feat(kos): domain-separate instances with a per-instance salt - #2
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Each RCOT consumer now gets its own KOS instance (deadlock fix), but they all reuse one global delta. Give each logical consumer a distinct `instance_id` salt so the instances are domain-separated, closing the shared-delta leak flagged in review of tlsnotary/tlsn#1173. Ids are assigned explicitly per consumer so prover and verifier stay matched (sender id N pairs with receiver id N); proxy mode uses a single fixed id. Depends on the mpz salt (AdamDawidKrol/mpz#2), pulled via the [patch] block.
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Each RCOT consumer now gets its own KOS instance (deadlock fix), but they all reuse one global delta. Give each logical consumer a distinct `instance_id` salt so the instances are domain-separated, closing the shared-delta leak flagged in review of tlsnotary/tlsn#1173. Ids are assigned explicitly per consumer so prover and verifier stay matched (sender id N pairs with receiver id N); proxy mode uses a single fixed id. Depends on the mpz salt (AdamDawidKrol/mpz#2), pulled via the [patch] block.
Add an `instance_id` salt to `kos::Sender`/`Receiver`, mixed into the base-OT-derived setup PRG seeds via a tweakable correlation-robust hash (`FIXED_KEY_AES.tccr(instance_id, seed)`). Two KOS instances that share one global `delta` and the same base OT then produce independent extension transcripts, so per-instance consistency-check leakage can no longer be composed to sample or recover `delta` (demonstrated in #1). The mix is non-invertible in `seed` on purpose: a linear XOR mix (`seed ^ instance_id`) would let a malicious receiver, who controls the base-OT seeds, pre-compensate them to cancel the salt and collapse two instances onto one PRG stream. API-breaking: `Sender::new`/`Receiver::new` gain an `instance_id: Block`. Paired sender and receiver must use the same id; distinct instances reusing one `delta` must use distinct ids.
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Each RCOT consumer now gets its own KOS instance (deadlock fix), but they all reuse one global delta. Give each logical consumer a distinct `instance_id` salt so the instances are domain-separated, closing the shared-delta leak flagged in review of tlsnotary/tlsn#1173. Ids are assigned explicitly per consumer so prover and verifier stay matched (sender id N pairs with receiver id N); proxy mode uses a single fixed id. Depends on the mpz salt (AdamDawidKrol/mpz#2), pulled via the [patch] block.
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Adds an
instance_idsalt tokos::Sender/Receiver, mixed into the base-OT-derived setup PRG seeds via a tweakable correlation-robust hash:Prg::from_seed(FIXED_KEY_AES.tccr(instance_id, seed)).Two KOS instances that share one global
deltaand the same base OT then produce independent extension transcripts, so per-instance consistency-check leakage can no longer be composed to sample/recoverdelta(the issue raised in review of tlsnotary/tlsn#1173).API-breaking:
Sender::new/Receiver::newgain aninstance_id: Block. Paired sender and receiver must use the same id; distinct instances reusing onedeltamust use distinct ids.Consumed by AdamDawidKrol/tlsn#2.