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.
63 lines
1.8 KiB
Go
63 lines
1.8 KiB
Go
package kdf
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import (
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"crypto/sha256"
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"io"
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"math/big"
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"golang.org/x/crypto/argon2"
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"golang.org/x/crypto/hkdf"
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emath "github.com/user/evote/pkg/math"
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)
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// DeriveKey derives a key using HKDF-SHA256.
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func DeriveKey(prk, info []byte, length int) []byte {
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reader := hkdf.Expand(sha256.New, prk, info)
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key := make([]byte, length)
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_, err := io.ReadFull(reader, key)
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if err != nil {
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panic("HKDF expand failed: " + err.Error())
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}
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return key
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}
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// KDFToZq derives a Z_q element using HKDF-SHA256.
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// PRK is the pseudorandom key, info is the context info, q is the modulus.
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func KDFToZq(prk []byte, info []byte, q *big.Int) *big.Int {
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// Derive enough bytes: ceil(q.BitLen() / 8) + extra for uniformity
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byteLen := (q.BitLen()+7)/8 + 16 // extra 16 bytes for rejection sampling avoidance
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derived := DeriveKey(prk, info, byteLen)
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val := new(big.Int).SetBytes(derived)
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return val.Mod(val, q)
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}
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// KDFToZqElement derives a ZqElement using HKDF-SHA256.
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func KDFToZqElement(prk []byte, info []byte, group *emath.ZqGroup) emath.ZqElement {
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val := KDFToZq(prk, info, group.Q())
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e, err := emath.NewZqElement(val, group)
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if err != nil {
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panic("KDFToZqElement: " + err.Error())
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}
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return e
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}
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// BuildKDFInfo builds a KDF info string from label and context parts.
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func BuildKDFInfo(parts ...string) []byte {
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var info []byte
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for _, p := range parts {
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info = append(info, []byte(p)...)
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}
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return info
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}
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// Argon2id derives a key using Argon2id.
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func Argon2id(password, salt []byte, time, memory uint32, threads uint8, keyLen uint32) []byte {
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return argon2.IDKey(password, salt, time, memory, threads, keyLen)
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}
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// DefaultArgon2id uses the default parameters from the Swiss Post e-voting system.
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func DefaultArgon2id(password, salt []byte) []byte {
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// Typical parameters from the protocol
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return Argon2id(password, salt, 3, 64*1024, 4, 32)
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}
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