Actually, a TLS/SSLv3 ClientHello message begins with the byte sequence:
offset value
0x00 0x16 content type Handshake
0x01 0x03 major version
0x02 0x00-0x03 minor version
0x03 0x???? length
0x05 0x01 handshake type ClientHello
RFC5246, Appendix A.
Kyle Hamilton wrote:
A client has a sign that a server wants to negotiate TLS if it
receives a byte 0x00 (the code for 'HelloRequest'). A server has a
sign that a client wants to negotiate TLS if it receives a byte 0x01
(ClientHello).
There are multiple ways to use TLS. The one that webservers use is to
create the TLS-encrypted tunnel across TCP, then exchange all
application data over it.
The one that IMAP, ESMTP, and various other state-keeping, text-based
protocols with the ability to send binary across the same connection
use is to create a specific text-based command -- typically STARTTLS
-- that causes the server to send out a HelloRequest.
The typical sequences that I've been looking at for my apps lately, by
the way, are:
Receive: (unicode byte order mark, describing precisely which
encoding the client's using)
STARTTLS
(server sends HelloRequest)
(client sends ClientHello)
Receive: ClientHello
(negotiate TLS)
Receive: Unicode BOM
(server assumes client is using Unicode)
Receive: Telnet IAC (0xff)
(server negotiates telnet parameters, including possibly Unicode)
Receive: anything else
(server assumes client is using ISO-Latin-1)
However, this is primarily for a couple of text-based MUD softwares
that I'm working with. Your mileage may vary.
-Kyle H
On Mon, Jul 6, 2009 at 11:51 AM, Konstantin
Ivanov<[email protected]> wrote:
Hi all,
I was wondering if it is possible to determine if client is requesting an
ssl handshake on regular socket connection and if client does request it,
continue with SSL handshake and enable secure communication? What is
happening is that if I have a server, but I accept a connection using a
regular socket (not OpenSSL accept) then I get the scrambled data from the
client which I assume is an attempt to handshake with the server. Is it
possible to determine if this is a handshake and if so, let this connection
be secure? This is a custom application.
Thank you,
K
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