Random Extension Order

[Fussballexperte]

When setting Chrome as a predefined browser, I get a random extension order in the JA3 (as expected).

session.Browser = azuretls.Chrome

However, when I set a specific JA3 with session.ApplyJa3(), only this specific JA3 is used every time. There should be an option to explicitly enable extension shuffling in this case, to create a realistic fingerprint from a JA3.

It's possible to use a workaround, but this seems rather ugly:

func enableRandomExtensionOrder(s *azuretls.Session) {
	orig := s.GetClientHelloSpec
	if orig == nil {
		return
	}

	s.GetClientHelloSpec = func() *tls.ClientHelloSpec {
		spec := orig()
		if spec == nil {
			return nil
		}
		spec2 := *spec

		spec2.Extensions = tls.ShuffleChromeTLSExtensions(spec.Extensions)
		return &spec2
	}
}

[Noooste]

Hello,
The lib does not provide extension shuffling with JA3 string.
If you need custom chrome fingerprint with shuffled extension, you will have to implement your own *tls.ClientHelloSpec.

Here is the the default one (azuretls.GetLastChromeVersion) in in the lib for chrome, you can use it as a base for your custom fingerprint.

func GetLastChromeVersion() *tls.ClientHelloSpec {
	return &tls.ClientHelloSpec{
		CipherSuites: []uint16{
			tls.GREASE_PLACEHOLDER,
			tls.TLS_AES_128_GCM_SHA256,
			tls.TLS_AES_256_GCM_SHA384,
			tls.TLS_CHACHA20_POLY1305_SHA256,
			tls.TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256,
			tls.TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256,
			tls.TLS_ECDHE_ECDSA_WITH_AES_256_GCM_SHA384,
			tls.TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384,
			tls.TLS_ECDHE_ECDSA_WITH_CHACHA20_POLY1305_SHA256,
			tls.TLS_ECDHE_RSA_WITH_CHACHA20_POLY1305_SHA256,
			tls.TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA,
			tls.TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA,
			tls.TLS_RSA_WITH_AES_128_GCM_SHA256,
			tls.TLS_RSA_WITH_AES_256_GCM_SHA384,
			tls.TLS_RSA_WITH_AES_128_CBC_SHA,
			tls.TLS_RSA_WITH_AES_256_CBC_SHA,
		},
		CompressionMethods: []byte{
			0x00, // compressionNone
		},
		Extensions: tls.ShuffleChromeTLSExtensions([]tls.TLSExtension{
			&tls.UtlsGREASEExtension{},
			&tls.KeyShareExtension{
				KeyShares: []tls.KeyShare{
					{Group: tls.CurveID(tls.GREASE_PLACEHOLDER), Data: []byte{0}},
					{Group: tls.X25519MLKEM768},
					{Group: tls.X25519},
				},
			},
			&tls.ALPNExtension{AlpnProtocols: []string{
				http2.NextProtoTLS,
				"http/1.1",
			}},
			&tls.SNIExtension{},
			&tls.SignatureAlgorithmsExtension{SupportedSignatureAlgorithms: []tls.SignatureScheme{
				tls.ECDSAWithP256AndSHA256,
				tls.PSSWithSHA256,
				tls.PKCS1WithSHA256,
				tls.ECDSAWithP384AndSHA384,
				tls.PSSWithSHA384,
				tls.PKCS1WithSHA384,
				tls.PSSWithSHA512,
				tls.PKCS1WithSHA512,
			}},
			&tls.ExtendedMasterSecretExtension{},
			&tls.SessionTicketExtension{},
			&tls.SCTExtension{},
			&tls.RenegotiationInfoExtension{},
			&tls.PSKKeyExchangeModesExtension{Modes: []uint8{
				tls.PskModeDHE,
			}},
			&tls.ApplicationSettingsExtensionNew{SupportedProtocols: []string{http2.NextProtoTLS}},
			&tls.UtlsCompressCertExtension{Algorithms: []tls.CertCompressionAlgo{
				tls.CertCompressionBrotli,
			}},
			&tls.SupportedVersionsExtension{Versions: []uint16{
				tls.GREASE_PLACEHOLDER,
				tls.VersionTLS13,
				tls.VersionTLS12,
			}},
			&tls.SupportedCurvesExtension{Curves: []tls.CurveID{
				tls.GREASE_PLACEHOLDER,
				tls.X25519MLKEM768,
				tls.X25519,
				tls.CurveP256,
				tls.CurveP384,
			}},
			&tls.StatusRequestExtension{},
			&tls.SupportedPointsExtension{SupportedPoints: []byte{
				0x00, // pointFormatUncompressed
			}},
			&tls.GREASEEncryptedClientHelloExtension{
				CandidateCipherSuites: []tls.HPKESymmetricCipherSuite{
					{
						KdfId:  dicttls.HKDF_SHA256,
						AeadId: dicttls.AEAD_AES_128_GCM,
					},
				},
				CandidatePayloadLens: []uint16{128, 160, 192, 224}, // +16: 144, 176, 208, 240
			},
			&tls.UtlsGREASEExtension{},
			&tls.UtlsPaddingExtension{GetPaddingLen: tls.BoringPaddingStyle},
		}),
	}
}