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Copy pathpair-passkey.go
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324 lines (303 loc) · 10.7 KB
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// Copyright (c) 2026 Tulir Asokan
//
// This Source Code Form is subject to the terms of the Mozilla Public
// License, v. 2.0. If a copy of the MPL was not distributed with this
// file, You can obtain one at http://mozilla.org/MPL/2.0/.
package whatsmeow
import (
"context"
"crypto/hmac"
"crypto/sha256"
"encoding/json"
"fmt"
"time"
"go.mau.fi/util/random"
"golang.org/x/crypto/curve25519"
"google.golang.org/protobuf/proto"
waBinary "go.mau.fi/whatsmeow/binary"
"go.mau.fi/whatsmeow/proto/waCompanionReg"
"go.mau.fi/whatsmeow/store"
"go.mau.fi/whatsmeow/types"
"go.mau.fi/whatsmeow/types/events"
"go.mau.fi/whatsmeow/util/gcmutil"
"go.mau.fi/whatsmeow/util/hkdfutil"
"go.mau.fi/whatsmeow/util/keys"
)
type passkeyLinkingCache struct {
keyPair *keys.KeyPair
companionNonce []byte
pairingRef string
deviceType waCompanionReg.DeviceProps_PlatformType
encryptionKey []byte
}
type passkeyHandoffKey struct {
hmac []byte
ts time.Time
}
func (k *passkeyHandoffKey) Valid() bool {
return k != nil && time.Since(k.ts) < 5*time.Minute
}
func (cli *Client) handlePasskeyNotification(ctx context.Context, node *waBinary.Node) {
if fromJID := node.AttrGetter().JID("from"); fromJID != types.ServerJID {
cli.Log.Warnf("Ignoring passkey notification from non-server JID %s", fromJID)
return
}
pubKey, err := parsePasskeyNotification(node)
if err != nil {
cli.Log.Warnf("Failed to parse passkey notification: %v", err)
var secondErr error
pubKey, secondErr = cli.getPasskeyRequestOptions(ctx)
if secondErr != nil {
cli.Log.Warnf("Failed to fetch passkey options: %v", secondErr)
cli.dispatchEvent(&events.PairPasskeyError{
Error: fmt.Errorf("failed to parse passkey notification: %w (fetching key also failed: %w)", err, secondErr),
Continuation: false,
})
return
}
cli.Log.Debugf("Successfully fetched passkey options after failing to parse notification")
}
cli.passkeyHandoffKey.Store(&passkeyHandoffKey{
hmac: hkdfutil.SHA256(cli.Store.AdvSecretKey, nil, []byte("shortcake-passkey-handoff-v1"), 32),
ts: time.Now(),
})
cli.Store.AdvSecretKey = random.Bytes(32)
cli.dispatchEvent(&events.PairPasskeyRequest{PublicKey: pubKey})
}
// SendPasskeyResponse sends a WebAuthn response from the authenticator to the server.
// This should be called after receiving an [*events.PairPasskeyRequest] and asking the authenticator for a response.
func (cli *Client) SendPasskeyResponse(ctx context.Context, passkeyResp *types.WebAuthnResponse) error {
marshaledResp, err := json.Marshal(passkeyResp)
if err != nil {
return fmt.Errorf("failed to marshal WebAuthnResponse: %w", err)
}
companionRef, err := cli.getCompanionRef(ctx)
if err != nil {
return fmt.Errorf("failed to get companion ref: %w", err)
}
companionEphemeralKeyPair := keys.NewKeyPair()
companionNonce := random.Bytes(32)
deviceType := store.DeviceProps.GetPlatformType()
ident, err := proto.Marshal(&waCompanionReg.CompanionEphemeralIdentity{
PublicKey: companionEphemeralKeyPair.Pub[:],
DeviceType: &deviceType,
Ref: &companionRef,
})
if err != nil {
return fmt.Errorf("failed to marshal CompanionEphemeralIdentity: %w", err)
}
commitment := sha256.Sum256(append(ident, companionNonce...))
