package rsa
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import (
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"bytes"
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"crypto/rand"
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"math/big"
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)
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const (
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bits = 512 // 2048
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)
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var bigOne = big.NewInt(int64(1))
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type PublicKey struct {
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E *big.Int `json:"e"`
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N *big.Int `json:"n"`
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}
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type PublicKeyString struct {
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E string `json:"e"`
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N string `json:"n"`
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}
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type PrivateKey struct {
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D *big.Int `json:"d"`
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N *big.Int `json:"n"`
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}
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type Key struct {
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PubK PublicKey
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PrivK PrivateKey
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}
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func GenerateKeyPair() (key Key, err error) {
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p, err := rand.Prime(rand.Reader, bits/2)
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if err != nil {
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return key, err
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}
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q, err := rand.Prime(rand.Reader, bits/2)
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if err != nil {
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return key, err
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}
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n := new(big.Int).Mul(p, q)
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p_1 := new(big.Int).Sub(p, bigOne)
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q_1 := new(big.Int).Sub(q, bigOne)
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phi := new(big.Int).Mul(p_1, q_1)
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e := 65537
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var pubK PublicKey
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pubK.E = big.NewInt(int64(e))
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pubK.N = n
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d := new(big.Int).ModInverse(big.NewInt(int64(e)), phi)
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var privK PrivateKey
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privK.D = d
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privK.N = n
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key.PubK = pubK
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key.PrivK = privK
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return key, nil
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}
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func Encrypt(m *big.Int, pubK PublicKey) *big.Int {
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c := new(big.Int).Exp(m, pubK.E, pubK.N)
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return c
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}
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func Decrypt(c *big.Int, privK PrivateKey) *big.Int {
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m := new(big.Int).Exp(c, privK.D, privK.N)
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return m
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}
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func Blind(m *big.Int, r *big.Int, pubK PublicKey) *big.Int {
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rE := new(big.Int).Exp(r, pubK.E, nil)
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mrE := new(big.Int).Mul(m, rE)
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mBlinded := new(big.Int).Mod(mrE, pubK.N)
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return mBlinded
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}
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func BlindSign(m *big.Int, privK PrivateKey) *big.Int {
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sigma := new(big.Int).Exp(m, privK.D, privK.N)
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return sigma
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}
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func Unblind(sigma *big.Int, r *big.Int, pubK PublicKey) *big.Int {
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r1 := new(big.Int).ModInverse(r, pubK.N)
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bsr := new(big.Int).Mul(sigma, r1)
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sig := new(big.Int).Mod(bsr, pubK.N)
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return sig
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}
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func Verify(msg *big.Int, mSigned *big.Int, pubK PublicKey) bool {
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//decrypt the mSigned with pubK
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Cd := new(big.Int).Exp(mSigned, pubK.E, nil)
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m := new(big.Int).Mod(Cd, pubK.N)
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return bytes.Equal(msg.Bytes(), m.Bytes())
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}
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func HomomorphicMul(c1 *big.Int, c2 *big.Int, pubK PublicKey) *big.Int {
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c1c2 := new(big.Int).Mul(c1, c2)
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n2 := new(big.Int).Mul(pubK.N, pubK.N)
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d := new(big.Int).Mod(c1c2, n2)
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return d
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}
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