peer_sigalgs should live on SSL_HANDSHAKE. This both releases a little
bit of memory after the handshake is over and also avoids the bug where
the sigalgs get dropped if SSL_set_SSL_CTX is called at a bad time. See
also upstream's 14e14bf696.

This only affects consumers using the old SNI callback and not
select_certificate_cb.

Add a test that the SNI callback works as expected. In doing so, add an
SSL_CTX version of the signing preferences API. This is a property of
the cert/key pair (really just the key) and should be tied to that. This
makes it a bit easier to have the regression test work with TLS 1.2 too.

I thought we'd fixed this already, but apparently not... :-/

BUG=95

Change-Id: I75b02fad4059e6aa46c3b05183a07d72880711b3
Reviewed-on: https://boringssl-review.googlesource.com/10445
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>

Having two copies of this is confusing. This field is inherently tied to
the certificate chain, which lives on SSL_SESSION, so this should live
there too. This also wasn't getting reset correctly on SSL_clear, but
this is now resolved.

Change-Id: I22b1734a93320bb0bf0dc31faa74d77a8e1de906
Reviewed-on: https://boringssl-review.googlesource.com/10283
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>

Per Piotr, all caps is the proper rendering.

Change-Id: I783016a6ed7e29f49369fabbcfa49b66910e4954
Reviewed-on: https://boringssl-review.googlesource.com/10486
Reviewed-by: Piotr Sikora <piotrsikora@google.com>
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>

9498e74 changed the default value of verify_result to an error. This
tripped up NGINX, which depends on a bug[1] in OpenSSL. netty-tcnative
also uses this behavior, though it currently isn't tripped up by 9498e74
because it calls |SSL_set_verify_result|. However, we would like to
remove |SSL_set_verify_result| and with two data points, it seems this
is behavior we must preserve.

This change sets |verify_result| to |X509_V_OK| when a) no client
certificate is requested or b) none is given and it's optional.

[1] See BUGS in https://www.openssl.org/docs/manmaster/ssl/SSL_get_verify_result.html

Change-Id: Ibd33660ae409bfe272963a8c39b7e9aa83c3d635
Reviewed-on: https://boringssl-review.googlesource.com/9067
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>

BUG=75

Change-Id: Ied864cfccbc0e68d71c55c5ab563da27b7253463
Reviewed-on: https://boringssl-review.googlesource.com/9043
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>

Since we are eliminating DHE support in TLS, this is just a waste of
bytes.

Change-Id: I3a23ece564e43f7e8874d1ec797def132ba59504
Reviewed-on: https://boringssl-review.googlesource.com/10260
Reviewed-by: Adam Langley <agl@google.com>
Commit-Queue: Adam Langley <agl@google.com>
CQ-Verified: CQ bot account: commit-bot@chromium.org <commit-bot@chromium.org>

If cert_cb runs asynchronously, we end up repeating a large part of very
stateful ClientHello processing. This seems to be mostly fine and there
are few users of server-side cert_cb (it's a new API in 1.0.2), but it's
a little scary.

This is also visible to external consumers because some callbacks get
called multiple times. We especially should try to avoid that as there
is no guarantee that these callbacks are idempotent and give the same
answer each time.

Change-Id: I212b2325eae2cfca0fb423dace101e466c5e5d4e
Reviewed-on: https://boringssl-review.googlesource.com/10224
Commit-Queue: David Benjamin <davidben@google.com>
Commit-Queue: Adam Langley <agl@google.com>
Reviewed-by: Adam Langley <agl@google.com>
CQ-Verified: CQ bot account: commit-bot@chromium.org <commit-bot@chromium.org>

Now that ssl_bytes_to_cipher_list is uninteresting, it can be an
implementation detail of ssl3_choose_cipher. This removes a tiny amount
of duplicated TLS 1.2 / TLS 1.3 code.

