mirror of
https://github.com/saymrwulf/swisspost-evoting-go-poc.git
synced 2026-05-14 20:58:03 +00:00
saymrwulf
e8b6f30871
Proof-of-concept reimplementation of the Swiss Post e-voting cryptographic protocol in Go. Single binary, 52 source files, 2 dependencies. Covers ElGamal encryption, Bayer-Groth verifiable shuffles, zero-knowledge proofs, return codes, and a full election ceremony demo.
71 lines
1.5 KiB
Go
71 lines
1.5 KiB
Go
package mixnet
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import (
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"math/big"
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emath "github.com/user/evote/pkg/math"
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)
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// Permutation represents a random permutation of [0, N).
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type Permutation struct {
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table []int
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}
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// GenPermutation generates a random permutation of size N using Fisher-Yates.
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func GenPermutation(n int) Permutation {
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table := make([]int, n)
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for i := range table {
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table[i] = i
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}
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for i := 0; i < n; i++ {
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// offset = random integer in [0, n-i)
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max := big.NewInt(int64(n - i))
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offset := emath.RandomBigInt(max).Int64()
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// Swap table[i] with table[i+offset]
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j := i + int(offset)
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table[i], table[j] = table[j], table[i]
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}
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return Permutation{table: table}
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}
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// Apply returns π[i].
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func (p Permutation) Apply(i int) int {
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return p.table[i]
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}
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// Size returns N.
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func (p Permutation) Size() int {
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return len(p.table)
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}
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// Table returns a copy of the permutation table.
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func (p Permutation) Table() []int {
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t := make([]int, len(p.table))
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copy(t, p.table)
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return t
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}
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// GetMatrixDimensions computes size-optimal m×n dimensions for a vector of size N.
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// Returns (m, n) where m <= n, m*n = N, and m is the largest factor ≤ √N.
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func GetMatrixDimensions(vectorSize int) (int, int) {
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if vectorSize < 2 {
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panic("size must be >= 2")
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}
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m := 1
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n := vectorSize
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sqrtN := isqrt(vectorSize)
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for i := sqrtN; i > 1; i-- {
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if vectorSize%i == 0 {
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m = i
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n = vectorSize / i
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break
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}
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}
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return m, n
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}
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func isqrt(n int) int {
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x := int64(n)
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s := new(big.Int).Sqrt(big.NewInt(x))
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return int(s.Int64())
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}
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