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zeekay
93c5705815
Closer (a) committed.go: cSHAKE256-committed BGW re-shares + exact degree check (CheckDegree). Hash commitment is full-range-safe; the vss lattice Pedersen binds only SHORT openings (MSIS) and is unsound for full-range GF(q) re-shares — documented load-bearing departure from the HANDOFF seam. Closer (c) openshare.go: commit-then-open binding names equivocators directly. Identification rests on commitment binding, NOT RS error-correction (unsound at N=2T-1 against T-1 corruptions — a T-1 coalition out-votes the honest T). Closer (b) bitcheck.go: batched b·(b-1)=0 proof, Fiat-Shamir challenge bound to the bit commitments, opened once (non-bit survives w.p. 1/q), per-party drill-down. blame_bridge.go: mpc->blame bridge (scalar analogue of vss/blame.go); blame/ gains ReasonBadReshare/BadOpening/BadBit + evidence shapes. Each re-check binds the accused via its own signature, re-runs the scalar math — third-party verifiable. go build/test/-race/vet green.
32 lines
1.3 KiB
Go
32 lines
1.3 KiB
Go
// Copyright (C) 2025-2026, Lux Industries Inc. All rights reserved.
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// See the file LICENSE for licensing terms.
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package mpc
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import "golang.org/x/crypto/sha3"
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// stream.go — a domain-separated cSHAKE256 byte stream. Used to (1) expand a
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// Fiat-Shamir transcript hash into field elements (the bit-check challenge), and
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// (2) give each independent CSCP coefficient its own reproducible, race-free
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// randomness source derived from one master seed. It is an io.Reader so the
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// field samplers (Field.Rand, RandBit) drive it directly.
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// CShakeReader is an unbounded cSHAKE256 output stream keyed by a function name,
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// a customization domain, and a seed. Reproducible: the same (funcName,
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// customization, seed) yields the same bytes, so a committee run is KAT-stable
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// and parallel workers never share state.
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type CShakeReader struct {
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h sha3.ShakeHash
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}
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// NewCShakeReader builds a cSHAKE256 stream over (funcName, customization, seed).
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func NewCShakeReader(funcName, customization string, seed []byte) *CShakeReader {
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h := sha3.NewCShake256([]byte(funcName), []byte(customization))
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_, _ = h.Write(seed)
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return &CShakeReader{h: h}
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}
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// Read fills p with stream bytes; it never returns an error (cSHAKE is
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// unbounded).
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func (r *CShakeReader) Read(p []byte) (int, error) { return r.h.Read(p) }
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