Change-Id: I116a6bb08bbc43da573d4b7b5626c556e1a7452d
Reviewed-on: https://boringssl-review.googlesource.com/10221
Reviewed-by: Adam Langley <agl@google.com>
Commit-Queue: David Benjamin <davidben@google.com>
CQ-Verified: CQ bot account: commit-bot@chromium.org <commit-bot@chromium.org>

It's odd that a function like ssl_bytes_to_cipher_list secretly has side
effects all over the place. This removes the need for the TLS 1.3 code
to re-query the version range, and it removes the requirement that the
RI extension be first.

Change-Id: Ic9af549db3aaa8880f3c591b8a13ba9ae91d6a46
Reviewed-on: https://boringssl-review.googlesource.com/10220
Reviewed-by: Adam Langley <agl@google.com>
Commit-Queue: David Benjamin <davidben@google.com>
CQ-Verified: CQ bot account: commit-bot@chromium.org <commit-bot@chromium.org>

Between TLS 1.2, TLS 1.3, and the early callback, we've got a lot of
ClientHello parsers. Unify everything on the early callback's parser. As
a side effect, this means we can parse a ClientHello fairly succinctly
from any function which will let us split up ClientHello states where
appropriate.

Change-Id: I2359b75f80926cc7d827570cf33f93029b39e525
Reviewed-on: https://boringssl-review.googlesource.com/10184
Reviewed-by: Adam Langley <agl@google.com>
Commit-Queue: Adam Langley <agl@google.com>
CQ-Verified: CQ bot account: commit-bot@chromium.org <commit-bot@chromium.org>

Only X509_up_ref left (it's still waiting on a few external callers).

BUG=89

Change-Id: Ia2aec2bb0a944356cb1ce29f3b58a26bdb8a9977
Reviewed-on: https://boringssl-review.googlesource.com/9141
Commit-Queue: David Benjamin <davidben@google.com>
Reviewed-by: Adam Langley <agl@google.com>

No sense in having it in both the 1.2 and 1.3 code.

Change-Id: Ib3854714afed24253af7f4bcee26d25e95a10211
Reviewed-on: https://boringssl-review.googlesource.com/9071
Reviewed-by: Adam Langley <agl@google.com>
Commit-Queue: Adam Langley <agl@google.com>
CQ-Verified: CQ bot account: commit-bot@chromium.org <commit-bot@chromium.org>

Extend the DTLS mock clock to apply to sessions too and test that
resumption behaves as expected.

Change-Id: Ib8fdec91b36e11cfa032872b63cf589f93b3da13
Reviewed-on: https://boringssl-review.googlesource.com/9110
Reviewed-by: Adam Langley <agl@google.com>
Commit-Queue: Adam Langley <agl@google.com>
CQ-Verified: CQ bot account: commit-bot@chromium.org <commit-bot@chromium.org>

Save a little bit of typing at the call site.

Change-Id: I818535409b57a694e5e0ea0e9741d89f2be89375
Reviewed-on: https://boringssl-review.googlesource.com/9090
Reviewed-by: Adam Langley <agl@google.com>

We will now send tickets as a server and accept them as a
client. Correctly offering and resuming them in the handshake will be
implemented in a follow-up.

Now that we're actually processing draft 14 tickets, bump the draft
version.

Change-Id: I304320a29c4ffe564fa9c00642a4ace96ff8d871
Reviewed-on: https://boringssl-review.googlesource.com/8982
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>

OpenSSL 1.1.0 added a function to tell if an SSL* is DTLS or not. This
is probably a good idea, especially since SSL_version returns
non-normalized versions.

BUG=91

Change-Id: I25c6cf08b2ebabf0c610c74691de103399f729bc
Reviewed-on: https://boringssl-review.googlesource.com/9077
Reviewed-by: Steven Valdez <svaldez@google.com>
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>

None of the SSL_VERIFY_FAIL_IF_NO_PEER_CERT codepaths will ever be
reached if SSL_VERIFY_PEER is unset. If we've gotten as far as getting a
Certificate message, consider SSL_VERIFY_FAIL_IF_NO_PEER_CERT alone
significant grounds for rejecting no peer certificate.

