We do :) The full details are at https://github.com/mozilla/fxa-auth-server/wiki/onepw-protoc..., but basically we derive two separate keys: one for authentication, that gets sent over the wire, and a completely different one for decrypting the sync key, which is not set over the wire. This means that even if you can observe the entire transaction, you still aren't able to derive the decryption key.
It's more or less:
let quickStretchPW = PBKDF2(email, password)
let authPW = HKDF('authPW', quickStretchPW)
let unwrapBkey = HKDF('unwrapBkey', quickStretchPW)
Where unwrapBkey !== authPW.
In Firefox 57.0 Releasedmozilla
fxa-auth-server
JavaScript2014–2023
mozilla / fxa-auth-server · Archived
fxa-auth-server
DEPRECATED - Migrated to https://github.com/mozilla/fxa
19Distinct people
19Mentions
0Explicit recommenders
397GitHub stars
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What it is
DEPRECATED - Migrated to https://github.com/mozilla/fxa
GitHub
Where it is used
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This week on Hacker News
Nov 7–Nov 14 UTC · Direct repository links and separately labeled related project stories. Indexed through 11/14/2026, 6:01:08 PM UTC.
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HN mentions by year19 dated mentions
Observed mentions: 2014-02-03 10:59:41 UTC to 2023-11-24 08:48:06 UTC.
Counts come from the repository’s dated source evidence. Index cutoff: 2026-11-02 08:16:59 UTC.
View mention counts and date ranges
| Period | Start (UTC) | End (exclusive, UTC) | Mentions | Submissions | Comments |
|---|---|---|---|---|---|
| 2014 | 2014-01-01 00:00:00 UTC | 2015-01-01 00:00:00 UTC | 10 | 3 | 7 |
| 2015 | 2015-01-01 00:00:00 UTC | 2016-01-01 00:00:00 UTC | 1 | 0 | 1 |
| 2016 | 2016-01-01 00:00:00 UTC | 2017-01-01 00:00:00 UTC | 1 | 0 | 1 |
| 2017 | 2017-01-01 00:00:00 UTC | 2018-01-01 00:00:00 UTC | 1 | 0 | 1 |
| 2018 | 2018-01-01 00:00:00 UTC | 2019-01-01 00:00:00 UTC | 4 | 0 | 4 |
| 2019 | 2019-01-01 00:00:00 UTC | 2020-01-01 00:00:00 UTC | 0 | 0 | 0 |
| 2020 | 2020-01-01 00:00:00 UTC | 2021-01-01 00:00:00 UTC | 0 | 0 | 0 |
| 2021 | 2021-01-01 00:00:00 UTC | 2022-01-01 00:00:00 UTC | 1 | 0 | 1 |
| 2022 | 2022-01-01 00:00:00 UTC | 2023-01-01 00:00:00 UTC | 0 | 0 | 0 |
| 2023 | 2023-01-01 00:00:00 UTC | 2024-01-01 00:00:00 UTC | 1 | 0 | 1 |
From the project README
An excerpt from the repository, fetched Nov 13, 2026.
Read the project’s introduction
This repository has been migrated to https://github.com/mozilla/fxa/tree/master/packages/fxa-auth-server
Please file issues and open pull requests against https://github.com/mozilla/fxa
Read the full README on GitHub