init: v1.0.0

he/elgamal/elgamal.go

@@ -0,0 +1,114 @@
+package elgamal
+
+import (
+	"crypto/rand"
+	"errors"
+	"io"
+	"math/big"
+
+	"xdx.jelly/xgcl/grand"
+)
+
+var Reader = grand.Reader
+
+type Params struct {
+	isMont bool // Is Montgomery represent
+	p      *big.Int
+	q      *big.Int
+	g      *big.Int
+	pMont  *big.Int
+	qMont  *big.Int
+	gMont  *big.Int
+}
+
+func (p *Params) P() *big.Int {
+	return p.p
+}
+func (p *Params) Q() *big.Int {
+	return p.q
+}
+func (p *Params) G() *big.Int {
+	return p.g
+}
+
+type PublicKey struct {
+	y      big.Int
+	Params *Params
+}
+
+type PrivateKey struct {
+	x big.Int
+	PublicKey
+}
+type Cipher struct {
+	u big.Int
+	v big.Int
+}
+
+func GenerateKey(rnd io.Reader, params *Params) (*PrivateKey, *PublicKey, error) {
+	x, err := rand.Int(rnd, params.q)
+	if err != nil {
+		return nil, nil, err
+	}
+	y := new(big.Int).Exp(params.g, x, params.p)
+	sk := &PrivateKey{
+		x: *x,
+		PublicKey: PublicKey{
+			y:      *y,
+			Params: P1024,
+		},
+	}
+	pk := &sk.PublicKey
+	return sk, pk, nil
+}
+
+// m = g^M mod p for some M
+// rnd can be nil, io.Reader or []byte
+func (pk *PublicKey) Encryption(m *big.Int, rnd any) (*Cipher, error) {
+	var r *big.Int
+	var err error
+	p := pk.Params.p
+	q := pk.Params.q
+	g := pk.Params.g
+
+	switch rnd := rnd.(type) {
+	case nil:
+		rnd = Reader
+	case io.Reader:
+		r, err = rand.Int(rnd, q)
+		if err != nil {
+			return nil, err
+		}
+	case []byte:
+		r = new(big.Int).SetBytes(rnd)
+		if r.Cmp(q) >= 0 {
+			return nil, errors.New("random bytes too large")
+		}
+	default:
+		return nil, errors.New("rnd must be io.Reader or []bytes")
+	}
+
+	c := &Cipher{}
+	c.u.Exp(g, r, p)
+	c.v.Exp(&pk.y, r, p)
+	c.v.Mul(&c.v, m)
+	return c, nil
+}
+
+func (sk *PrivateKey) Decryption(c *Cipher) (*big.Int, error) {
+	p := sk.PublicKey.Params.p
+	u := &c.u
+	v := &c.v
+	z := new(big.Int)
+	z.Exp(u, &sk.x, p)
+	z.ModInverse(z, p)
+	z.Mul(z, v)
+	z.Mod(z, p)
+	return z, nil
+}
+
+func (c *Cipher) HomoMap(c1 *Cipher, c2 *Cipher) (*Cipher, error) {
+	c.u.Mul(&c1.u, &c2.u)
+	c.v.Mul(&c1.v, &c2.v)
+	return c, nil
+}