feat(kos): domain-separate instances with a per-instance salt - #446
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AdamDawidKrol wants to merge 1 commit into
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feat(kos): domain-separate instances with a per-instance salt#446AdamDawidKrol wants to merge 1 commit into
AdamDawidKrol wants to merge 1 commit into
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Add an `instance_id` to `kos::Sender`/`Receiver`, mixed into each base-OT-derived setup PRG seed via a tweakable correlation-robust hash (`FIXED_KEY_AES.tccr(instance_id, seed)`). KOS instances that share one global `delta` and the same base OT then derive independent extension transcripts, so per-instance leakage can no longer be composed to sample or recover `delta`. The mix is non-invertible in `seed`: a linear XOR mix 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.
AdamDawidKrol
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Jul 24, 2026
Addresses the review on this PR: each RCOT consumer gets its own KOS instance but they all share one global `delta`. Give each logical consumer a distinct `instance_id` (matched across prover and verifier: sender id N ↔ receiver id N; proxy uses a single fixed id) so the same-`delta` instances are domain-separated. Depends on the KOS `instance_id` change (ethereum/mpz#446). Until that lands in a release, the `[patch]` block temporarily points mpz at an alpha.6-compatible build of the same change.
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Adds an
instance_idtokos::Sender/Receiver, mixed into each base-OT-derived setup PRG seed via a tweakable correlation-robust hash:Prg::from_seed(FIXED_KEY_AES.tccr(instance_id, seed)).KOS's security is analysed for a single extension instance per
delta. When several instances share one globaldelta— as in tlsnotary/tlsn#1173, where each RCOT consumer gets its own instance — they fall outside that single-instance assumption, and the implementation does no per-instance domain separation.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. Single-instance callers can passBlock::ZERO.