diff --git a/Ext4Crypt.cpp b/Ext4Crypt.cpp
index 98cb05e..0ade48d 100644
--- a/Ext4Crypt.cpp
+++ b/Ext4Crypt.cpp
@@ -127,18 +127,18 @@
     return std::string((char*)key_ref2, EXT4_KEY_DESCRIPTOR_SIZE);
 }
 
-static bool fill_key(const std::string& key, ext4_encryption_key& ext4_key)
+static bool fill_key(const std::string& key, ext4_encryption_key* ext4_key)
 {
     if (key.size() != EXT4_AES_256_XTS_KEY_SIZE) {
         LOG(ERROR) << "Wrong size key " << key.size();
         return false;
     }
-    static_assert(EXT4_AES_256_XTS_KEY_SIZE <= sizeof(ext4_key.raw),
+    static_assert(EXT4_AES_256_XTS_KEY_SIZE <= sizeof(ext4_key->raw),
                   "Key too long!");
-    ext4_key.mode = EXT4_ENCRYPTION_MODE_AES_256_XTS;
-    ext4_key.size = key.size();
-    memset(ext4_key.raw, 0, sizeof(ext4_key.raw));
-    memcpy(ext4_key.raw, key.data(), key.size());
+    ext4_key->mode = EXT4_ENCRYPTION_MODE_AES_256_XTS;
+    ext4_key->size = key.size();
+    memset(ext4_key->raw, 0, sizeof(ext4_key->raw));
+    memcpy(ext4_key->raw, key.data(), key.size());
     return true;
 }
 
@@ -153,10 +153,10 @@
 }
 
 // Get the keyring we store all keys in
-static bool e4crypt_keyring(key_serial_t& device_keyring)
+static bool e4crypt_keyring(key_serial_t* device_keyring)
 {
-    device_keyring = keyctl_search(KEY_SPEC_SESSION_KEYRING, "keyring", "e4crypt", 0);
-    if (device_keyring == -1) {
+    *device_keyring = keyctl_search(KEY_SPEC_SESSION_KEYRING, "keyring", "e4crypt", 0);
+    if (*device_keyring == -1) {
         PLOG(ERROR) << "Unable to find device keyring";
         return false;
     }
@@ -165,14 +165,14 @@
 
 // Install password into global keyring
 // Return raw key reference for use in policy
-static bool install_key(const std::string &key, std::string &raw_ref)
+static bool install_key(const std::string &key, std::string *raw_ref)
 {
     ext4_encryption_key ext4_key;
-    if (!fill_key(key, ext4_key)) return false;
-    raw_ref = generate_key_ref(ext4_key.raw, ext4_key.size);
-    auto ref = keyname(raw_ref);
+    if (!fill_key(key, &ext4_key)) return false;
+    *raw_ref = generate_key_ref(ext4_key.raw, ext4_key.size);
+    auto ref = keyname(*raw_ref);
     key_serial_t device_keyring;
-    if (!e4crypt_keyring(device_keyring)) return false;
+    if (!e4crypt_keyring(&device_keyring)) return false;
     key_serial_t key_id = add_key("logon", ref.c_str(),
                                   (void*)&ext4_key, sizeof(ext4_key),
                                   device_keyring);
@@ -198,9 +198,9 @@
     if (s_ce_key_raw_refs.count(user_id) != 0) return true;
     const auto ce_key_path = get_ce_key_path(user_id);
     std::string ce_key;
-    if (!android::vold::retrieveKey(ce_key_path, auth, ce_key)) return false;
+    if (!android::vold::retrieveKey(ce_key_path, auth, &ce_key)) return false;
     std::string ce_raw_ref;
-    if (!install_key(ce_key, ce_raw_ref)) return false;
+    if (!install_key(ce_key, &ce_raw_ref)) return false;
     s_ce_keys[user_id] = ce_key;
     s_ce_key_raw_refs[user_id] = ce_raw_ref;
     LOG(DEBUG) << "Installed ce key for user " << user_id;
@@ -216,8 +216,8 @@
     return true;
 }
 
