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x3dh.go
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x3dh.go
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package encryption
import (
"crypto/ecdsa"
"errors"
"sort"
"strconv"
"time"
"github.com/status-im/status-go/eth-node/crypto"
"github.com/status-im/status-go/eth-node/crypto/ecies"
)
const (
// Shared secret key length
sskLen = 16
)
func buildSignatureMaterial(bundle *Bundle) []byte {
signedPreKeys := bundle.GetSignedPreKeys()
timestamp := bundle.GetTimestamp()
var keys []string
for k := range signedPreKeys {
keys = append(keys, k)
}
var signatureMaterial []byte
sort.Strings(keys)
for _, installationID := range keys {
signedPreKey := signedPreKeys[installationID]
signatureMaterial = append(signatureMaterial, []byte(installationID)...)
signatureMaterial = append(signatureMaterial, signedPreKey.SignedPreKey...)
signatureMaterial = append(signatureMaterial, []byte(strconv.FormatUint(uint64(signedPreKey.Version), 10))...)
// We don't use timestamp in the signature if it's 0, for backward compatibility
}
if timestamp != 0 {
signatureMaterial = append(signatureMaterial, []byte(strconv.FormatInt(timestamp, 10))...)
}
return signatureMaterial
}
// SignBundle signs the bundle and refreshes the timestamps
func SignBundle(identity *ecdsa.PrivateKey, bundleContainer *BundleContainer) error {
bundleContainer.Bundle.Timestamp = time.Now().UnixNano()
signatureMaterial := buildSignatureMaterial(bundleContainer.GetBundle())
signature, err := crypto.Sign(crypto.Keccak256(signatureMaterial), identity)
if err != nil {
return err
}
bundleContainer.Bundle.Signature = signature
return nil
}
// NewBundleContainer creates a new BundleContainer from an identity private key
func NewBundleContainer(identity *ecdsa.PrivateKey, installationID string) (*BundleContainer, error) {
preKey, err := crypto.GenerateKey()
if err != nil {
return nil, err
}
compressedPreKey := crypto.CompressPubkey(&preKey.PublicKey)
compressedIdentityKey := crypto.CompressPubkey(&identity.PublicKey)
encodedPreKey := crypto.FromECDSA(preKey)
signedPreKeys := make(map[string]*SignedPreKey)
signedPreKeys[installationID] = &SignedPreKey{
ProtocolVersion: protocolVersion,
SignedPreKey: compressedPreKey,
}
bundle := Bundle{
Timestamp: time.Now().UnixNano(),
Identity: compressedIdentityKey,
SignedPreKeys: signedPreKeys,
}
return &BundleContainer{
Bundle: &bundle,
PrivateSignedPreKey: encodedPreKey,
}, nil
}
// VerifyBundle checks that a bundle is valid
func VerifyBundle(bundle *Bundle) error {
_, err := ExtractIdentity(bundle)
return err
}
// ExtractIdentity extracts the identity key from a given bundle
func ExtractIdentity(bundle *Bundle) (*ecdsa.PublicKey, error) {
bundleIdentityKey, err := crypto.DecompressPubkey(bundle.GetIdentity())
if err != nil {
return nil, err
}
signatureMaterial := buildSignatureMaterial(bundle)
recoveredKey, err := crypto.SigToPub(
crypto.Keccak256(signatureMaterial),
bundle.GetSignature(),
)
if err != nil {
return nil, err
}
if crypto.PubkeyToAddress(*recoveredKey) != crypto.PubkeyToAddress(*bundleIdentityKey) {
return nil, errors.New("identity key and signature mismatch")
}
return recoveredKey, nil
}
// PerformDH generates a shared key given a private and a public key
func PerformDH(privateKey *ecies.PrivateKey, publicKey *ecies.PublicKey) ([]byte, error) {
return privateKey.GenerateShared(
publicKey,
sskLen,
sskLen,
)
}
func getSharedSecret(dh1 []byte, dh2 []byte, dh3 []byte) []byte {
secretInput := append(append(dh1, dh2...), dh3...)
