mirror of
https://github.com/saymrwulf/swisspost-evoting-go-poc.git
synced 2026-07-24 19:43:51 +00:00
saymrwulf
23723fddd6
The mix-net now runs across separate parties over the signed transport: the server pads the ballot box and hands it to CC0; each CC shuffles + partially decrypts and passes the (validated) ciphertexts to the next; the electoral board performs the final shuffle + decryption. Ciphertext handoffs cross the authenticated transport; each party posts its shuffle and decryption proofs to the public transcript (the bulletin board). - tally.go: RunTally orchestration + per-party handlers (server pad, CC shuffle, EB final decrypt). Persists the padded mix input and per-stage partial decrypts to the transcript (fixes F7/F8 in the multi-party setting). - verify.go: RunVerify has the verifier independently re-check every CC Schnorr proof and the whole shuffle chain from the transcript alone (no secrets). - returncodes: DecodeVoteChecked returns an error instead of panicking on a non-smooth plaintext (fixes F12), used on the tally path so a corrupt ballot is counted as spoiled rather than crashing the tally. Tests: the full ceremony (setup -> cards -> voting -> tally -> verify) produces the correct tally over 124 verified transport messages; the verifier rejects a transcript with swapped Schnorr proofs. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
42 lines
1.2 KiB
Go
42 lines
1.2 KiB
Go
package returncodes
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import (
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"fmt"
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"math/big"
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)
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// DecodeVote factorizes a vote product back into the indices of selected
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// options. It panics if the product is not a smooth product of the encoding
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// primes; use DecodeVoteChecked when the input may be untrusted.
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func DecodeVote(product *big.Int, primes []*big.Int) []int {
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selected, err := DecodeVoteChecked(product, primes)
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if err != nil {
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panic(err.Error())
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}
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return selected
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}
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// DecodeVoteChecked is like DecodeVote but returns an error instead of panicking
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// when the product does not fully factor over the encoding primes (which can
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// happen for a corrupted or malicious ciphertext once inputs are remote).
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func DecodeVoteChecked(product *big.Int, primes []*big.Int) ([]int, error) {
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remaining := new(big.Int).Set(product)
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var selected []int
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for idx, p := range primes {
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for {
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quo, rem := new(big.Int).DivMod(remaining, p, new(big.Int))
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if rem.Sign() == 0 {
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selected = append(selected, idx)
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remaining = quo
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} else {
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break
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}
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}
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}
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if remaining.Cmp(big.NewInt(1)) != 0 {
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return nil, fmt.Errorf("vote does not factor over encoding primes (remaining %s)", remaining.String())
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}
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return selected, nil
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}
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