Change-Id: I2c6be4269d65b2467b86b1fc7d76ac47ca735553
Reviewed-on: https://boringssl-review.googlesource.com/9070
Reviewed-by: Adam Langley <agl@google.com>
Commit-Queue: Adam Langley <agl@google.com>
CQ-Verified: CQ bot account: commit-bot@chromium.org <commit-bot@chromium.org>

To prevent configuration/established session confusion, the handshake
session state is separated into the configured session (ssl->session)
and the newly created session (ssl->s3->new_session). Upon conclusion of
the handshake, the finalized session is stored
in (ssl->s3->established_session). During the handshake, any requests
for the session (SSL_get_session) return a non-resumable session, to
prevent resumption of a partially filled session. Sessions should only
be cached upon the completion of the full handshake, using the resulting
established_session. The semantics of accessors on the session are
maintained mid-renego.

Change-Id: I4358aecb71fce4fe14a6746c5af1416a69935078
Reviewed-on: https://boringssl-review.googlesource.com/8612
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>

With the previous DTLS change, the dispatch layer only cares about the
end of the handshake to know when to drop the current message. TLS 1.3
post-handshake messages will need a similar hook, so convert it to this
lower-level one.

BUG=83

Change-Id: I4c8c3ba55ba793afa065bf261a7bccac8816c348
Reviewed-on: https://boringssl-review.googlesource.com/8989
Reviewed-by: Adam Langley <agl@google.com>
Commit-Queue: Adam Langley <agl@google.com>
CQ-Verified: CQ bot account: commit-bot@chromium.org <commit-bot@chromium.org>

For TLS 1.3, we will need to process more complex post-handshake
messages. It is simplest if we use the same mechanism. In preparation,
allow ssl3_get_message to be called at any point.

Note that this stops reserving SSL3_RT_MAX_PLAIN_LENGTH in init_buf
right off the bat. Instead it will grow as-needed to accomodate the
handshake. SSL3_RT_MAX_PLAIN_LENGTH is rather larger than we probably
need to receive, particularly as a server, so this seems a good plan.

BUG=83

Change-Id: Id7f4024afc4c8a713b46b0d1625432315594350e
Reviewed-on: https://boringssl-review.googlesource.com/8985
Reviewed-by: Adam Langley <agl@google.com>
Commit-Queue: Adam Langley <agl@google.com>
CQ-Verified: CQ bot account: commit-bot@chromium.org <commit-bot@chromium.org>

It really should take a few more parameters and save a bit of
long-winded initialization work.

Change-Id: I2823f0aa82be39914a156323f6f32b470b6d6a3b
Reviewed-on: https://boringssl-review.googlesource.com/8876
Reviewed-by: Steven Valdez <svaldez@google.com>
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 adds the machinery for doing TLS 1.3 1RTT.

Change-Id: I736921ffe9dc6f6e64a08a836df6bb166d20f504
Reviewed-on: https://boringssl-review.googlesource.com/8720
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>

We already check for ciphers == NULL earlier in the function.

Change-Id: I0e676816d891e1d24cf45cab449c4d3915ec54ee
Reviewed-on: https://boringssl-review.googlesource.com/8815
Reviewed-by: Steven Valdez <svaldez@google.com>
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 allows us to implement custom RSA-PSS-based keys, so the async TLS
1.3 tests can proceed. For now, both sign and sign_digest exist, so
downstreams only need to manage a small change atomically. We'll remove
sign_digest separately.

In doing so, fold all the *_complete hooks into a single complete hook
as no one who implemented two operations ever used different function
pointers for them.

While I'm here, I've bumped BORINGSSL_API_VERSION. I do not believe we
have any SSL_PRIVATE_KEY_METHOD versions who cannot update atomically,
but save a round-trip in case we do. It's free.

