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

1 files changed, 16 insertions, 8 deletions

diff --git a/keystore/blob.cpp b/keystore/blob.cpp
index 7ee26f7..0e09262 100644
--- a/keystore/blob.cpp
+++ b/keystore/blob.cpp
@@ -71,12 +71,20 @@ bool Blob::isEncrypted() const {
     return mBlob.flags & KEYSTORE_FLAG_ENCRYPTED;
 }
 
+bool Blob::isSuperEncrypted() const {
+    return mBlob.flags & KEYSTORE_FLAG_SUPER_ENCRYPTED;
+}
+
+inline uint8_t setFlag(uint8_t flags, bool set, KeyStoreFlag flag) {
+    return set ? (flags | flag) : (flags & ~flag);
+}
+
 void Blob::setEncrypted(bool encrypted) {
-    if (encrypted) {
-        mBlob.flags |= KEYSTORE_FLAG_ENCRYPTED;
-    } else {
-        mBlob.flags &= ~KEYSTORE_FLAG_ENCRYPTED;
-    }
+    mBlob.flags = setFlag(mBlob.flags, encrypted, KEYSTORE_FLAG_ENCRYPTED);
+}
+
+void Blob::setSuperEncrypted(bool superEncrypted) {
+    mBlob.flags = setFlag(mBlob.flags, superEncrypted, KEYSTORE_FLAG_SUPER_ENCRYPTED);
 }
 
 void Blob::setFallback(bool fallback) {
@@ -90,7 +98,7 @@ void Blob::setFallback(bool fallback) {
 ResponseCode Blob::writeBlob(const char* filename, AES_KEY* aes_key, State state,
                              Entropy* entropy) {
     ALOGV("writing blob %s", filename);
-    if (isEncrypted()) {
+    if (isEncrypted() || isSuperEncrypted()) {
         if (state != STATE_NO_ERROR) {
             ALOGD("couldn't insert encrypted blob while not unlocked");
             return ResponseCode::LOCKED;
@@ -115,7 +123,7 @@ ResponseCode Blob::writeBlob(const char* filename, AES_KEY* aes_key, State state
 
     mBlob.length = htonl(mBlob.length);
 
-    if (isEncrypted()) {
+    if (isEncrypted() || isSuperEncrypted()) {
         MD5(mBlob.digested, digestedLength, mBlob.digest);
 
         uint8_t vector[AES_BLOCK_SIZE];
@@ -168,7 +176,7 @@ ResponseCode Blob::readBlob(const char* filename, AES_KEY* aes_key, State state)
         return ResponseCode::VALUE_CORRUPTED;
     }
 
-    if (isEncrypted() && (state != STATE_NO_ERROR)) {
+    if ((isEncrypted() || isSuperEncrypted()) && (state != STATE_NO_ERROR)) {
         return ResponseCode::LOCKED;
     }