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server.go
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server.go
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/*
* Copyright (C) 2015-2018 Virgil Security Inc.
*
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are
* met:
*
* (1) Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
*
* (2) Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in
* the documentation and/or other materials provided with the
* distribution.
*
* (3) Neither the name of the copyright holder nor the names of its
* contributors may be used to endorse or promote products derived from
* this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE AUTHOR ''AS IS'' AND ANY EXPRESS OR
* IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
* WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
* DISCLAIMED. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT,
* INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
* (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
* SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
* STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING
* IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
* POSSIBILITY OF SUCH DAMAGE.
*
* Lead Maintainer: Virgil Security Inc. <support@virgilsecurity.com>
*/
package phe
import (
"crypto/rand"
"github.com/pkg/errors"
)
// GenerateServerKeypair creates a new random Nist p-256 keypair
func GenerateServerKeypair() ([]byte, error) {
privateKey := randomZ().Bytes()
publicKey := new(Point).ScalarBaseMult(privateKey)
return marshalKeypair(publicKey.Marshal(), privateKey)
}
// GetEnrollment generates a new random enrollment record and a proof
func GetEnrollment(serverKeypair []byte) (*EnrollmentResponse, error) {
kp, err := unmarshalKeypair(serverKeypair)
if err != nil {
return nil, err
}
ns := make([]byte, 32)
_, err = rand.Read(ns)
if err != nil {
return nil, err
}
hs0, hs1, c0, c1 := eval(kp, ns)
proof := proveSuccess(kp, hs0, hs1, c0, c1)
return &EnrollmentResponse{
NS: ns,
C0: c0.Marshal(),
C1: c1.Marshal(),
Proof: proof,
}, nil
}
// GetPublicKey returns server public key
func GetPublicKey(serverKeypair []byte) ([]byte, error) {
key, err := unmarshalKeypair(serverKeypair)
if err != nil {
return nil, err
}
return key.PublicKey, nil
}
// VerifyPassword compares password attempt to the one server would calculate itself using its private key
// and returns a zero knowledge proof of ether success or failure
func VerifyPassword(serverKeypair []byte, req *VerifyPasswordRequest) (response *VerifyPasswordResponse, err error) {
kp, err := unmarshalKeypair(serverKeypair)
if err != nil {
return nil, err
}
if req == nil || len(req.NS) > 32 || len(req.NS) == 0 {
err = errors.New("Invalid password verify request")
return
}
ns := req.NS
c0, err := PointUnmarshal(req.C0)
if err != nil {
return
}
hs0 := hashToPoint(dhs0, ns)
hs1 := hashToPoint(dhs1, ns)
if hs0.ScalarMult(kp.PrivateKey).Equal(c0) {
//password is ok
c1 := hs1.ScalarMult(kp.PrivateKey)
response = &VerifyPasswordResponse{
Res: true,
C1: c1.Marshal(),
ProofSuccess: proveSuccess(kp, hs0, hs1, c0, c1),
}
return
}
//password is invalid
c1, proof, err := proveFailure(kp, c0, hs0)
if err != nil {
return
}
response = &VerifyPasswordResponse{
Res: false,
C1: c1.Marshal(),
ProofFail: proof,
}
return
}
func eval(kp *keypair, ns []byte) (hs0, hs1, c0, c1 *Point) {
hs0 = hashToPoint(dhs0, ns)
hs1 = hashToPoint(dhs1, ns)
c0 = hs0.ScalarMult(kp.PrivateKey)
c1 = hs1.ScalarMult(kp.PrivateKey)
return
}
func proveSuccess(kp *keypair, hs0, hs1, c0, c1 *Point) *ProofOfSuccess {
blindX := randomZ()
term1 := hs0.ScalarMult(blindX.Bytes())
term2 := hs1.ScalarMult(blindX.Bytes())
term3 := new(Point).ScalarBaseMult(blindX.Bytes())
//challenge = group.hash((self.X, self.G, c0, c1, term1, term2, term3), target_type=ZR)
challenge := hashZ(proofOk, kp.PublicKey, curveG.Marshal(), c0.Marshal(), c1.Marshal(), term1.Marshal(), term2.Marshal(), term3.Marshal())
res := gf.Add(blindX, gf.MulBytes(kp.PrivateKey, challenge))
return &ProofOfSuccess{
Term1: term1.Marshal(),
Term2: term2.Marshal(),
Term3: term3.Marshal(),
BlindX: res.Bytes(),
}
}
func proveFailure(kp *keypair, c0, hs0 *Point) (c1 *Point, proof *ProofOfFail, err error) {
r := randomZ()
minusR := gf.Neg(r)
minusRX := gf.MulBytes(kp.PrivateKey, minusR)
c1 = c0.ScalarMult(r.Bytes()).Add(hs0.ScalarMult(minusRX.Bytes()))
a := r
b := minusRX
blindA := randomZ().Bytes()
blindB := randomZ().Bytes()
publicKey, err := PointUnmarshal(kp.PublicKey)
if err != nil {
return
}
// I = (self.X ** a) * (self.G ** b)
// term1 = c0 ** blind_a
// term2 = hs0 ** blind_b
// term3 = self.X ** blind_a
// term4 = self.G ** blind_b
term1 := c0.ScalarMult(blindA)
term2 := hs0.ScalarMult(blindB)
term3 := publicKey.ScalarMult(blindA)
term4 := new(Point).ScalarBaseMult(blindB)
challenge := hashZ(proofError, kp.PublicKey, curveG.Marshal(), c0.Marshal(), c1.Marshal(), term1.Marshal(), term2.Marshal(), term3.Marshal(), term4.Marshal())
return c1, &ProofOfFail{
Term1: term1.Marshal(),
Term2: term2.Marshal(),
Term3: term3.Marshal(),
Term4: term4.Marshal(),
BlindA: gf.AddBytes(blindA, gf.Mul(challenge, a)).Bytes(),
BlindB: gf.AddBytes(blindB, gf.Mul(challenge, b)).Bytes(),
}, nil
}
//Rotate updates server's private and public keys and issues an update token for use on client's side
func Rotate(serverKeypair []byte) (token *UpdateToken, newServerKeypair []byte, err error) {
kp, err := unmarshalKeypair(serverKeypair)
if err != nil {
return
}
a, b := randomZ(), randomZ()
newPrivate := gf.Add(gf.MulBytes(kp.PrivateKey, a), b).Bytes()
newPublic := new(Point).ScalarBaseMult(newPrivate)
newServerKeypair, err = marshalKeypair(newPublic.Marshal(), newPrivate)
if err != nil {
return
}
token = &UpdateToken{
A: a.Bytes(),
B: b.Bytes(),
}
return
}