Add most of an ECH client implementation.
Based on an initial implementation by Dan McArdle at
https://boringssl-review.googlesource.com/c/boringssl/+/46784
This CL contains most of a client implementation for
draft-ietf-tls-esni-10. The pieces missing so far, which will be done in
follow-up CLs are:
1. While the ClientHelloInner is padded, the server Certificate message
is not. I'll add that once we resolve the spec discussions on how to
do that. (We were originally going to use TLS record-level padding,
but that doesn't work well with QUIC.)
2. The client should check the public name is a valid DNS name before
copying it into ClientHelloOuter.server_name.
3. The ClientHelloOuter handshake flow is not yet implemented. This CL
can detect when the server selects ClientHelloOuter, but for now the
handshake immediately fails. A follow-up CL will remove that logic
and instead add the APIs and extra checks needed.
Otherwise, this should be complete, including padding and compression.
The main interesting point design-wise is that we run through
ClientHello construction multiple times. We need to construct
ClientHelloInner and ClientHelloOuter. Then each of those has slight
variants: EncodedClientHelloInner is the compressed form, and
ClientHelloOuterAAD just has the ECH extension erased to avoid a
circular dependency.
I've computed ClientHelloInner and EncodedClientHelloInner concurrently
because the compression scheme requires shifting the extensions around
to be contiguous. However, I've computed ClientHelloOuterAAD and
ClientHelloOuter by running through the logic twice. This probably can
be done better, but the next draft revises the construction anyway, so
I'm thinking I'll rework it then. (In the next draft, we use a
placeholder payload of the same length, so we can construct the
ClientHello once and fill in the payload.)
Additionally, now that we have a client available in ssl_test, this adds
a threading test to confirm that SSL_CTX_set1_ech_keys is properly
synchronized. (Confirmed that, if I drop the lock in
SSL_CTX_set1_ech_keys, TSan notices.)
Change-Id: Icaff68b595035bdcc73c468ff638e67c84239ef4
Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/48004
Reviewed-by: Adam Langley <agl@google.com>
diff --git a/ssl/tls13_server.cc b/ssl/tls13_server.cc
index c772010..7f32b6c 100644
--- a/ssl/tls13_server.cc
+++ b/ssl/tls13_server.cc
@@ -512,17 +512,12 @@
ssl_get_handshake_digest(ssl_protocol_version(ssl), hs->new_cipher));
// Set up the key schedule and incorporate the PSK into the running secret.
- if (ssl->s3->session_reused) {
- if (!tls13_init_key_schedule(
- hs, MakeConstSpan(hs->new_session->secret,
- hs->new_session->secret_length))) {
- return ssl_hs_error;
- }
- } else if (!tls13_init_key_schedule(hs, MakeConstSpan(kZeroes, hash_len))) {
- return ssl_hs_error;
- }
-
- if (!ssl_hash_message(hs, msg)) {
+ if (!tls13_init_key_schedule(
+ hs, ssl->s3->session_reused
+ ? MakeConstSpan(hs->new_session->secret,
+ hs->new_session->secret_length)
+ : MakeConstSpan(kZeroes, hash_len)) ||
+ !ssl_hash_message(hs, msg)) {
return ssl_hs_error;
}
@@ -730,28 +725,6 @@
return ssl_hs_ok;
}
-static bool make_server_hello(SSL_HANDSHAKE *hs, Array<uint8_t> *out) {
- SSL *const ssl = hs->ssl;
- ScopedCBB cbb;
- CBB body, extensions, session_id;
- if (!ssl->method->init_message(ssl, cbb.get(), &body, SSL3_MT_SERVER_HELLO) ||
- !CBB_add_u16(&body, TLS1_2_VERSION) ||
- !CBB_add_bytes(&body, ssl->s3->server_random,
- sizeof(ssl->s3->server_random)) ||
- !CBB_add_u8_length_prefixed(&body, &session_id) ||
- !CBB_add_bytes(&session_id, hs->session_id, hs->session_id_len) ||
- !CBB_add_u16(&body, SSL_CIPHER_get_protocol_id(hs->new_cipher)) ||
- !CBB_add_u8(&body, 0) ||
- !CBB_add_u16_length_prefixed(&body, &extensions) ||
- !ssl_ext_pre_shared_key_add_serverhello(hs, &extensions) ||
- !ssl_ext_key_share_add_serverhello(hs, &extensions) ||
- !ssl_ext_supported_versions_add_serverhello(hs, &extensions) ||
- !ssl->method->finish_message(ssl, cbb.get(), out)) {
- return false;
- }
- return true;
-}
-
static enum ssl_hs_wait_t do_send_server_hello(SSL_HANDSHAKE *hs) {
SSL *const ssl = hs->ssl;
@@ -769,24 +742,44 @@
}
}
- assert(!ssl->s3->ech_accept || hs->ech_is_inner_present);
- if (hs->ech_is_inner_present) {
- // Construct the ServerHelloECHConf message, which is the same as
- // ServerHello, except the last 8 bytes of its random field are zeroed out.
