IJHack / QtPass / 35589605901

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Commit Message

Signed .gpg-id: refuse a rollback to an older generation (#1869)

* Signed .gpg-id: refuse a rollback to an older generation

A signature proves that a recipient list is authentic and unmodified, not
that it is the current one. Whoever can write to a shared store can put
back an older, genuinely signed list that still names a member since
removed, and every later Insert and re-encryption would encrypt to them
again. pass has the same property; QtPass inherited the model with the
signing feature.

Every .gpg-id QtPass writes (ImitatePass::writeGpgIdFile,
ProfileInit::writeGpgId, Pass::seedGpgIdFile) now starts with one comment
line, "# QtPass-GpgId-Generation: N", that pass and Pass::parseRecipients
ignore and the signature covers. GpgIdGeneration keeps, per .gpg-id
(keyed by a SHA-256 of its canonical path, in a settings file of its own
with fallbacks off), the highest generation this device has accepted or
written, written through with sync() before it counts. With signing on,
loadVerifiedRecipients() refuses a verified list whose generation is lower
than that, with a message naming both numbers and the way through (save
the recipients again, which writes one above). The parser is strict: no
line is generation 0 (a list from pass or from before), exactly one
well-formed line is its number, a malformed or duplicated line makes the
list unusable rather than 0, so parser ambiguity is not a downgrade.

What it is not, stated in SECURITY.md: freshness for a device that never
saw the newer list (first sight, or offline for the change) is out of
reach without a server; the generation is monotonic per device, two
devices can both produce the same next one and Git resolves that; the pass
backend's pass reads the list itself.

Tests: a new tst_gpgidgeneration suite (grammar, key canonicalisation,
accept/remember/next, write-through), an end-to-end rollback in
tst_imitatepass with the signing fake gpg (generation 1 with Bob,
generation 2 without, the generation... (continued)

Coverage Stats

202 of 211 new or added lines in 4 files covered. (95.73%)

9 existing lines in 1 file now uncovered.

7221 of 9156 relevant lines covered (78.87%)

75.85 hits per line