commit 26f186bcabd9fe8221f6c732d13118120315a1f5
author David Benjamin <davidben@google.com> Tue Jun 08 19:17:58 2021 -0400
committer Adam Langley <agl@google.com> Wed Jun 09 18:14:19 2021 +0000
tree 2efea2ec5d14406a7839b7cad45059ef3214edad
parent 7fffa4636cf7647daf981914286d5d32f1beab6d

Implement a handshake hint for certificate compression.

While decompression is deterministic, compression is not. New revisions
of the compression algorithm may start using different (hopefully
smaller!) compressions. So this doesn't cause hint mismatches, add a
certificate compression hint. If the shim's Certificate message matches
the handshaker, we'll reuse the already compressed message.

This also adds what appears to be a missing test for when the server
cannot find compression algorithms in common.

Change-Id: Idbedaceb20208463d8f61581ee27971c17fcd126
Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/48005
Reviewed-by: Adam Langley <agl@google.com>

ssl/tls13_both.cc

diff --git a/ssl/tls13_both.cc b/ssl/tls13_both.cc
index 5837187..0354f39 100644
--- a/ssl/tls13_both.cc
+++ b/ssl/tls13_both.cc
@@ -534,9 +534,37 @@
                                  SSL3_MT_COMPRESSED_CERTIFICATE) ||
       !CBB_add_u16(body, hs->cert_compression_alg_id) ||
       !CBB_add_u24(body, msg.size()) ||
-      !CBB_add_u24_length_prefixed(body, &compressed) ||
-      !alg->compress(ssl, &compressed, msg.data(), msg.size()) ||
-      !ssl_add_message_cbb(ssl, cbb.get())) {
+      !CBB_add_u24_length_prefixed(body, &compressed)) {
+    OPENSSL_PUT_ERROR(SSL, ERR_R_INTERNAL_ERROR);
+    return false;
+  }
+
+  SSL_HANDSHAKE_HINTS *const hints = hs->hints.get();
+  if (hints && !hs->hints_requested &&
+      hints->cert_compression_alg_id == hs->cert_compression_alg_id &&
+      hints->cert_compression_input == MakeConstSpan(msg) &&
+      !hints->cert_compression_output.empty()) {
+    if (!CBB_add_bytes(&compressed, hints->cert_compression_output.data(),
+                       hints->cert_compression_output.size())) {
+      OPENSSL_PUT_ERROR(SSL, ERR_R_INTERNAL_ERROR);
+      return false;
+    }
+  } else {
+    if (!alg->compress(ssl, &compressed, msg.data(), msg.size())) {
+      OPENSSL_PUT_ERROR(SSL, ERR_R_INTERNAL_ERROR);
+      return false;
+    }
+    if (hints && hs->hints_requested) {
+      hints->cert_compression_alg_id = hs->cert_compression_alg_id;
+      if (!hints->cert_compression_input.CopyFrom(msg) ||
+          !hints->cert_compression_output.CopyFrom(
+              MakeConstSpan(CBB_data(&compressed), CBB_len(&compressed)))) {
+        return false;
+      }
+    }
+  }
+
+  if (!ssl_add_message_cbb(ssl, cbb.get())) {
     OPENSSL_PUT_ERROR(SSL, ERR_R_INTERNAL_ERROR);
     return false;
   }