- Span<uint8_t> random_suffix = random.subspan(24);
- OPENSSL_memset(random_suffix.data(), 0, random_suffix.size());
-
- Array<uint8_t> server_hello_ech_conf;
- if (!make_server_hello(hs, &server_hello_ech_conf) ||
- !tls13_ech_accept_confirmation(hs, random_suffix,
- server_hello_ech_conf)) {
- return ssl_hs_error;
- }
+ Array<uint8_t> server_hello;
+ ScopedCBB cbb;
+ CBB body, extensions, session_id;
+ if (!ssl->method->init_message(ssl, cbb.get(), &body, SSL3_MT_SERVER_HELLO) ||
+ !CBB_add_u16(&body, TLS1_2_VERSION) ||
+ !CBB_add_bytes(&body, ssl->s3->server_random,
+ sizeof(ssl->s3->server_random)) ||
+ !CBB_add_u8_length_prefixed(&body, &session_id) ||
+ !CBB_add_bytes(&session_id, hs->session_id, hs->session_id_len) ||
+ !CBB_add_u16(&body, SSL_CIPHER_get_protocol_id(hs->new_cipher)) ||
+ !CBB_add_u8(&body, 0) ||
+ !CBB_add_u16_length_prefixed(&body, &extensions) ||
+ !ssl_ext_pre_shared_key_add_serverhello(hs, &extensions) ||
+ !ssl_ext_key_share_add_serverhello(hs, &extensions) ||
+ !ssl_ext_supported_versions_add_serverhello(hs, &extensions) ||
+ !ssl->method->finish_message(ssl, cbb.get(), &server_hello)) {
+ return ssl_hs_error;
}
- Array<uint8_t> server_hello;
- if (!make_server_hello(hs, &server_hello) ||
- !ssl->method->add_message(ssl, std::move(server_hello))) {
+ assert(!ssl->s3->ech_accept || hs->ech_is_inner_present);
+ if (hs->ech_is_inner_present) {
+ // Fill in the ECH confirmation signal.
+ Span<uint8_t> random_suffix =
+ random.subspan(SSL3_RANDOM_SIZE - ECH_CONFIRMATION_SIGNAL_LEN);
+ if (!ssl_ech_accept_confirmation(hs, random_suffix, hs->transcript,
+ server_hello)) {
+ return ssl_hs_error;
+ }
+
+ // Update |server_hello|.
+ const size_t offset = ssl_ech_confirmation_signal_hello_offset(ssl);
+ Span<uint8_t> server_hello_out =
+ MakeSpan(server_hello).subspan(offset, ECH_CONFIRMATION_SIGNAL_LEN);
+ OPENSSL_memcpy(server_hello_out.data(), random_suffix.data(),
+ ECH_CONFIRMATION_SIGNAL_LEN);
+ }
+
+ if (!ssl->method->add_message(ssl, std::move(server_hello))) {
return ssl_hs_error;
}
@@ -805,8 +798,6 @@
}
// Send EncryptedExtensions.
- ScopedCBB cbb;
- CBB body;
if (!ssl->method->init_message(ssl, cbb.get(), &body,
SSL3_MT_ENCRYPTED_EXTENSIONS) ||
!ssl_add_serverhello_tlsext(hs, &body) ||
