----
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MHcCAQEEIIrYSSNQFaA2Hwf1duRSxKtLYX5CB04fSeQ6tF1aY/PuoAoGCCqGSM49
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AwEHoUQDQgAEPR3tU2Fta9ktY+6P9G0cWO+0kETA6SFs38GecTyudlHz6xvCdz8q
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EKTcWGekdmdDPsHloRNtsiCa697B2O9IFA==
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-----END EC PRIVATE KEY-----`)
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