Replaces `ac.cord.auxiliary.frost.dkg.chill.ChillDkg` with
`fr.acinq.bitcoin.crypto.dkg.chill.ChillDKG` throughout ChillDkgRitualManager.
The implementation being dropped says what it is in its own header:
WARNING: This code is slow and not hardened against side channel attacks. Do
not use for anything but tests.
It is a 1090-line "Reference port of ChillDKG (chilldkg_ref/chilldkg.py)" doing
BigInteger arithmetic through ac.cord.auxiliary.cryptography's Scalar and
GroupElement, with no call into libsecp256k1 anywhere in the file.
secp256k1-frost-kmp's own KNOWN_ISSUES.md confirms the constant-time
libsecp256k1 backing is used only for hashing. Real key material was being
generated by it.
The replacement is 438 lines in which every operation delegates to
`Secp256k1.chilldkg*` -- the constant-time C from the secp256k1-zkp fork the
submodule chain compiles. This is an improvement, not a clean bill of health: that
module carries its own "experimental and must not be used in production" warning.
It is constant-time C instead of variable-time Kotlin, which is the part that
mattered.
Three things changed shape rather than just types.
SessionParams no longer exists. ChillDKG takes the host public keys and the
threshold at every call and hashes them into the session identity itself, so
`sessionParams()` becomes `hostPublicKeys()` returning List<PublicKey>, and the
threshold rides along on the session row. That removed a parameter from four
signatures.
Faults are values now, not exceptions. ChillDKG reports a faulty participant as a
ChilldkgFault field on each result because it is a normal outcome of a DKG rather
than a bug. This ritual has exactly one response to all of them -- the key is
unusable, so the session dies and the group is told -- so `raiseIfFaulty` turns
them into an exception and lets them join advance()'s existing single failure
path. The gain is in the failure text: the reason shown to the group goes from
whatever `e.message` happened to hold to "ChillDKG round 2 failed: a participant
is faulty (participant 3)". On a failed DKG, which participant to blame is the
only actionable thing there is.
Two recomputes got names. The old code inlined a second participantStep1 call to
rebuild state1 for participantStep2, and rebuilt coordinator state separately in
aggregateRound2. Those are now `participantState1()` and `coordinatorStep1()`, the
latter carrying the fault check so both of its callers get it. The
recompute-rather-than-store design is kept deliberately: ChillDKG's states are
serializable and could be persisted, but they are pure functions of inputs the
DkgSession row already holds, so storing them would mean a schema change and a
Room migration for no behavioural gain. That reasoning is now in the kdoc.
Also drops an unused hostSeckey parameter from aggregateRound2, whose signature
was changing anyway, and updates doc comments in DkgRitualEvents, DkgSession and
DkgThresholdTag that named types which no longer exist -- ChillDkg.ParticipantMsg1
and friends -- to the protocol's own names: pmsg1, cmsg1, CertEq signature,
certificate.
Compiles clean, but no ritual has been run on a device. The natives are in the APK
as of the previous commit; the first real ritual is the actual test.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
c9b6bd7992