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https://github.com/saymrwulf/swisspost-evoting-go-poc.git
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saymrwulf
ec4be74e17
Correctness/security review of the whole PoC, with fixes and regression tests.
Cryptographic soundness:
- mixnet: enforce the multi-exponentiation c_{B_m}=commit(0;0) check that was
stubbed out with an empty if — without it a malicious mixer can prove a
non-permutation shuffle.
- zkp: derive all four Fiat-Shamir challenges via RecursiveHashToZq instead of
a biased `hash mod q` (which also capped the challenge space at 256 bits for
production-sized groups).
Verification honesty:
- protocol: VerifyTally now actually calls zkp.VerifySchnorrProof and returns
the true aggregate result instead of an unconditional true.
- protocol: persist the padded mix input (event.MixInput) so the verifier checks
shuffle 0 against the same padding the tally used (fixes false INVALID for N<2).
Other correctness:
- kdf: length-prefix BuildKDFInfo parts so the info encoding is injective.
- math: GqElementFromSquareRoot accepts the valid root q (off-by-one that could
panic in HashAndSquare); RandomGqElement samples the full canonical range.
- cmd: validate demo --voters/--options instead of panicking on degenerate values.
- protocol: use crypto/rand in the demo driver (drop the last math/rand import).
Transport security (new): pkg/transportsec exposes Ed25519 signatures and X25519
ECDH — implemented in Rust (rust/transportsec: ed25519-dalek, x25519-dalek),
linked into Go via cgo. No RSA. Cross-language conformance test proves the Rust
Ed25519 signatures interoperate with Go's crypto/ed25519. Makefile builds the
Rust static lib before the Go binary.
Tests: added unit/round-trip/tamper coverage for math, hash, elgamal, zkp,
mixnet, kdf, returncodes, protocol (end-to-end), and the Rust FFI bridge.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
25 lines
777 B
Go
25 lines
777 B
Go
package kdf
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import (
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"bytes"
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"testing"
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)
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// TestBuildKDFInfoInjective locks in the domain-separation fix: part tuples
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// that would concatenate to the same bytes must now produce distinct info
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// strings (e.g. ("e1","23x") vs ("e12","3x")).
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func TestBuildKDFInfoInjective(t *testing.T) {
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a := BuildKDFInfo("e1", "23x")
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b := BuildKDFInfo("e12", "3x")
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if bytes.Equal(a, b) {
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t.Fatal("distinct part tuples collided into the same KDF info")
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}
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// Same parts must be deterministic.
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if !bytes.Equal(BuildKDFInfo("label", "ctx"), BuildKDFInfo("label", "ctx")) {
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t.Fatal("BuildKDFInfo is not deterministic")
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}
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// A boundary vs. joined variant must differ too.
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if bytes.Equal(BuildKDFInfo("a", "bc"), BuildKDFInfo("ab", "c")) {
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t.Fatal("boundary shift collided")
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}
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}
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