-static bool random_key(std::string &key) {
-    if (android::vold::ReadRandomBytes(EXT4_AES_256_XTS_KEY_SIZE, key) != 0) {
+static bool random_key(std::string *key) {
+    if (android::vold::ReadRandomBytes(EXT4_AES_256_XTS_KEY_SIZE, *key) != 0) {
         // TODO status_t plays badly with PLOG, fix it.
         LOG(ERROR) << "Random read failed";
         return false;
@@ -251,8 +251,8 @@
 
 static bool create_and_install_user_keys(userid_t user_id, bool create_ephemeral) {
     std::string de_key, ce_key;
-    if (!random_key(de_key)) return false;
-    if (!random_key(ce_key)) return false;
+    if (!random_key(&de_key)) return false;
+    if (!random_key(&ce_key)) return false;
     if (create_ephemeral) {
         // If the key should be created as ephemeral, don't store it.
         s_ephemeral_users.insert(user_id);
@@ -265,10 +265,10 @@
                 kEmptyAuthentication, ce_key)) return false;
     }
     std::string de_raw_ref;
-    if (!install_key(de_key, de_raw_ref)) return false;
+    if (!install_key(de_key, &de_raw_ref)) return false;
     s_de_key_raw_refs[user_id] = de_raw_ref;
     std::string ce_raw_ref;
-    if (!install_key(ce_key, ce_raw_ref)) return false;
+    if (!install_key(ce_key, &ce_raw_ref)) return false;
     s_ce_keys[user_id] = ce_key;
     s_ce_key_raw_refs[user_id] = ce_raw_ref;
     LOG(DEBUG) << "Created keys for user " << user_id;
@@ -276,13 +276,13 @@
 }
 
 static bool lookup_key_ref(const std::map<userid_t, std::string> &key_map,
-        userid_t user_id, std::string &raw_ref) {
+        userid_t user_id, std::string *raw_ref) {
     auto refi = key_map.find(user_id);
     if (refi == key_map.end()) {
         LOG(ERROR) << "Cannot find key for " << user_id;
         return false;
     }
-    raw_ref = refi->second;
+    *raw_ref = refi->second;
     return true;
 }
 
@@ -327,9 +327,9 @@
         if (s_de_key_raw_refs.count(user_id) == 0) {
             auto key_path = de_dir + "/" + entry->d_name;
             std::string key;
-            if (!android::vold::retrieveKey(key_path, kEmptyAuthentication, key)) return false;
+            if (!android::vold::retrieveKey(key_path, kEmptyAuthentication, &key)) return false;
             std::string raw_ref;
-            if (!install_key(key, raw_ref)) return false;
+            if (!install_key(key, &raw_ref)) return false;
             s_de_key_raw_refs[user_id] = raw_ref;
             LOG(DEBUG) << "Installed de key for user " << user_id;
         }
@@ -351,16 +351,16 @@
     std::string device_key;
     if (path_exists(device_key_path)) {
         if (!android::vold::retrieveKey(device_key_path,
-                kEmptyAuthentication, device_key)) return false;
+                kEmptyAuthentication, &device_key)) return false;
     } else {
         LOG(INFO) << "Creating new key";
-        if (!random_key(device_key)) return false;
+        if (!random_key(&device_key)) return false;
         if (!store_key(device_key_path, device_key_temp,
                 kEmptyAuthentication, device_key)) return false;
     }
 