prologuePayload, err := proto.Marshal(&waCompanionReg.ProloguePayload{
CompanionEphemeralIdentity: ident,
Commitment: &waCompanionReg.CompanionCommitment{
Hash: commitment[:],
},
})
if err != nil {
return fmt.Errorf("failed to marshal ProloguePayload: %w", err)
}
cli.passkeyLinkingCache.Store(&passkeyLinkingCache{
keyPair: companionEphemeralKeyPair,
companionNonce: companionNonce,
pairingRef: companionRef,
deviceType: deviceType,
})
prologueContent := []waBinary.Node{
{Tag: "credential_id", Content: []byte(passkeyResp.RawID)},
{Tag: "webauthn_assertion", Content: marshaledResp},
{Tag: "prologue_payload", Content: prologuePayload},
}
if handoffKey := cli.passkeyHandoffKey.Load(); handoffKey.Valid() {
h := hmac.New(sha256.New, handoffKey.hmac)
h.Write(prologuePayload)
pairingHandoffProof := h.Sum(nil)
prologueContent = append(prologueContent, waBinary.Node{
Tag: "pairing_handoff_proof",
Content: pairingHandoffProof,
})
cli.passkeySkipHandoffUX.Store(true)
} else {
cli.passkeySkipHandoffUX.Store(false)
}
_, err = cli.sendIQ(ctx, infoQuery{
Namespace: "md",
Type: iqSet,
To: types.ServerJID,
Content: []waBinary.Node{{
Tag: "passkey_prologue",
Content: prologueContent,
}},
})
if err != nil {
return fmt.Errorf("failed to send passkey response: %w", err)
}
cli.passkeyHandoffKey.Store(nil)
return nil
}
func (cli *Client) tryHandlePasskeyContinuationNotification(ctx context.Context, node *waBinary.Node) {
if fromJID := node.AttrGetter().JID("from"); fromJID != types.ServerJID {
cli.Log.Warnf("Ignoring passkey continuation notification from non-server JID %s", fromJID)
return
}
err := cli.handlePasskeyContinuationNotification(ctx, node)
if err != nil {
cli.Log.Warnf("Failed to handle passkey continuation notification: %v", err)
cli.dispatchEvent(&events.PairPasskeyError{
Error: err,
Continuation: true,
})
}
}
func (cli *Client) handlePasskeyContinuationNotification(ctx context.Context, node *waBinary.Node) error {
cache := cli.passkeyLinkingCache.Load()
if cache == nil {
return fmt.Errorf("received passkey continuation notification without a linking cache")
}
primaryEphemeralIdentity, err := parsePasskeyContinuationNotification(node)
if err != nil {
return fmt.Errorf("failed to parse passkey continuation notification: %w", err)
}
sharedSecret, err := curve25519.X25519(cache.keyPair.Priv[:], primaryEphemeralIdentity.PublicKey)
if err != nil {
return fmt.Errorf("failed to compute shared secret: %w", err)
}
_, err = cli.sendIQ(ctx, infoQuery{
Namespace: "md",
Type: iqSet,
To: types.ServerJID,
Content: []waBinary.Node{{
Tag: "companion_nonce",
Content: cache.companionNonce,
}},
})
if err != nil {
return fmt.Errorf("failed to send companion nonce: %w", err)
}
const info = "Pairing Information Encryption Key"
salt := fmt.Sprintf("Companion Pairing %d with ref %s", cache.deviceType, cache.pairingRef)
cache.encryptionKey = hkdfutil.SHA256(sharedSecret, []byte(salt), []byte(info), 32)
digest := sha256.Sum256(append(cache.companionNonce, primaryEphemeralIdentity.PublicKey...))
codeBytes := make([]byte, 5)
for i := range codeBytes {
codeBytes[i] = primaryEphemeralIdentity.Nonce[i] ^ digest[i]
}
encodedCode := linkingBase32.EncodeToString(codeBytes)
cli.dispatchEvent(&events.PairPasskeyConfirmation{
Code: encodedCode[0:4] + "-" + encodedCode[4:],
SkipHandoffUX: cli.passkeySkipHandoffUX.Load(),
})
return nil
}
// SendPasskeyConfirmation sends a confirmation to the server that the pairing code in [*events.PairPasskeyConfirmation]
// was shown to the user and they confirmed it. If the event has the SkipHandoffUX flag, showing the code to the user
// can be skipped.
