Cryptography Reference
In-Depth Information
793 describes exactly how this works and how both sides agree on a source and
destination port and how they sequence these and subsequent packets.
client
server
SYN
SYN/ACK
ACK
Figure 1-1:
TCP three-way handshake
TCP and IP are usually implemented together and called
TCP/IP
. A
socket
refers
to an established TCP connection; both sides, client and server, have a socket
after the
three-way handshake
described above has been completed. If either side
transmits data over this socket, TCP guarantees, to the best of its ability, that the
other side sees this data in the order it was sent. As is required by IP, however,
any intermediate router along the way also sees this data.
SSL
stands for
Secure Sockets Layer
and was originally developed by Netscape
as a way to allow the then-new browser technology to be used for e-commerce.
The original specifi cation proposal can be found in
http://www.mozilla.org/
projects/security/pki/nss/ssl/draft02.html
. Although it has since been
standardized and renamed
Transport Layer Security
(
TLS
), the name SSL is much
more recognizable and in some ways describes better what it does and what
it's for. After a socket has been established between the client and the server,
SSL defi nes a second handshake that can be performed to establish a secure
channel over the inherently insecure TCP layer.
“Insecure” Communications: Understanding the
HTTP Protocol
HTTP
, or
Hypertext Transport Protocol
, which is offi cially described in RFC 2616,
is the standard protocol for web communication. Web clients, typically referred
to as
browsers
, establish sockets with web servers. HTTP has a well-known
destination port of 80. After the socket has been established, the web browser
begins following the rules set forth by the HTTP protocol to request documents.
HTTP started out as a fairly simple protocol in which the client issued a
GET
command and a description of what it would like to get, to which the server
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