This patch adds DTLS support to QtNetwork module (and its OpenSSL
back-end).
DTLS over UDP is defined by RFC 6347.
The new API consists of
1) QDtlsClientVerifier which checks if a client that sent us ClientHello
is a real DTLS client by generating a cookie, sending a HelloVerifyRequest
with this cookie attached, and then verifiying a cookie received back.
To be deployed in combination with a server-side QUdpSocket.
2) QDtls - initiates and proceeds with a TLS handshake (client or server
side), with certificates and/or pre-shared key (PSK), and encrypts/decrypts
datagrams after the handshake has finished.
This patch does not implement yet another UDP socket, instead
it allows use of existing QUdpSocket(s), by adding DTLS support
on top. OpenSSL back-end uses a custom BIO to make it work with
QUdpSocket and give a finer control over IO operations.
On the server side, demultiplexing is left to client code (could
be done either by connecting QUdpSocket or by extracting address/port
for an incoming datagram and then forwarding/dispatching them to
the corresponding QDtls object).
Task-number: QTPM-779
Change-Id: Ifcdf8586c70c3018b0c5549efc722e795f2c1c52
Reviewed-by: Edward Welbourne <edward.welbourne@qt.io>
Reviewed-by: Timur Pocheptsov <timur.pocheptsov@qt.io>
Reviewed-by: Mårten Nordheim <marten.nordheim@qt.io>
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