func (cli *Client) SendPasskeyConfirmation(ctx context.Context) error {
cache := cli.passkeyLinkingCache.Load()
if cache == nil {
return fmt.Errorf("no passkey linking cache available")
} else if cache.encryptionKey == nil {
return fmt.Errorf("passkey linking cache does not have an encryption key yet")
}
req, err := proto.Marshal(&waCompanionReg.PairingRequest{
CompanionPublicKey: cli.Store.NoiseKey.Pub[:],
CompanionIdentityKey: cli.Store.IdentityKey.Pub[:],
AdvSecret: cli.Store.AdvSecretKey,
})
if err != nil {
return fmt.Errorf("failed to marshal PairingRequest: %w", err)
}
iv := random.Bytes(12)
encryptedReq, err := gcmutil.Encrypt(cache.encryptionKey, iv, req, nil)
if err != nil {
return fmt.Errorf("failed to encrypt PairingRequest: %w", err)
}
wrappedReq, err := proto.Marshal(&waCompanionReg.EncryptedPairingRequest{
EncryptedPayload: encryptedReq,
IV: iv,
})
if err != nil {
return fmt.Errorf("failed to marshal EncryptedPairingRequest: %w", err)
}
_, err = cli.sendIQ(ctx, infoQuery{
Namespace: "md",
Type: iqSet,
To: types.ServerJID,
Content: []waBinary.Node{{
Tag: "encrypted_pairing_request",
Content: wrappedReq,
}},
})
if err != nil {
return err
}
cli.passkeyLinkingCache.Store(nil)
return nil
}
func (cli *Client) getCompanionRef(ctx context.Context) (string, error) {
resp, err := cli.sendIQ(ctx, infoQuery{
Namespace: "md",
Type: iqGet,
To: types.ServerJID,
Content: []waBinary.Node{{Tag: "ref"}},
})
if err != nil {
return "", err
}
ref, ok := resp.GetOptionalChildByTag("ref")
if !ok {
return "", &ElementMissingError{Tag: "ref", In: "get ref response"}
}
contentBytes, ok := ref.Content.([]byte)
if !ok {
return "", fmt.Errorf("unexpected content type %T for <ref> node", ref.Content)
}
return string(contentBytes), nil
}
func (cli *Client) getPasskeyRequestOptions(ctx context.Context) (*types.WebAuthnPublicKey, error) {
resp, err := cli.sendIQ(ctx, infoQuery{
Namespace: "md",
Type: iqGet,
To: types.ServerJID,
Content: []waBinary.Node{{Tag: "passkey_request_options"}},
})
if err != nil {
return nil, err
}
return parsePasskeyNotification(resp)
}
func parsePasskeyNotification(node *waBinary.Node) (*types.WebAuthnPublicKey, error) {
opts, ok := node.GetOptionalChildByTag("passkey_request_options")
if !ok {
return nil, &ElementMissingError{Tag: "passkey_request_options", In: "passkey notification"}
}
content, ok := opts.Content.([]byte)
if !ok {
return nil, fmt.Errorf("unexpected content type %T for <passkey_request_options> node", opts.Content)
}
var pubKey types.WebAuthnPublicKey
err := json.Unmarshal(content, &pubKey)
if err != nil {
return nil, fmt.Errorf("failed to unmarshal <passkey_request_options> content: %w", err)
}
return &pubKey, nil
}
func parsePasskeyContinuationNotification(node *waBinary.Node) (*waCompanionReg.PrimaryEphemeralIdentity, error) {
opts, ok := node.GetOptionalChildByTag("primary_ephemeral_identity")
if !ok {
return nil, &ElementMissingError{Tag: "primary_ephemeral_identity", In: "passkey continuation notification"}
}
content, ok := opts.Content.([]byte)
if !ok {
return nil, fmt.Errorf("unexpected content type %T for <primary_ephemeral_identity> node", opts.Content)
}
var buf waCompanionReg.PrimaryEphemeralIdentity
err := proto.Unmarshal(content, &buf)
if err != nil {
return nil, fmt.Errorf("failed to unmarshal primary ephemeral identity: %w", err)
} else if len(buf.PublicKey) != 32 {
return nil, fmt.Errorf("unexpected public key length %d primary ephemeral identity", len(buf.PublicKey))
} else if len(buf.Nonce) != 32 {
return nil, fmt.Errorf("unexpected nonce length %d primary ephemeral identity", len(buf.Nonce))
}
return &buf, err
}