This CL removes the last of the EVP_CIPHER codepath in ssl/. The dead code is
intentionally not pruned for ease of review, except in DTLS-only code where
adding new logic to support both, only to remove half, would be cumbersome.

Fixes made:
- dtls1_retransmit_state is taught to retain aead_write_ctx rather than
  enc_write_ctx.
- d1_pkt.c reserves space for the variable-length nonce when echoed into the
  packet.
- dtls1_do_write sizes the MTU based on EVP_AEAD max overhead.
- tls1_change_cipher_state_cipher should not free AEAD write contexts in DTLS.
  This matches the (rather confused) ownership for the EVP_CIPHER contexts.
  I've added a TODO to resolve this craziness.

A follow-up CL will remove all the resultant dead code.

Change-Id: I644557f4db53bbfb182950823ab96d5e4c908866
Reviewed-on: https://boringssl-review.googlesource.com/2699
Reviewed-by: Adam Langley <agl@google.com>

This avoids needing a should_add_to_finished_hash boolean on do_write. The
logic in do_write was a little awkward because do_write would be called
multiple times if the write took several iterations. This also gets complex if
DTLS retransmits are involved. (At a glance, it's not obvious the
BIO_CTRL_DGRAM_MTU_EXCEEDED case actually works.)

Doing it as the handshake message is being prepared avoids this concern. It
also gives a natural point for the extended master secret logic which needs to
do work after the finished hash has been sampled.

As a bonus, we can remove s->d1->retransmitting which was only used to deal
with this issue.

Change-Id: Ifedf23ee4a6c5e08f960d296a6eb1f337a16dc7a
Reviewed-on: https://boringssl-review.googlesource.com/2604
Reviewed-by: Adam Langley <agl@google.com>

This makes SSLv23_method go through DTLS_ANY_VERSION's version negotiation
logic. This allows us to get rid of duplicate ClientHello logic. For
compatibility, SSL_METHOD is now split into SSL_PROTOCOL_METHOD and a version.
The legacy version-locked methods set min_version and max_version based this
version field to emulate the original semantics.

As a bonus, we can now handle fragmented ClientHello versions now.

Because SSLv23_method is a silly name, deprecate that too and introduce
TLS_method.

Change-Id: I8b3df2b427ae34c44ecf972f466ad64dc3dbb171

Parameters like these should not change between 32-bit and 64-bit. 64 is also
the value recommended in RFC 6347, section 4.1.2.6. Document those fields while
I'm here.

Change-Id: I8481ee0765ff3d261a96a2e1a53b6ad6695b2d42
Reviewed-on: https://boringssl-review.googlesource.com/2222
Reviewed-by: Adam Langley <agl@google.com>

This was added in http://rt.openssl.org/Ticket/Display.html?id=2033 to support
a mode where a DTLS socket would statelessly perform the ClientHello /
HelloVerifyRequest portion of the handshake, to be handed off to a socket
specific to this peer address.

This is not used by WebRTC or other current consumers. If we need to support
something like this, it would be cleaner to do the listen portion (cookieless
ClientHello + HelloVerifyRequest) externally and then spin up an SSL instance
on receipt of a cookied ClientHello. This would require a slightly more complex
BIO to replay the second ClientHello but would avoid peppering the DTLS
handshake state with a special short-circuiting mode.

Change-Id: I7a413932edfb62f8b9368912a9a0621d4155f1aa
Reviewed-on: https://boringssl-review.googlesource.com/2220
Reviewed-by: Adam Langley <agl@google.com>

This code isn't compiled in. It seems there was some half-baked logic for a
7-byte alert that includes more information about handshake messages
retransmit.

No such alert exists, and the code had a FIXME anyway. If it gets resurrected
in DTLS 1.3 or some extension, we can deal with it then.

Change-Id: I8784ea8ee44bb8da4b0fe5d5d507997526557432
Reviewed-on: https://boringssl-review.googlesource.com/2121
Reviewed-by: Adam Langley <agl@google.com>

Rather than switching the order of the ServerHello and HelloVerifyRequest
states and processing each twice, have the states follow the protocol order.
HelloVerifyRequest reading is optional and ServerHello is strict. Use the
send_cookie bit to determine whether we're expecting a cookie or not.

Fix the dtls1_stop_timer call in these states to consistently hit the end of a
server flight; the previous flight should not be cleared from the retransmit
buffer until the entire next flight is received. That said, OpenSSL doesn't
appear to implement the part where, on receipt of the previous peer flight, the
buffered flight is retransmitted. (With the exception of a SSL3_MT_FINISHED
special-case in dtls1_read_bytes.) So if the peer is also OpenSSL, this doesn't
do anything.

Also fix the DTLS test which wasn't actually asserting that the ClientHello
matched.

Change-Id: Ia542190972dbffabb837d32c9d453a243caa90b2
Reviewed-on: https://boringssl-review.googlesource.com/1551
Reviewed-by: Adam Langley <agl@google.com>

I see no internal users and the existence of a THIRD version encoding
complicates all version-checking logic. Also convert another version check to
SSL_IS_DTLS that was missed earlier.

Change-Id: I60d215f57d44880f6e6877889307dc39dbf838f7
Reviewed-on: https://boringssl-review.googlesource.com/1550
Reviewed-by: Adam Langley <agl@google.com>

const-correctness, unsigned long -> size_t.

Change-Id: Ic0c2685a48a0f98396c5753b6077c6c0c3b92326
Reviewed-on: https://boringssl-review.googlesource.com/1540
Reviewed-by: Adam Langley <agl@google.com>

Windows doesn't have ssize_t, sadly. There's SSIZE_T, but defining an
OPENSSL_SSIZE_T seems worse than just using an int.

Change-Id: I09bb5aa03f96da78b619e551f92ed52ce24d9f3f
Reviewed-on: https://boringssl-review.googlesource.com/1352
Reviewed-by: Adam Langley <agl@google.com>

Also fix some DTLS cookie bugs. rcvd_cookie is never referenced after being
saved (and the length isn't saved, so it couldn't be used anyway), and the
cookie verification failed to check the length.

For convenience, add a CBS_mem_equal helper function. Saves a bit of
repetition.

Change-Id: I187137733b069f0ac8d8b1bf151eeb80d388b971
Reviewed-on: https://boringssl-review.googlesource.com/1174
Reviewed-by: Adam Langley <agl@google.com>

Previously, public headers lived next to the respective code and there
were symlinks from include/openssl to them.

This doesn't work on Windows.

This change moves the headers to live in include/openssl. In cases where
some symlinks pointed to the same header, I've added a file that just
includes the intended target. These cases are all for backwards-compat.

Change-Id: I6e285b74caf621c644b5168a4877db226b07fd92
Reviewed-on: https://boringssl-review.googlesource.com/1180
Reviewed-by: David Benjamin <davidben@chromium.org>
Reviewed-by: Adam Langley <agl@google.com>

Initial fork from f2d678e6e8 (1.0.2 beta).

(This change contains substantial changes from the original and
effectively starts a new history.)