     std::string device_key_ref;
-    if (!install_key(device_key, device_key_ref)) {
+    if (!install_key(device_key, &device_key_ref)) {
         LOG(ERROR) << "Failed to install device key";
         return false;
     }
@@ -434,7 +434,7 @@
 static bool evict_key(const std::string &raw_ref) {
     auto ref = keyname(raw_ref);
     key_serial_t device_keyring;
-    if (!e4crypt_keyring(device_keyring)) return false;
+    if (!e4crypt_keyring(&device_keyring)) return false;
     auto key_serial = keyctl_search(device_keyring, "logon", ref.c_str(), 0);
     if (keyctl_revoke(key_serial) != 0) {
         PLOG(ERROR) << "Failed to revoke key with serial " << key_serial << " ref " << ref;
@@ -452,9 +452,9 @@
     bool success = true;
     s_ce_keys.erase(user_id);
     std::string raw_ref;
-    success &= lookup_key_ref(s_ce_key_raw_refs, user_id, raw_ref) && evict_key(raw_ref);
+    success &= lookup_key_ref(s_ce_key_raw_refs, user_id, &raw_ref) && evict_key(raw_ref);
     s_ce_key_raw_refs.erase(user_id);
-    success &= lookup_key_ref(s_de_key_raw_refs, user_id, raw_ref) && evict_key(raw_ref);
+    success &= lookup_key_ref(s_de_key_raw_refs, user_id, &raw_ref) && evict_key(raw_ref);
     s_de_key_raw_refs.erase(user_id);
     auto it = s_ephemeral_users.find(user_id);
     if (it != s_ephemeral_users.end()) {
@@ -496,12 +496,12 @@
     return true;
 }
 
-static bool parse_hex(const char *hex, std::string &result) {
+static bool parse_hex(const char *hex, std::string *result) {
     if (strcmp("!", hex) == 0) {
-        result = "";
+        *result = "";
         return true;
     }
-    if (android::vold::HexToStr(hex, result) != 0) {
+    if (android::vold::HexToStr(hex, *result) != 0) {
         LOG(ERROR) << "Invalid FBE hex string"; // Don't log the string for security reasons
         return false;
     }
@@ -515,9 +515,9 @@
     if (!e4crypt_is_native()) return true;
     if (s_ephemeral_users.count(user_id) != 0) return true;
     std::string token, old_secret, new_secret;
-    if (!parse_hex(token_hex, token)) return false;
-    if (!parse_hex(old_secret_hex, old_secret)) return false;
-    if (!parse_hex(new_secret_hex, new_secret)) return false;
+    if (!parse_hex(token_hex, &token)) return false;
+    if (!parse_hex(old_secret_hex, &old_secret)) return false;
+    if (!parse_hex(new_secret_hex, &new_secret)) return false;
     auto old_auth = old_secret.empty()
         ? kEmptyAuthentication
         : android::vold::KeyAuthentication(token, old_secret);
@@ -532,7 +532,7 @@
     auto ce_key = it->second;
     auto ce_key_path = get_ce_key_path(user_id);
     std::string trial_key;
-    if (!android::vold::retrieveKey(ce_key_path, old_auth, trial_key)) {
+    if (!android::vold::retrieveKey(ce_key_path, old_auth, &trial_key)) {
         LOG(WARNING) << "change_user_key wasn't given enough info to reconstruct the key";
     } else if (ce_key != trial_key) {
         LOG(WARNING) << "Reconstructed key != stored key";
@@ -553,8 +553,8 @@
             return true;
         }
         std::string token, secret;
-        if (!parse_hex(token_hex, token)) return false;
-        if (!parse_hex(secret_hex, secret)) return false;
+        if (!parse_hex(token_hex, &token)) return false;
+        if (!parse_hex(secret_hex, &secret)) return false;
         android::vold::KeyAuthentication auth(token, secret);
         if (!read_and_install_user_ce_key(user_id, auth)) {
             LOG(ERROR) << "Couldn't read key for " << user_id;
@@ -621,7 +621,7 @@
 
         if (e4crypt_is_native()) {
             std::string de_raw_ref;
-            if (!lookup_key_ref(s_de_key_raw_refs, user_id, de_raw_ref)) return false;
+            if (!lookup_key_ref(s_de_key_raw_refs, user_id, &de_raw_ref)) return false;
             if (!ensure_policy(de_raw_ref, system_de_path)) return false;
             if (!ensure_policy(de_raw_ref, misc_de_path)) return false;
             if (!ensure_policy(de_raw_ref, user_de_path)) return false;
@@ -643,7 +643,7 @@
 
