mirror of
https://github.com/saymrwulf/swisspost-evoting-go-poc.git
synced 2026-07-24 19:43:51 +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>
56 lines
1.5 KiB
Go
56 lines
1.5 KiB
Go
package math
|
|
|
|
import (
|
|
"crypto/rand"
|
|
"math/big"
|
|
)
|
|
|
|
// RandomZqElement generates a uniform random element in Z_q = [0, q).
|
|
func RandomZqElement(group *ZqGroup) ZqElement {
|
|
r, err := rand.Int(rand.Reader, group.q)
|
|
if err != nil {
|
|
panic("crypto/rand failed: " + err.Error())
|
|
}
|
|
return ZqElement{value: r, group: group}
|
|
}
|
|
|
|
// RandomZqVector generates a vector of n random elements in Z_q.
|
|
func RandomZqVector(n int, group *ZqGroup) *ZqVector {
|
|
elements := make([]ZqElement, n)
|
|
for i := range elements {
|
|
elements[i] = RandomZqElement(group)
|
|
}
|
|
return &ZqVector{elements: elements, group: group}
|
|
}
|
|
|
|
// RandomGqElement generates a uniform random element in G_q by squaring a
|
|
// random square root drawn from the canonical half [1, q].
|
|
func RandomGqElement(group *GqGroup) GqElement {
|
|
// rand.Int yields [0, q); shift to the canonical root range [1, q].
|
|
r, err := rand.Int(rand.Reader, group.q)
|
|
if err != nil {
|
|
panic("crypto/rand failed: " + err.Error())
|
|
}
|
|
r.Add(r, big.NewInt(1))
|
|
squared := new(big.Int).Exp(r, big.NewInt(2), group.p)
|
|
return GqElement{value: squared, group: group}
|
|
}
|
|
|
|
// RandomBigInt generates a random big.Int in [0, max).
|
|
func RandomBigInt(max *big.Int) *big.Int {
|
|
r, err := rand.Int(rand.Reader, max)
|
|
if err != nil {
|
|
panic("crypto/rand failed: " + err.Error())
|
|
}
|
|
return r
|
|
}
|
|
|
|
// RandomNonZeroZqElement generates a random non-zero element in Z_q.
|
|
func RandomNonZeroZqElement(group *ZqGroup) ZqElement {
|
|
for {
|
|
e := RandomZqElement(group)
|
|
if !e.IsZero() {
|
|
return e
|
|
}
|
|
}
|
|
}
|