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zkidentity.go
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zkidentity.go
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// Copyright (c) 2016 Company 0, LLC.
// Use of this source code is governed by an ISC
// license that can be found in the LICENSE file.
// zkidentity package manages public and private identities.
package zkidentity
import (
"bytes"
"crypto/rand"
"crypto/sha256"
"encoding/hex"
"errors"
"fmt"
"github.com/companyzero/sntrup4591761"
xdr "github.com/davecgh/go-xdr/xdr2"
"golang.org/x/crypto/ed25519"
)
var (
prng = rand.Reader
ErrNotEqual = errors.New("not equal")
ErrVerify = errors.New("verify error")
)
const (
IdentitySize = sha256.Size
)
// A zkc public identity consists of a name and nick (e.g "John Doe" and "jd"
// respectively), a ed25519 public signature key, and a NTRU Prime public key
// (used to derive symmetric encryption keys). An extra Identity field, taken
// as the SHA256 of the NTRU public key, is used as a short handle to uniquely
// identify a user in various zkc structures.
type PublicIdentity struct {
Name string
Nick string
SigKey [ed25519.PublicKeySize]byte
Key [sntrup4591761.PublicKeySize]byte
Identity [sha256.Size]byte
Digest [sha256.Size]byte // digest of name, keys and identity
Signature [ed25519.SignatureSize]byte // signature of Digest
}
type FullIdentity struct {
Public PublicIdentity
PrivateSigKey [ed25519.PrivateKeySize]byte
PrivateKey [sntrup4591761.PrivateKeySize]byte
}
func (fi *FullIdentity) Marshal() ([]byte, error) {
b := &bytes.Buffer{}
_, err := xdr.Marshal(b, fi)
if err != nil {
return nil, err
}
return b.Bytes(), nil
}
func UnmarshalFullIdentity(data []byte) (*FullIdentity, error) {
br := bytes.NewReader(data)
fi := FullIdentity{}
_, err := xdr.Unmarshal(br, &fi)
if err != nil {
return nil, err
}
return &fi, nil
}
func New(name, nick string) (*FullIdentity, error) {
ed25519Pub, ed25519Priv, err := ed25519.GenerateKey(prng)
if err != nil {
return nil, err
}
ntruprimePub, ntruprimePriv, err := sntrup4591761.GenerateKey(prng)
if err != nil {
return nil, err
}
identity := sha256.Sum256(ntruprimePub[:])
fi := new(FullIdentity)
fi.Public.Name = name
fi.Public.Nick = nick
copy(fi.Public.SigKey[:], ed25519Pub[:])
copy(fi.Public.Key[:], ntruprimePub[:])
copy(fi.Public.Identity[:], identity[:])
copy(fi.PrivateSigKey[:], ed25519Priv[:])
copy(fi.PrivateKey[:], ntruprimePriv[:])
err = fi.RecalculateDigest()
if err != nil {
return nil, err
}
zero(ed25519Pub[:])
zero(ed25519Priv[:])
zero(ntruprimePub[:])
zero(ntruprimePriv[:])
return fi, nil
}
func Fingerprint(id [IdentitySize]byte) string {
return hex.EncodeToString(id[:])
}
func (fi *FullIdentity) RecalculateDigest() error {
// calculate digest
d := sha256.New()
d.Write([]byte(fi.Public.Name))
d.Write([]byte(fi.Public.Nick))
d.Write(fi.Public.SigKey[:])
d.Write(fi.Public.Key[:])
d.Write(fi.Public.Identity[:])
copy(fi.Public.Digest[:], d.Sum(nil))
// sign and verify
signature := ed25519.Sign(fi.PrivateSigKey[:], fi.Public.Digest[:])
copy(fi.Public.Signature[:], signature)
if !fi.Public.Verify() {
return fmt.Errorf("could not verify public signature")
}
return nil
}
func (fi *FullIdentity) SignMessage(message []byte) [ed25519.SignatureSize]byte {
var sig [ed25519.SignatureSize]byte
copy(sig[:], ed25519.Sign(fi.PrivateSigKey[:], message))
return sig
}
func (p PublicIdentity) VerifyMessage(msg []byte, sig [ed25519.SignatureSize]byte) bool {
return ed25519.Verify(p.SigKey[:], msg, sig[:])
}
func (p PublicIdentity) String() string {
return hex.EncodeToString(p.Identity[:])
}
func (p PublicIdentity) Fingerprint() string {
return Fingerprint(p.Identity)
}
func (p *PublicIdentity) Verify() bool {
d := sha256.New()
d.Write([]byte(p.Name))
d.Write([]byte(p.Nick))
d.Write(p.SigKey[:])
d.Write(p.Key[:])
d.Write(p.Identity[:])
if !bytes.Equal(p.Digest[:], d.Sum(nil)) {
return false
}
return ed25519.Verify(p.SigKey[:], p.Digest[:], p.Signature[:])
}
func (p *PublicIdentity) Marshal() ([]byte, error) {
b := &bytes.Buffer{}
_, err := xdr.Marshal(b, p)
if err != nil {
return nil, err
}
return b.Bytes(), nil
}
func UnmarshalPublicIdentity(data []byte) (*PublicIdentity, error) {
br := bytes.NewReader(data)
pi := PublicIdentity{}
_, err := xdr.Unmarshal(br, &pi)
if err != nil {
return nil, err
}
if !pi.Verify() {
return nil, ErrVerify
}
return &pi, nil
}
// Zero out a byte slice.
func zero(in []byte) {
if in == nil {
return
}
for i := 0; i < len(in); i++ {
in[i] ^= in[i]
}
}
func String2ID(to string) (*[32]byte, error) {
id, err := hex.DecodeString(to)
if err != nil {
return nil, err
}
if len(id) != 32 {
return nil, fmt.Errorf("invalid length")
}
var id32 [32]byte
copy(id32[:], id)
return &id32, nil
}