         if (e4crypt_is_native()) {
             std::string ce_raw_ref;
-            if (!lookup_key_ref(s_ce_key_raw_refs, user_id, ce_raw_ref)) return false;
+            if (!lookup_key_ref(s_ce_key_raw_refs, user_id, &ce_raw_ref)) return false;
             if (!ensure_policy(ce_raw_ref, system_ce_path)) return false;
             if (!ensure_policy(ce_raw_ref, misc_ce_path)) return false;
             if (!ensure_policy(ce_raw_ref, media_ce_path)) return false;
diff --git a/KeyStorage.cpp b/KeyStorage.cpp
index 0cd0548..429411d 100644
--- a/KeyStorage.cpp
+++ b/KeyStorage.cpp
@@ -97,13 +97,13 @@
 
 static bool generateKeymasterKey(Keymaster &keymaster,
         const KeyAuthentication &auth, const std::string &appId,
-        std::string &key) {
+        std::string *key) {
     auto paramBuilder = keymaster::AuthorizationSetBuilder()
         .AesEncryptionKey(AES_KEY_BYTES * 8)
         .Authorization(keymaster::TAG_BLOCK_MODE, KM_MODE_GCM)
         .Authorization(keymaster::TAG_MIN_MAC_LENGTH, GCM_MAC_BYTES * 8)
         .Authorization(keymaster::TAG_PADDING, KM_PAD_NONE);
-    addStringParam(paramBuilder, keymaster::TAG_APPLICATION_ID, appId);
+    addStringParam(&paramBuilder, keymaster::TAG_APPLICATION_ID, appId);
     if (auth.token.empty()) {
         LOG(DEBUG) << "Creating key that doesn't need auth token";
         paramBuilder.Authorization(keymaster::TAG_NO_AUTH_REQUIRED);
@@ -128,10 +128,10 @@
         .Authorization(keymaster::TAG_BLOCK_MODE, KM_MODE_GCM)
         .Authorization(keymaster::TAG_MAC_LENGTH, GCM_MAC_BYTES * 8)
         .Authorization(keymaster::TAG_PADDING, KM_PAD_NONE);
-    addStringParam(paramBuilder, keymaster::TAG_APPLICATION_ID, appId);
+    addStringParam(&paramBuilder, keymaster::TAG_APPLICATION_ID, appId);
     if (!auth.token.empty()) {
         LOG(DEBUG) << "Supplying auth token to Keymaster";
-        addStringParam(paramBuilder, keymaster::TAG_AUTH_TOKEN, auth.token);
+        addStringParam(&paramBuilder, keymaster::TAG_AUTH_TOKEN, auth.token);
     }
     return paramBuilder;
 }
@@ -142,10 +142,10 @@
         const KeyAuthentication &auth,
         const std::string &appId,
         const std::string &message,
-        std::string &ciphertext) {
+        std::string *ciphertext) {
     auto params = beginParams(auth, appId).build();
     keymaster::AuthorizationSet outParams;
-    auto opHandle = keymaster.begin(KM_PURPOSE_ENCRYPT, key, params, outParams);
+    auto opHandle = keymaster.begin(KM_PURPOSE_ENCRYPT, key, params, &outParams);
     if (!opHandle) return false;
     keymaster_blob_t nonceBlob;
     if (!outParams.GetTagValue(keymaster::TAG_NONCE, &nonceBlob)) {
@@ -156,12 +156,12 @@
     std::string nonce(reinterpret_cast<const char *>(nonceBlob.data), nonceBlob.data_length);
     if (!checkSize("nonce", nonce.size(), GCM_NONCE_BYTES)) return false;
     std::string body;
-    if (!opHandle.updateCompletely(message, body)) return false;
+    if (!opHandle.updateCompletely(message, &body)) return false;
 
     std::string mac;
-    if (!opHandle.finishWithOutput(mac)) return false;
+    if (!opHandle.finishWithOutput(&mac)) return false;
     if (!checkSize("mac", mac.size(), GCM_MAC_BYTES)) return false;
-    ciphertext = nonce + body + mac;
+    *ciphertext = nonce + body + mac;
     return true;
 }
 
