android,libtailscale: implement key.HardwareAttestationKey (#694)
Use a KeyStore-backed key to store a hardware-bound private key. Updates https://github.com/tailscale/tailscale/issues/15830 Signed-off-by: Andrew Lytvynov <awly@tailscale.com>mjf/bumposs
Andrew Lytvynov
3 months ago
committed by
GitHub
parent
0de26e52c0
commit
11869b00c5
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// Copyright (c) Tailscale Inc & AUTHORS
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// SPDX-License-Identifier: BSD-3-Clause
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package com.tailscale.ipn.util
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import android.content.pm.PackageManager
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import android.os.Build
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import android.security.keystore.KeyGenParameterSpec
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import android.security.keystore.KeyProperties
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import java.security.KeyPair
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import java.security.KeyPairGenerator
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import java.security.KeyStore
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import java.security.Signature
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import kotlin.random.Random
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class NoSuchKeyException : Exception("no key found matching the provided ID")
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class HardwareKeysNotSupported : Exception("hardware-backed keys are not supported on this device")
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// HardwareKeyStore implements the callbacks necessary to implement key.HardwareAttestationKey on
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// the Go side. It uses KeyStore with a StrongBox processor.
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class HardwareKeyStore() {
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var keyStoreKeys = HashMap<String, KeyPair>();
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val keyStore: KeyStore = KeyStore.getInstance("AndroidKeyStore").apply {
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load(null)
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}
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@OptIn(ExperimentalStdlibApi::class)
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fun newID(): String {
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var id: String
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do {
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id = Random.nextBytes(4).toHexString()
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} while (keyStoreKeys.containsKey(id))
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return id
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}
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fun createKey(): String {
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if (Build.VERSION.SDK_INT < Build.VERSION_CODES.P) {
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throw HardwareKeysNotSupported()
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}
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val id = newID()
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val kpg: KeyPairGenerator = KeyPairGenerator.getInstance(
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KeyProperties.KEY_ALGORITHM_EC, "AndroidKeyStore"
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)
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val parameterSpec: KeyGenParameterSpec = KeyGenParameterSpec.Builder(
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id, KeyProperties.PURPOSE_SIGN or KeyProperties.PURPOSE_VERIFY
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).run {
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// Use DIGEST_NONE because hashing is done on the Go side.
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setDigests(KeyProperties.DIGEST_NONE)
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setIsStrongBoxBacked(true)
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build()
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}
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kpg.initialize(parameterSpec)
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val kp = kpg.generateKeyPair()
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keyStoreKeys[id] = kp
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return id
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}
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fun releaseKey(id: String) {
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keyStoreKeys.remove(id)
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}
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fun sign(id: String, data: ByteArray): ByteArray {
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val key = keyStoreKeys[id]
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if (key == null) {
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throw NoSuchKeyException()
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}
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// Use NONEwithECDSA because hashing is done on the Go side.
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return Signature.getInstance("NONEwithECDSA").run {
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initSign(key.private)
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update(data)
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sign()
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}
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}
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fun public(id: String): ByteArray {
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val key = keyStoreKeys[id]
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if (key == null) {
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throw NoSuchKeyException()
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}
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return key.public.encoded
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}
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fun load(id: String) {
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if (keyStoreKeys[id] != null) {
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// Already loaded.
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return
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}
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val entry: KeyStore.Entry = keyStore.getEntry(id, null)
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if (entry !is KeyStore.PrivateKeyEntry) {
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throw NoSuchKeyException()
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}
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keyStoreKeys[id] = KeyPair(entry.certificate.publicKey, entry.privateKey)
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}
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}
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@ -0,0 +1,91 @@
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// Copyright (c) Tailscale Inc & AUTHORS
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// SPDX-License-Identifier: BSD-3-Clause
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package libtailscale
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import (
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"crypto"
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"crypto/ecdsa"
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"crypto/x509"
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"encoding/json"
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"errors"
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"fmt"
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"io"
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"tailscale.com/types/key"
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)
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func emptyHardwareAttestationKey(appCtx AppContext) key.HardwareAttestationKey {
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return &hardwareAttestationKey{appCtx: appCtx}
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}
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func createHardwareAttestationKey(appCtx AppContext) (key.HardwareAttestationKey, error) {
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id, err := appCtx.HardwareAttestationKeyCreate()
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if err != nil {
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return nil, err
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}
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k := &hardwareAttestationKey{appCtx: appCtx, id: id}
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if err := k.fetchPublic(); err != nil {
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return nil, err
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}
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return k, nil
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}
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var hardwareAttestationKeyNotInitialized = errors.New("HardwareAttestationKey has not been initialized")
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type hardwareAttestationKey struct {
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appCtx AppContext
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id string
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// public key is always initialized in createHardwareAttestationKey and
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// UnmarshalJSON. It's only nil in emptyHardwareAttestationKey.
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public *ecdsa.PublicKey
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}
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func (k *hardwareAttestationKey) fetchPublic() error {
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if k.id == "" || k.appCtx == nil {
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return hardwareAttestationKeyNotInitialized
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}
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pubRaw, err := k.appCtx.HardwareAttestationKeyPublic(k.id)
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if err != nil {
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return fmt.Errorf("loading public key from KeyStore: %w", err)
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}
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pubAny, err := x509.ParsePKIXPublicKey(pubRaw)
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if err != nil {
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return fmt.Errorf("parsing public key: %w", err)
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}
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pub, ok := pubAny.(*ecdsa.PublicKey)
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if !ok {
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return fmt.Errorf("parsed key is %T, expected *ecdsa.PublicKey", pubAny)
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}
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k.public = pub
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return nil
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}
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func (k *hardwareAttestationKey) Public() crypto.PublicKey { return k.public }
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func (k *hardwareAttestationKey) Sign(rand io.Reader, digest []byte, opts crypto.SignerOpts) (signature []byte, err error) {
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if k.id == "" || k.appCtx == nil {
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return nil, hardwareAttestationKeyNotInitialized
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}
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return k.appCtx.HardwareAttestationKeySign(k.id, digest)
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}
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func (k *hardwareAttestationKey) MarshalJSON() ([]byte, error) { return json.Marshal(k.id) }
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func (k *hardwareAttestationKey) UnmarshalJSON(data []byte) error {
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if err := json.Unmarshal(data, &k.id); err != nil {
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return err
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}
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if err := k.appCtx.HardwareAttestationKeyLoad(k.id); err != nil {
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return fmt.Errorf("loading key with ID %q from KeyStore: %w", k.id, err)
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}
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return k.fetchPublic()
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}
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func (k *hardwareAttestationKey) Close() error {
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if k.id == "" || k.appCtx == nil {
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return hardwareAttestationKeyNotInitialized
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}
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return k.appCtx.HardwareAttestationKeyRelease(k.id)
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}
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