Some TLS extensions were disabled for DTLS. Possibly because they caused
problems with the old duplicated code. Enable them again.

Use the enc_flags field to determine whether we should use explicit IV,
signature algorithms or SHA256 default PRF instead of hard coding which
versions support each requirement.

Revise DTLS code. There was a *lot* of code duplication in the
DTLS code that generates records. This makes it harder to maintain and
sometimes a TLS update is omitted by accident from the DTLS code.

Specifically almost all of the record generation functions have code like
this:

some_pointer = buffer + HANDSHAKE_HEADER_LENGTH;
... Record creation stuff ...
set_handshake_header(ssl, SSL_MT_SOMETHING, message_len);

...

write_handshake_message(ssl);

Where the "Record creation stuff" is identical between SSL/TLS and DTLS or
in some cases has very minor differences.

By adding a few fields to SSL3_ENC to include the header length, some flags
and function pointers for handshake header setting and handshake writing the
code can cope with both cases.

Note: although this passes "make test" and some simple DTLS tests there may
be some minor differences in the DTLS code that have to be accounted for.

This change adds CRYPTO_memcmp, which compares two vectors of bytes in
an amount of time that's independent of their contents. It also changes
several MAC compares in the code to use this over the standard memcmp,
which may leak information about the size of a matching prefix.
(cherry picked from commit 2ee798880a246d648ecddadc5b91367bee4a5d98)

side, if possible.

Don't advertise compressed char2 for SuiteB as it is not supported.

new feature: if ctx==NULL in SSL_CTX_ctrl perform syntax checking only for some operations (currently curves and signature algorithms)

change the current certificate (in s->cert->key) to the one used and then
SSL_get_certificate and SSL_get_privatekey will automatically work.

right response is stapled. Also change SSL_get_certificate() so it
returns the certificate actually sent.  See
http://rt.openssl.org/Ticket/Display.html?id=2836.

some invalid operations for testing purposes. Currently this can be used
to sign using digests the peer doesn't support, EC curves the peer
doesn't support and use certificates which don't match the type associated
with a ciphersuite.

by a certificate chain. Add additional tests to handle client
certificates: checks for matching certificate type and issuer name
comparison.

Print out results of checks for each candidate chain tested in
s_server/s_client.

that are disabled for this session (as opposed to always disabled by
configuration).

the permitted signature algorithms for server and client authentication
are the same but it is now possible to set different algorithms for client
authentication only.

is required by client or server. An application can decide which
certificate chain to present based on arbitrary criteria: for example
supported signature algorithms. Add very simple example to s_server.
This fixes many of the problems and restrictions of the existing client
certificate callback: for example you can now clear existing certificates
and specify the whole chain.

appropriate checks in tls1_check_chain.

the certificate can be used for (if anything). Set valid_flags field
in new tls1_check_chain function. Simplify ssl_set_cert_masks which used
to have similar checks in it.

Add new "cert_flags" field to CERT structure and include a "strict mode".
This enforces some TLS certificate requirements (such as only permitting
certificate signature algorithms contained in the supported algorithms
extension) which some implementations ignore: this option should be used
with caution as it could cause interoperability issues.

Only store encoded versions of peer and configured signature algorithms.
Determine shared signature algorithms and cache the result along with NID
equivalents of each algorithm.

TLS v1.2. These are sent as an extension for clients and during a certificate
request for servers.

TODO: add support for shared signature algorithms, respect shared algorithms
when deciding which ciphersuites and certificates to permit.

Reviewed by: steve
Improved localisation of TLS extension handling and code tidy.

Localize client hello extension parsing in t1_lib.c