@@ -171,7 +171,7 @@
         const KeyAuthentication &auth,
         const std::string &appId,
         const std::string &ciphertext,
-        std::string &message) {
+        std::string *message) {
     auto nonce = ciphertext.substr(0, GCM_NONCE_BYTES);
     auto bodyAndMac = ciphertext.substr(GCM_NONCE_BYTES);
     auto params = addStringParam(beginParams(auth, appId), keymaster::TAG_NONCE, nonce).build();
@@ -182,8 +182,8 @@
     return true;
 }
 
-static bool readFileToString(const std::string &filename, std::string &result) {
-    if (!android::base::ReadFileToString(filename, &result)) {
+static bool readFileToString(const std::string &filename, std::string *result) {
+    if (!android::base::ReadFileToString(filename, result)) {
          PLOG(ERROR) << "Failed to read from " << filename;
          return false;
     }
@@ -210,15 +210,15 @@
 }
 
 static bool stretchSecret(const std::string &stretching, const std::string &secret,
-        const std::string &salt, std::string &stretched) {
+        const std::string &salt, std::string *stretched) {
     if (stretching == kStretch_nopassword) {
         if (!secret.empty()) {
             LOG(WARNING) << "Password present but stretching is nopassword";
             // Continue anyway
         }
-        stretched.clear();
+        stretched->clear();
     } else if (stretching == kStretch_none) {
-        stretched = secret;
+        *stretched = secret;
     } else if (std::equal(kStretchPrefix_scrypt.begin(),
             kStretchPrefix_scrypt.end(), stretching.begin())) {
         int Nf, rf, pf;
@@ -227,12 +227,12 @@
             LOG(ERROR) << "Unable to parse scrypt params in stretching: " << stretching;
             return false;
         }
-        stretched.assign(STRETCHED_BYTES, '\0');
+        stretched->assign(STRETCHED_BYTES, '\0');
         if (crypto_scrypt(
                 reinterpret_cast<const uint8_t *>(secret.data()), secret.size(),
                 reinterpret_cast<const uint8_t *>(salt.data()), salt.size(),
                 1 << Nf, 1 << rf, 1 << pf,
-                reinterpret_cast<uint8_t *>(&stretched[0]), stretched.size()) != 0) {
+                reinterpret_cast<uint8_t *>(&(*stretched)[0]), stretched->size()) != 0) {
             LOG(ERROR) << "scrypt failed with params: " << stretching;
             return false;
         }
@@ -245,10 +245,10 @@
 
 static bool generateAppId(const KeyAuthentication &auth, const std::string &stretching,
         const std::string &salt, const std::string &secdiscardable,
-        std::string& result) {
+        std::string* appId) {
     std::string stretched;
-    if (!stretchSecret(stretching, auth.secret, salt, stretched)) return false;
-    result = hashSecdiscardable(secdiscardable) + stretched;
+    if (!stretchSecret(stretching, auth.secret, salt, &stretched)) return false;
+    *appId = hashSecdiscardable(secdiscardable) + stretched;
     return true;
 }
 
@@ -276,39 +276,39 @@
         if (!writeStringToFile(salt, dir + "/" +  kFn_salt)) return false;
     }
     std::string appId;
-    if (!generateAppId(auth, stretching, salt, secdiscardable, appId)) return false;
+    if (!generateAppId(auth, stretching, salt, secdiscardable, &appId)) return false;
     Keymaster keymaster;
     if (!keymaster) return false;
     std::string kmKey;
-    if (!generateKeymasterKey(keymaster, auth, appId, kmKey)) return false;
+    if (!generateKeymasterKey(keymaster, auth, appId, &kmKey)) return false;
     if (!writeStringToFile(kmKey, dir + "/" + kFn_keymaster_key_blob)) return false;
     std::string encryptedKey;
-    if (!encryptWithKeymasterKey(keymaster, kmKey, auth, appId, key, encryptedKey)) return false;
+    if (!encryptWithKeymasterKey(keymaster, kmKey, auth, appId, key, &encryptedKey)) return false;
     if (!writeStringToFile(encryptedKey, dir + "/" + kFn_encrypted_key)) return false;
     return true;
 }
 
