Version 5.0 The LEDA User Manual

10.7 Secure Socket Streambuffer ( secure
socket streambuf )
1. Definition
An instance sb of class secure socket streambuf can be used as an adapter: It turns a
leda socket s into a C++-streambuf object. This object can be used in standard C++
ostreams and istreams, which makes the communication through the socket easier. Moreover,
secure socket streambuf uses cryptography to secure the communication. Every piece
of data is authenticated, (possibly) compressed and encrypted before it is sent.
If two parties want to use the class secure socket streambuf to exchange data they have
to do the following. First they establish a connection through leda sockets. Then each
party contructs an instance of the class secure socket streambuf which is attached to its
socket. (An example showing how to this can be found at the end of Section 4.14; simply
replace “socket streambuf ” by “secure socket streambuf ” and add the passphrase(s).)
The communication between two instances of the class secure socket streambuf can be
divided in two phases. In the first phase the two parties negotiate session parameters like
packet sizes and they also agree on a so-called session-seed which will be explained later.
In the second phase the actual user data is exchanged. Each phases is protected with
cryptography. The authentication and encryption keys for the first phase are generated
in a deterministic way from the user-supplied passphrase(s). They are called master keys
because they remain the same as long as the passphrases are not changed. In order to
protect the master keys we use them only during the first phase, which consists of two
messages from each party. After that we use the random session seed (in addition to the
passphrases) to compute session keys which are used during the second phase.
#include < LEDA/coding/secure socket streambuf.h >
2. Creation
secure socket streambuf sb(leda socket& s, const CryptByteString& auth passphrase,
const CryptByteString& cipher passphrase,
uint32 out buf sz = DefaultBufferSize,
uint32 in buf sz = DefaultBufferSize,
bool enable compression = false,
bool send acknowledge = false);
creates a sb and attaches it to the socket s. The two passphrases are
used to generate the keys for authentication and encryption. The
parameters out buf sz and in buf sz determine the maximum size of
the out-buffer and the in-buffer. The paramter enable compression
determines whether compression is used. send acknowledge specifies
whether an acknowledgement is sent for every received packet.
Precondition: The connection between the server and the client
must have been established when sb is created.