Change-Id: I7f031aabfb3343805deee429b9e244aed5d76aed
Reviewed-on: https://boringssl-review.googlesource.com/8786
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 makes custom private keys and EVP_PKEYs symmetric again. There is
no longer a requirement that the caller pre-filter the configured
signing prefs.

Also switch EVP_PKEY_RSA to NID_rsaEncryption. These are identical, but
if some key types are to be NIDs, we should make them all NIDs.

Change-Id: I82ea41c27a3c57f4c4401ffe1ccad406783e4c64
Reviewed-on: https://boringssl-review.googlesource.com/8785
Reviewed-by: David Benjamin <davidben@google.com>

EVP_PKT_SIGN is redundant with the RSA/EC check which, in turn, is
redundant with sigalgs processing. The type need only be checked in the
pre-1.2 case which was indeed missing an else.

The client half was likewise missing an else, though it's unreachable
due to leaf cert checks.

Change-Id: Ib3550f71a2120b38eacdd671d4f1700876bcc485
Reviewed-on: https://boringssl-review.googlesource.com/8779
Reviewed-by: David Benjamin <davidben@google.com>

This is already duplicated between client and server and otherwise will
get duplicated yet again for TLS 1.3.

Change-Id: Ia8a352f9bc76fab0f88c1629d08a1da4c13d2510
Reviewed-on: https://boringssl-review.googlesource.com/8778
Reviewed-by: David Benjamin <davidben@google.com>

These will all want to be shared with the TLS 1.3 handshake.

Change-Id: I4e50dc0ed2295d43c7ae800015d71c1406311801
Reviewed-on: https://boringssl-review.googlesource.com/8776
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>

We must have mistranscribed this to CBB at some point. If the CA list is
empty, we must still include that field.

Change-Id: I341224d85c9073b09758517cdfa14893793ea0ec
Reviewed-on: https://boringssl-review.googlesource.com/8767
Commit-Queue: David Benjamin <davidben@google.com>
Reviewed-by: Nick Harper <nharper@chromium.org>
Reviewed-by: David Benjamin <davidben@google.com>

For now, skip the 1.2 -> 1.1 signal since that will affect shipping
code. We may as well enable it too, but wait until things have settled
down. This implements the version in draft-14 since draft-13's isn't
backwards-compatible.

Change-Id: I46be43e6f4c5203eb4ae006d1c6a2fe7d7a949ec
Reviewed-on: https://boringssl-review.googlesource.com/8724
Reviewed-by: David Benjamin <davidben@google.com>

ssl_verify_* already ought to be checking this, so there's only a need
to check against the configured preferences.

Change-Id: I79bc771969c57f953278e622084641e6e20108e3
Reviewed-on: https://boringssl-review.googlesource.com/8698
Reviewed-by: David Benjamin <davidben@google.com>

Rather than blindly select SHA-1 if we can't find a matching one, act as
if the peer advertised rsa_pkcs1_sha1 and ecdsa_sha1. This means that we
will fail the handshake if no common algorithm may be found.

This is done in preparation for removing the SHA-1 default in TLS 1.3.

Change-Id: I3584947909d3d6988b940f9404044cace265b20d
Reviewed-on: https://boringssl-review.googlesource.com/8695
Reviewed-by: David Benjamin <davidben@google.com>

Instead have ssl3_cert_verify_hash output the hash, since it already
knows it. Also add a missing EVP_PKEY_CTX_set_signature_md call on the
client half. (Although, the call isn't actually necessary.)

Also remove now unnecessary static assert. Since EVP_md5_sha1 is an
EVP_MD itself, EVP_MAX_MD_SIZE is required to fit it already.

