Class TLSClientHello

scapy/layers/tls/handshake.py:253–349

TLS ClientHello, with abilities to handle extensions. The Random structure follows the RFC 5246: while it is 32-byte long, many implementations use the first 4 bytes as a gmt_unix_time, and then the remaining 28 byts should be completely random. This was designed in order to (s

###############################################################################

class TLSClientHello(_TLSHandshake):
    """
    TLS ClientHello, with abilities to handle extensions.

    The Random structure follows the RFC 5246: while it is 32-byte long,
    many implementations use the first 4 bytes as a gmt_unix_time, and then
    the remaining 28 byts should be completely random. This was designed in
    order to (sort of) mitigate broken RNGs. If you prefer to show the full
    32 random bytes without any GMT time, just comment in/out the lines below.
    """
    name = "TLS Handshake - Client Hello"
    fields_desc = [ByteEnumField("msgtype", 1, _tls_handshake_type),
                   ThreeBytesField("msglen", None),
                   _TLSClientVersionField("version", None, _tls_version),

                   # _TLSRandomBytesField("random_bytes", None, 32),
                   _GMTUnixTimeField("gmt_unix_time", None),
                   _TLSRandomBytesField("random_bytes", None, 28),

                   FieldLenField("sidlen", None, fmt="B", length_of="sid"),
                   _SessionIDField("sid", "",
                                   length_from=lambda pkt: pkt.sidlen),

                   FieldLenField("cipherslen", None, fmt="!H",
                                 length_of="ciphers"),
                   _CipherSuitesField("ciphers", None,
                                      _tls_cipher_suites, itemfmt="!H",
                                      length_from=lambda pkt: pkt.cipherslen),

                   FieldLenField("complen", None, fmt="B", length_of="comp"),
                   _CompressionMethodsField("comp", [0],
                                            _tls_compression_algs,
                                            itemfmt="B",
                                            length_from=lambda pkt: pkt.complen),  # noqa: E501

                   _ExtensionsLenField("extlen", None, length_of="ext"),
                   _ExtensionsField("ext", None,
                                    length_from=lambda pkt: (pkt.msglen -
                                                             (pkt.sidlen or 0) -  # noqa: E501
                                                             (pkt.cipherslen or 0) -  # noqa: E501
                                                             (pkt.complen or 0) -  # noqa: E501
                                                             40))]

    def post_build(self, p, pay):
        if self.random_bytes is None:
            p = p[:10] + randstring(28) + p[10 + 28:]

        # if no ciphersuites were provided, we add a few usual, supported
        # ciphersuites along with the appropriate extensions
        if self.ciphers is None:
            cipherstart = 39 + (self.sidlen or 0)
            s = b"001ac02bc023c02fc027009e0067009c003cc009c0130033002f000a"
            p = p[:cipherstart] + hex_bytes(s) + p[cipherstart + 2:]
            if self.ext is None:
                ext_len = b'\x00\x2c'
                ext_reneg = b'\xff\x01\x00\x01\x00'
                ext_sn = b'\x00\x00\x00\x0f\x00\r\x00\x00\nsecdev.org'
                ext_sigalg = b'\x00\r\x00\x08\x00\x06\x04\x03\x04\x01\x02\x01'