This implements PR #1051
(https://github.com/tlswg/tls13-spec/pull/1051).

Local experiments were not able to replicate the claims in the PR, but
implement this anyway for comparison purposes.

Change-Id: Ic9baf5e671f9a44565020466a553dd08f5ec0f1b
Reviewed-on: https://boringssl-review.googlesource.com/17844
Reviewed-by: Steven Valdez <svaldez@google.com>
Commit-Queue: Steven Valdez <svaldez@google.com>
CQ-Verified: CQ bot account: commit-bot@chromium.org <commit-bot@chromium.org>

Bug: 132
Change-Id: I2b0c87262a5a529ea264ea8ce2d11c2dba0ec1c8
Reviewed-on: https://boringssl-review.googlesource.com/17766
Reviewed-by: Steven Valdez <svaldez@google.com>
Commit-Queue: David Benjamin <davidben@google.com>

Change-Id: I3de3c48a1de59c2b8de348253ce62a648aa6d6eb
Reviewed-on: https://boringssl-review.googlesource.com/17724
Reviewed-by: David Benjamin <davidben@google.com>
Commit-Queue: David Benjamin <davidben@google.com>
CQ-Verified: CQ bot account: commit-bot@chromium.org <commit-bot@chromium.org>

TLS 1.3 deployment is currently blocked by buggy middleboxes
throughout the ecosystem. As an experiment to better understand these bugs
and the problems they are causing, implement TLS 1.3 variants with
alternate encodings. These are still the same protocol, only encoded
slightly differently. We will use what we learn from these experiments to
guide the TLS 1.3 deployment strategy and proposals to the IETF, if any.

These experiments only target the basic 1-RTT TLS 1.3 handshake. Based on
what we learn from this experiment, we may try future variations to
explore 0-RTT and HelloRetryRequest.

When enabled, the server supports all TLS 1.3 variants while the client
is configured to use a particular variant.

Change-Id: I532411d1abc41314dc76acce0246879b754b4c61
Reviewed-on: https://boringssl-review.googlesource.com/17327
Reviewed-by: David Benjamin <davidben@google.com>
Commit-Queue: David Benjamin <davidben@google.com>
CQ-Verified: CQ bot account: commit-bot@chromium.org <commit-bot@chromium.org>

Like other handshake properties, when in 0-RTT on the client,
SSL_version should report the predicted version. This used to work on
accident because of how ssl->version got set in handshake_client.c early
(and that TLS 1.4 does not exist), but we no longer do that.

Change-Id: Ifb63a22b795fe8964ac553844a46040acd5d7323
Reviewed-on: https://boringssl-review.googlesource.com/17664
Commit-Queue: Steven Valdez <svaldez@google.com>
Reviewed-by: Steven Valdez <svaldez@google.com>
CQ-Verified: CQ bot account: commit-bot@chromium.org <commit-bot@chromium.org>

SSL_set_max_proto_version(TLS1_3_DRAFT_VERSION) worked unintentionally.
Fix that. Also add an error when it fails.

Change-Id: I1048fede7b163e1c170e17bf4370b468221a7077
Reviewed-on: https://boringssl-review.googlesource.com/17525
Reviewed-by: David Benjamin <davidben@google.com>
Commit-Queue: David Benjamin <davidben@google.com>
CQ-Verified: CQ bot account: commit-bot@chromium.org <commit-bot@chromium.org>

This is in preparation for upcoming experiments which will require
supporting multiple experimental versions of TLS 1.3 with, on the
server, the ability to enable multiple variants at once. This means the
version <-> wire bijection no longer exists, even when limiting to a
single SSL*.  Thus version_to_wire is removed and instead we treat the
wire version as the canonical version value.

There is a mapping from valid wire versions to protocol versions which
describe the high-level handshake protocol in use. This mapping is not
injective, so uses of version_from_wire are rewritten differently.

All the version-munging logic is moved to ssl_versions.c with a master
preference list of all TLS and DTLS versions. The legacy version
negotiation is converted to the new scheme. The version lists and
negotiation are driven by the preference lists and a
ssl_supports_version API.

To simplify the mess around SSL_SESSION and versions, version_from_wire
is now DTLS/TLS-agnostic, with any filtering being done by
ssl_supports_version. This is screwy but allows parsing SSL_SESSIONs to
sanity-check it and reject all bogus versions in SSL_SESSION. This
reduces a mess of error cases.

As part of this, the weird logic where ssl->version is set early when
sending the ClientHello is removed. The one place where we were relying
on this behavior is tweaked to query hs->max_version instead.

Change-Id: Ic91b348481ceba94d9ae06d6781187c11adc15b0
Reviewed-on: https://boringssl-review.googlesource.com/17524
Reviewed-by: David Benjamin <davidben@google.com>
Commit-Queue: David Benjamin <davidben@google.com>