Change-Id: Ief74fdbdf08e9f124679475bafba2f6f1d8fc687
Reviewed-on: https://boringssl-review.googlesource.com/8692
Reviewed-by: Steven Valdez <svaldez@google.com>
Reviewed-by: David Benjamin <davidben@google.com>

It still places the current message all over the place, but remove the
bizarre init_num/error/ok split. Now callers get the message length out
of init_num, which mirrors init_msg. Also fix some signedness.

Change-Id: Ic2e97b6b99e234926504ff217b8aedae85ba6596
Reviewed-on: https://boringssl-review.googlesource.com/8690
Reviewed-by: David Benjamin <davidben@google.com>

This machinery is so different between TLS and DTLS that there is no
sense in having them share structures. This switches us to maintaining
the full reassembled message in hm_fragment and get_message just lets
the caller read out of that when ready.

This removes the last direct handshake dependency on init_buf,
ssl3_hash_message.

Change-Id: I4eccfb6e6021116255daead5359a0aa3f4d5be7b
Reviewed-on: https://boringssl-review.googlesource.com/8667
Reviewed-by: Steven Valdez <svaldez@google.com>
Reviewed-by: David Benjamin <davidben@google.com>

Both DTLS and TLS still use it, but that will change in the following
commit. This also removes the handshake's knowledge of the
dtls_clear_incoming_messages function.

(It's possible we'll want to get rid of begin_handshake in favor of
allocating it lazily depending on how TLS 1.3 post-handshake messages
end up working out. But this should work for now.)

Change-Id: I0f512788bbc330ab2c947890939c73e0a1aca18b
Reviewed-on: https://boringssl-review.googlesource.com/8666
Reviewed-by: Steven Valdez <svaldez@google.com>
Reviewed-by: David Benjamin <davidben@google.com>

V2ClientHello is going to be ugly wherever we do it, but this hides it
behind the transport method table. It removes a place where the
handshake state machine reaches into ssl3_get_message's internal state.
ssl3_get_message will now silently translate V2ClientHellos into true
ClientHellos and manage the handshake hash appropriately.

Now the only accesses of init_buf from the handshake state machines are
to create and destroy the buffer.

Change-Id: I81467a038f6ac472a465eec7486a443fe50a98e1
Reviewed-on: https://boringssl-review.googlesource.com/8641
Reviewed-by: Adam Langley <agl@google.com>

Rather than have a separate codepath, just skip the message_complete
logic and parse what's in the buffer. This also cuts down on one input
to setting up a reuse_message; message_type is now only written to in
the get_message implementation.

Change-Id: I96689b5957a3f2548af9099ec4e53cabacdc395a
Reviewed-on: https://boringssl-review.googlesource.com/8640
Reviewed-by: Steven Valdez <svaldez@google.com>
Reviewed-by: Adam Langley <agl@google.com>

To match the Go side. That message will never be used for anything else,
so there's not much need to give it such a long name.

Change-Id: I3396c9d513d02d873e59cd8e81ee64005c5c706c
Reviewed-on: https://boringssl-review.googlesource.com/8620
Reviewed-by: Steven Valdez <svaldez@google.com>
Reviewed-by: David Benjamin <davidben@google.com>

In order to delay the digest of the handshake transcript and unify
around message-based signing callbacks, a copy of the transcript is kept
around until we are sure there is no certificate authentication.

This removes support for SSL_PRIVATE_KEY_METHOD as a client in SSL 3.0.

Change-Id: If8999a19ca021b4ff439319ab91e2cd2103caa64
Reviewed-on: https://boringssl-review.googlesource.com/8561
Reviewed-by: David Benjamin <davidben@google.com>

We ended up switching this from a curve to a cipher suite, so the group
ID isn't used. This is in preparation for adding an API for the curve
ID, at which point leaving the protocol constants undefined seems
somewhat bad manners.

