Implement Verifiable Advertiser Conversions for Brave Ads

[moritzhaller]

Resolves brave/brave-browser#13368

Submitter Checklist:

• There is a ticket for my issue.
• Used Github auto-closing keywords in the commit message.
• Wrote a good PR/commit description
• Added appropriate labels (QA/Yes or QA/No; release-notes/include or release-notes/exclude; OS/...) to the associated issue
• Checked the PR locally: npm run test -- brave_browser_tests, npm run test -- brave_unit_tests, npm run lint, npm run gn_check, npm run tslint
• Ran git rebase master (if needed).
• Requested a security/privacy review as needed.

Reviewer Checklist:

• New files have MPL-2.0 license header.
• Adequate test coverage exists to prevent regressions
• Major classes, functions and non-trivial code blocks are well-commented
• Changes in component dependencies are properly reflected in gn
• Code follows the style guide
• Test plan is specified in PR before merging

After-merge Checklist:

• The associated issue milestone is set to the smallest version that the
  changes has landed on.
• All relevant documentation has been updated, for instance:
  • https://github.com/brave/brave-browser/wiki/Deviations-from-Chromium-(features-we-disable-or-remove)
  • https://github.com/brave/brave-browser/wiki/Proxy-redirected-URLs
  • https://github.com/brave/brave-browser/wiki/Fingerprinting-Protections
  • https://github.com/brave/brave-browser/wiki/Brave%E2%80%99s-Use-of-Referral-Codes
  • https://github.com/brave/brave-browser/wiki/Custom-Headers
  • https://github.com/brave/brave-browser/wiki/Web-Compatibility-Exceptions-in-Brave
  • https://github.com/brave/brave-browser/wiki/QA-Guide
  • https://github.com/brave/brave-browser/wiki/P3A

Test Plan:

0. start browser on fresh profile with npm start -- --enable-logging=stderr --vmodule="*/bat-native-ads/*"=6,"*/brave_ads/*"=6,"*/brave_user_model/*"=6,"*/bat_ads/*"=6 --brave-ads-staging --rewards=staging=true --brave-ads-debug

1. run test site with conversion tag (e.g. <meta name="ad-conversion-id" content="smartbrownfoxes42">) on localhost:8000

2. add test "untargeted" ad with conversion ID and test key to catalog and inject via proxy, e.g.

 "conversions": [
            {
              "type": "postview",
              "urlPattern": "http://localhost:8000/*",
              "observationWindow": 1,
              "conversionPublicKey": "ofIveUY/bM7qlL9eIkAv/xbjDItFs1xRTTYKRZZsPHI="
            }
          ]

3. trigger add of segment "untargeted"

4. navigate to localhost:8000 and verify that a conversion was triggered with logs

[86997:775:0216/065612.681696:VERBOSE1:conversions.cc(412)] Convert creative instance id 4983dc92-09fd-4e5c-94c3-616a4728c1d9 and creative set id 5bdeab83-048f-48a7-9602-a1092ded123c in 0 hours, 3 minutes, 57 seconds at 07:00
[86997:775:0216/065612.684147:VERBOSE6:conversions.cc(306)] Successfully logged conversion event

5. wait until the confirmation for the conversion event is triggered (time in log above) and verify "envelope" payload via proxy

"envelope": {
"alg": "alg_placeholder",
"ciphertext": "ciphertext_placeholder",
"epk": "epk_placeholder",
"nonce": "nonce_placeholder"
},

6. Verify that payload can be decrypted via https://github.com/brave-experiments/VAC-Encryption-Envelopes/blob/main/src/advertiser.ts

[diracdeltas]

@moritzhaller please open a security review for this when it's ready, thx

[orspetol]

@moritzhaller A note on seeds in this library: Technically TweetNaCL allows you to "pre-seed" if you want; however, I want to avoid this as much as possible to prevent implementors downstream from incorrectly seeding (just let the library call Random).

[moritzhaller]

@moritzhaller A note on seeds in this library: Technically TweetNaCL allows you to "pre-seed" if you want; however, I want to avoid this as much as possible to prevent implementors downstream from incorrectly seeding (just let the library call Random).

@orspetol totally agree for future implementations, and as discussed we need to keep the seed in the utils for now to ensure key parity between ads and rewards.

[tmancey]

LGTM++

[kylehickinson]

iOS lgtm

[orspetol]

LGTM

[tmancey]

CI failed due to known audit deps