[Nearby] Rename advertisement field.

chrome/services/sharing/nearby/decoder/nearby_decoder_unittest.cc
chrome/browser/nearby_sharing/nearby_sharing_service_impl.cc
- Update usage of advertisement field to new name

chrome/services/sharing/public/*
- Rename advertisement field to be more accurate
- Update comments to be more detailed

This is a follow-on to feedback raised on
Ia384e12083a590f52beb1f98d50b192ab20f31cd

Bug: 1084582

Change-Id: If5a3c40ee0ad33de01bd5c4322078c4fa9b206c1
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2352893Reviewed-by: Alex Chau <alexchau@chromium.org>
Reviewed-by: Richard Knoll <knollr@chromium.org>
Reviewed-by: Alex Gough <ajgo@chromium.org>
Reviewed-by: Josh Nohle <nohle@chromium.org>
Commit-Queue: Naomi Musgrave <nmusgrave@chromium.org>
Cr-Commit-Position: refs/heads/master@{#797687}

chrome/browser/nearby_sharing/nearby_sharing_service_impl.cc

@@ -567,11 +567,12 @@ void NearbySharingServiceImpl::OnOutgoingAdvertisementDecoded(
 
   // Once get the advertisement, the first thing to do is decrypt the
   // certificate.
-  std::vector<uint8_t> encrypted_metadata = advertisement->encrypted_metadata;
+  std::vector<uint8_t> encrypted_metadata_key =
+      advertisement->encrypted_metadata_key;
   std::vector<uint8_t> salt = advertisement->salt;
 
   GetCertificateManager()->GetDecryptedPublicCertificate(
-      std::move(encrypted_metadata), std::move(salt),
+      std::move(encrypted_metadata_key), std::move(salt),
       base::BindOnce(&NearbySharingServiceImpl::OnOutgoingDecryptedCertificate,
                      weak_ptr_factory_.GetWeakPtr(), endpoint_id,
                      std::move(advertisement)));
@@ -1334,11 +1335,12 @@ void NearbySharingServiceImpl::OnIncomingAdvertisementDecoded(
     return;
   }
 
-  std::vector<uint8_t> encrypted_metadata = advertisement->encrypted_metadata;
+  std::vector<uint8_t> encrypted_metadata_key =
+      advertisement->encrypted_metadata_key;
   std::vector<uint8_t> salt = advertisement->salt;
 
   GetCertificateManager()->GetDecryptedPublicCertificate(
-      std::move(encrypted_metadata), std::move(salt),
+      std::move(encrypted_metadata_key), std::move(salt),
       base::BindOnce(&NearbySharingServiceImpl::OnIncomingDecryptedCertificate,
                      weak_ptr_factory_.GetWeakPtr(), endpoint_id, connection,
                      std::move(advertisement)));

chrome/services/sharing/nearby/decoder/nearby_decoder_unittest.cc

@@ -36,7 +36,7 @@ void ExpectEquals(const Advertisement& self,
                   const mojom::AdvertisementPtr& other) {
   EXPECT_EQ(self.device_name(), other->device_name);
   EXPECT_EQ(self.salt(), other->salt);
-  EXPECT_EQ(self.encrypted_metadata_key(), other->encrypted_metadata);
+  EXPECT_EQ(self.encrypted_metadata_key(), other->encrypted_metadata_key);
 }
 
 void ExpectFrameContainsIntroduction(

chrome/services/sharing/public/cpp/advertisement.h

@@ -56,11 +56,14 @@ class Advertisement {
   // ways of parsing the endpoint id.
   int version_;
 
-  // A randomized salt used in the hash of the account identifier.
+  // Random bytes that were used as salt during encryption of public certificate
+  // metadata.
   std::vector<uint8_t> salt_;
 
-  // A salted hash of an account identifier that signifies who the remote device
-  // is.
+  // An encrypted symmetric key that was used to encrypt public certificate
+  // metadata, including an account identifier signifying the remote device.
+  // The key can be decrypted using |salt| and the corresponding public
+  // certificate's secret/authenticity key.
   std::vector<uint8_t> encrypted_metadata_key_;
 
   // The human readable name of the remote device.

chrome/services/sharing/public/mojom/nearby_decoder_types.mojom

@@ -8,11 +8,14 @@ import "mojo/public/mojom/base/time.mojom";
 
 // An advertisement send by a device in receiving mode.
 struct Advertisement {
-  // Random data erived from a device's private key.
+  // Random bytes that were used as salt during encryption of public
+  // certificate metadata.
   array<uint8, 2> salt;
 
-  // Derived from a device's private key. Identifying data for the device.
-  array<uint8, 14> encrypted_metadata;
+  // An encrypted symmetric key that was used to encrypt public certificate
+  // metadata. The key can be decrypted using |salt| and the corresponding
+  // public certificate's secret/authenticity key.
+  array<uint8, 14> encrypted_metadata_key;
 
   // If present, the device is visible to everyone rather than contacts only.
   string? device_name;