mirror of
https://github.com/saymrwulf/swisspost-evoting-go-poc.git
synced 2026-09-04 20:23:55 +00:00
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>
66 lines
1.8 KiB
Go
66 lines
1.8 KiB
Go
package elgamal
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import (
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"math/big"
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"testing"
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emath "github.com/user/evote/pkg/math"
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)
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const (
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testP = "179688417486862032111147025351064878713905624387098436271724698527496946737299"
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testQ = "89844208743431016055573512675532439356952812193549218135862349263748473368649"
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testG = "4"
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)
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func testGroup(t *testing.T) *emath.GqGroup {
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t.Helper()
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p, _ := new(big.Int).SetString(testP, 10)
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q, _ := new(big.Int).SetString(testQ, 10)
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g, _ := new(big.Int).SetString(testG, 10)
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group, err := emath.NewGqGroup(p, q, g)
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if err != nil {
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t.Fatalf("test group: %v", err)
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}
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return group
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}
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func TestEncryptDecryptRoundTrip(t *testing.T) {
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group := testGroup(t)
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zq := emath.ZqGroupFromGqGroup(group)
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kp := GenKeyPair(group, 3)
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plain := NewMessage(emath.GqVectorOf(
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emath.RandomGqElement(group),
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emath.RandomGqElement(group),
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emath.RandomGqElement(group),
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))
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ct := Encrypt(plain, emath.RandomZqElement(zq), kp.PK)
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got := Decrypt(ct, kp.SK)
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for i := 0; i < plain.Size(); i++ {
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if !got.Get(i).Equals(plain.Get(i)) {
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t.Fatalf("round-trip mismatch at %d", i)
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}
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}
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}
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// TestHomomorphicMultiplication checks Enc(m1)*Enc(m2) decrypts to m1*m2 —
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// the property the mix-net and return-code computations rely on.
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func TestHomomorphicMultiplication(t *testing.T) {
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group := testGroup(t)
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zq := emath.ZqGroupFromGqGroup(group)
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kp := GenKeyPair(group, 1)
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m1 := emath.RandomGqElement(group)
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m2 := emath.RandomGqElement(group)
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ct1 := Encrypt(NewMessage(emath.GqVectorOf(m1)), emath.RandomZqElement(zq), kp.PK)
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ct2 := Encrypt(NewMessage(emath.GqVectorOf(m2)), emath.RandomZqElement(zq), kp.PK)
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product := ct1.Multiply(ct2)
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got := Decrypt(product, kp.SK).Get(0)
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want := m1.Multiply(m2)
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if !got.Equals(want) {
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t.Fatal("homomorphic product decrypts incorrectly")
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}
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}
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