Change-Id: Icb8bf4594879dbbc24177551868ecfe89bc2f8c3
Reviewed-on: https://boringssl-review.googlesource.com/8563
Reviewed-by: Adam Langley <agl@google.com>

OpenSSL's SSL_OP_NO_* flags allow discontinuous version ranges. This is a
nuisance for two reasons. First it makes it unnecessarily difficult to answer
"are any versions below TLS 1.3 enabled?". Second the protocol does not allow
discontinuous version ranges on the client anyway. OpenSSL instead picks the
first continous range of enabled versions on the client, but not the server.

This is bizarrely inconsistent. It also doesn't quite do this as the
ClientHello sending logic does this, but not the ServerHello processing logic.
So we actually break some invariants slightly. The logic is also cumbersome in
DTLS which kindly inverts the comparison logic.

First, switch min_version/max_version's storage to normalized versions. Next
replace all the ad-hoc version-related functions with a single
ssl_get_version_range function. Client and server now consistently pick a
contiguous range of versions. Note this is a slight behavior change for
servers. Version-range-sensitive logic is rewritten to use this new function.

BUG=66

Change-Id: Iad0d64f2b7a917603fc7da54c9fc6656c5fbdb24
Reviewed-on: https://boringssl-review.googlesource.com/8513
Reviewed-by: David Benjamin <davidben@google.com>

The signing logic itself still depends on pre-hashed messages and will be fixed
in later commits.

Change-Id: I901b0d99917c311653d44efa34a044bbb9f11e57
Reviewed-on: https://boringssl-review.googlesource.com/8545
Reviewed-by: David Benjamin <davidben@google.com>

They're not necessary.

Change-Id: Ifeb3fae73a8b22f88019e6ef9f9ba5e64ed3cfab
Reviewed-on: https://boringssl-review.googlesource.com/8543
Reviewed-by: David Benjamin <davidben@google.com>

As part of the SignatureAlgorithm change in the TLS 1.3 specification,
the existing signature/hash combinations are replaced with a combined
signature algorithm identifier. This change maintains the existing APIs
while fixing the internal representations. The signing code currently
still treats the SignatureAlgorithm as a decomposed value, which will be
fixed as part of a separate CL.

Change-Id: I0cd1660d74ad9bcf55ce5da4449bf2922660be36
Reviewed-on: https://boringssl-review.googlesource.com/8480
Reviewed-by: Steven Valdez <svaldez@google.com>
Reviewed-by: David Benjamin <davidben@google.com>

This allows us to use CBB for all handshake messages. Now, SSL_PROTOCOL_METHOD
is responsible for implementing a trio of CBB-related hooks to assemble
handshake messages.

Change-Id: I144d3cac4f05b6637bf45d3f838673fc5c854405
Reviewed-on: https://boringssl-review.googlesource.com/8440
Reviewed-by: Adam Langley <agl@google.com>

It has size 7. There's no need for a priority queue structure, especially one
that's O(N^2) anyway.

Change-Id: I7609794aac1925c9bbf3015744cae266dcb79bff
Reviewed-on: https://boringssl-review.googlesource.com/8437
Reviewed-by: Adam Langley <agl@google.com>

The pair was a remnant of some weird statefulness and also ChangeCipherSpec
having a "sequence number" to make the pqueue turn into an array.

Change-Id: Iffd82594314df43934073bd141faee0fc167ed5f
Reviewed-on: https://boringssl-review.googlesource.com/8436
Reviewed-by: Adam Langley <agl@google.com>

Post-handshake retransmit in DTLS no longer needs that scratch space.

Change-Id: I2f070675d72426e61b19dab5bcac40bf62b8fd8d
Reviewed-on: https://boringssl-review.googlesource.com/8434
Reviewed-by: Adam Langley <agl@google.com>

It is an explicit copy of something, but it's a lot easier to reason about than
the init_buf/init_num gynmastics we were previously doing. This is along the
way to getting init_buf out of here.

Change-Id: Ia1819ba9db60ef6db09dd60d208dbc95fcfb4bd2
Reviewed-on: https://boringssl-review.googlesource.com/8432
Reviewed-by: Adam Langley <agl@google.com>