return crypto.Keccak256(secretInput)
}
// x3dhActive handles initiating an X3DH session
func x3dhActive(
myIdentityKey *ecies.PrivateKey,
theirSignedPreKey *ecies.PublicKey,
myEphemeralKey *ecies.PrivateKey,
theirIdentityKey *ecies.PublicKey,
) ([]byte, error) {
var dh1, dh2, dh3 []byte
var err error
if dh1, err = PerformDH(myIdentityKey, theirSignedPreKey); err != nil {
return nil, err
}
if dh2, err = PerformDH(myEphemeralKey, theirIdentityKey); err != nil {
return nil, err
}
if dh3, err = PerformDH(myEphemeralKey, theirSignedPreKey); err != nil {
return nil, err
}
return getSharedSecret(dh1, dh2, dh3), nil
}
// x3dhPassive handles the response to an initiated X3DH session
func x3dhPassive(
theirIdentityKey *ecies.PublicKey,
mySignedPreKey *ecies.PrivateKey,
theirEphemeralKey *ecies.PublicKey,
myIdentityKey *ecies.PrivateKey,
) ([]byte, error) {
var dh1, dh2, dh3 []byte
var err error
if dh1, err = PerformDH(mySignedPreKey, theirIdentityKey); err != nil {
return nil, err
}
if dh2, err = PerformDH(myIdentityKey, theirEphemeralKey); err != nil {
return nil, err
}
if dh3, err = PerformDH(mySignedPreKey, theirEphemeralKey); err != nil {
return nil, err
}
return getSharedSecret(dh1, dh2, dh3), nil
}
// PerformActiveDH performs a Diffie-Hellman exchange using a public key and a generated ephemeral key.
// Returns the key resulting from the DH exchange as well as the ephemeral public key.
func PerformActiveDH(publicKey *ecdsa.PublicKey) ([]byte, *ecdsa.PublicKey, error) {
ephemeralKey, err := crypto.GenerateKey()
if err != nil {
return nil, nil, err
}
key, err := PerformDH(
ecies.ImportECDSA(ephemeralKey),
ecies.ImportECDSAPublic(publicKey),
)
if err != nil {
return nil, nil, err
}
return key, &ephemeralKey.PublicKey, err
}
// PerformActiveX3DH takes someone else's bundle and calculates shared secret.
// Returns the shared secret and the ephemeral key used.
func PerformActiveX3DH(identity []byte, signedPreKey []byte, prv *ecdsa.PrivateKey) ([]byte, *ecdsa.PublicKey, error) {
bundleIdentityKey, err := crypto.DecompressPubkey(identity)
if err != nil {
return nil, nil, err
}
bundleSignedPreKey, err := crypto.DecompressPubkey(signedPreKey)
if err != nil {
return nil, nil, err
}
ephemeralKey, err := crypto.GenerateKey()
if err != nil {
return nil, nil, err
}
sharedSecret, err := x3dhActive(
ecies.ImportECDSA(prv),
ecies.ImportECDSAPublic(bundleSignedPreKey),
ecies.ImportECDSA(ephemeralKey),
ecies.ImportECDSAPublic(bundleIdentityKey),
)
if err != nil {
return nil, nil, err
}
return sharedSecret, &ephemeralKey.PublicKey, nil
}
// PerformPassiveX3DH handles the part of the protocol where
// our interlocutor used our bundle, with ID of the signedPreKey,
// we loaded our identity key and the correct signedPreKey and we perform X3DH
func PerformPassiveX3DH(theirIdentityKey *ecdsa.PublicKey, mySignedPreKey *ecdsa.PrivateKey, theirEphemeralKey *ecdsa.PublicKey, myPrivateKey *ecdsa.PrivateKey) ([]byte, error) {
sharedSecret, err := x3dhPassive(
ecies.ImportECDSAPublic(theirIdentityKey),
ecies.ImportECDSA(mySignedPreKey),
ecies.ImportECDSAPublic(theirEphemeralKey),
ecies.ImportECDSA(myPrivateKey),
)
if err != nil {
return nil, err
}
return sharedSecret, nil
}