Superencrypt authentication-bound keys.
This CL causes keystore to automatically encrypt all newly-created
keymaster key blobs which are authentication-bound. This appears on its
face to be pointless, since the sensitive key material in the key blobs
is already encrypted by the Trusted Execution Environment. It's not
pointless because this adds a cryptographic dependency on the user's
password, including any strengthening performed by
LockSettingService... which may include the use of a separate hardware
trusted module, separate from (and presumably more secure than) the TEE.
A better solution is planned for the next release, but that requires
changes to Gatekeeper and Keymaster. This superencryption will be
removed when that work is done.
Note that the encryption method used by keystore is weak. A separate CL will
replace the weak method with a proper authenticated encryption.
(cherry picked from commit 07aebe73053df12c21c7481a93146bd76add7fbd)
Test: Manual testing.
Bug: 35849499
Change-Id: I0c4910ea24b97bc8046f3d114bfb336670d03321
diff --git a/keystore/key_store_service.cpp b/keystore/key_store_service.cpp
index 434dddd..a28a35a 100644
--- a/keystore/key_store_service.cpp
+++ b/keystore/key_store_service.cpp
@@ -40,6 +40,7 @@
#include <keystore/keystore_hidl_support.h>
namespace keystore {
+
using namespace android;
namespace {
@@ -58,6 +59,10 @@
[&](auto& param) { return param.tag == tag; });
}
+bool isAuthenticationBound(const hidl_vec<KeyParameter>& params) {
+ return !containsTag(params, Tag::NO_AUTH_REQUIRED);
+}
+
std::pair<KeyStoreServiceReturnCode, bool> hadFactoryResetSinceIdRotation() {
struct stat sbuf;
if (stat(kTimestampFilePath, &sbuf) == 0) {
@@ -683,6 +688,9 @@
Blob keyBlob(&hidlKeyBlob[0], hidlKeyBlob.size(), NULL, 0, ::TYPE_KEYMASTER_10);
keyBlob.setFallback(usingFallback);
+ if (isAuthenticationBound(params)) {
+ keyBlob.setSuperEncrypted(true);
+ }
keyBlob.setEncrypted(flags & KEYSTORE_FLAG_ENCRYPTED);
error = mKeyStore->put(filename.string(), &keyBlob, get_user_id(uid));
@@ -827,6 +835,9 @@
Blob ksBlob(&keyBlob[0], keyBlob.size(), NULL, 0, ::TYPE_KEYMASTER_10);
ksBlob.setFallback(usingFallback);
+ if (isAuthenticationBound(params)) {
+ ksBlob.setSuperEncrypted(true);
+ }
ksBlob.setEncrypted(flags & KEYSTORE_FLAG_ENCRYPTED);
error = mKeyStore->put(filename.string(), &ksBlob, get_user_id(uid));
@@ -963,6 +974,9 @@
Blob keyBlob;
String8 name8(name);
result->resultCode = mKeyStore->getKeyForName(&keyBlob, name8, targetUid, TYPE_KEYMASTER_10);
+ if (result->resultCode == ResponseCode::LOCKED && keyBlob.isSuperEncrypted()) {
+ result->resultCode = ErrorCode::KEY_USER_NOT_AUTHENTICATED;
+ }
if (!result->resultCode.isOk()) {
return;
}