-bool retrieveKey(const std::string &dir, const KeyAuthentication &auth, std::string &key) {
+bool retrieveKey(const std::string &dir, const KeyAuthentication &auth, std::string *key) {
     std::string version;
-    if (!readFileToString(dir + "/" + kFn_version, version)) return false;
+    if (!readFileToString(dir + "/" + kFn_version, &version)) return false;
     if (version != kCurrentVersion) {
         LOG(ERROR) << "Version mismatch, expected " << kCurrentVersion << " got " << version;
         return false;
     }
     std::string secdiscardable;
-    if (!readFileToString(dir + "/" + kFn_secdiscardable, secdiscardable)) return false;
+    if (!readFileToString(dir + "/" + kFn_secdiscardable, &secdiscardable)) return false;
     std::string stretching;
-    if (!readFileToString(dir + "/" + kFn_stretching, stretching)) return false;
+    if (!readFileToString(dir + "/" + kFn_stretching, &stretching)) return false;
     std::string salt;
     if (stretchingNeedsSalt(stretching)) {
-        if (!readFileToString(dir + "/" +  kFn_salt, salt)) return false;
+        if (!readFileToString(dir + "/" +  kFn_salt, &salt)) return false;
     }
     std::string appId;
-    if (!generateAppId(auth, stretching, salt, secdiscardable, appId)) return false;
+    if (!generateAppId(auth, stretching, salt, secdiscardable, &appId)) return false;
     std::string kmKey;
-    if (!readFileToString(dir + "/" + kFn_keymaster_key_blob, kmKey)) return false;
+    if (!readFileToString(dir + "/" + kFn_keymaster_key_blob, &kmKey)) return false;
     std::string encryptedMessage;
-    if (!readFileToString(dir + "/" + kFn_encrypted_key, encryptedMessage)) return false;
+    if (!readFileToString(dir + "/" + kFn_encrypted_key, &encryptedMessage)) return false;
     Keymaster keymaster;
     if (!keymaster) return false;
     return decryptWithKeymasterKey(keymaster, kmKey, auth, appId, encryptedMessage, key);
@@ -316,7 +316,7 @@
 
 static bool deleteKey(const std::string &dir) {
     std::string kmKey;
-    if (!readFileToString(dir + "/" + kFn_keymaster_key_blob, kmKey)) return false;
+    if (!readFileToString(dir + "/" + kFn_keymaster_key_blob, &kmKey)) return false;
     Keymaster keymaster;
     if (!keymaster) return false;
     if (!keymaster.deleteKey(kmKey)) return false;
diff --git a/KeyStorage.h b/KeyStorage.h
index 54c3b2c..6daf1d2 100644
--- a/KeyStorage.h
+++ b/KeyStorage.h
@@ -42,7 +42,7 @@
 bool storeKey(const std::string &dir, const KeyAuthentication &auth, const std::string &key);
 
 // Retrieve the key from the named directory.
-bool retrieveKey(const std::string &dir, const KeyAuthentication &auth, std::string &key);
+bool retrieveKey(const std::string &dir, const KeyAuthentication &auth, std::string *key);
 
 // Securely destroy the key stored in the named directory and delete the directory.
 bool destroyKey(const std::string &dir);
diff --git a/Keymaster.cpp b/Keymaster.cpp
index b3ece19..849ccf7 100644
--- a/Keymaster.cpp
+++ b/Keymaster.cpp
@@ -23,8 +23,8 @@
 
 bool KeymasterOperation::updateCompletely(
         const std::string &input,
-        std::string &output) {
-    output.clear();
+        std::string *output) {
+    output->clear();
     auto it = input.begin();
     while (it != input.end()) {
         size_t toRead = static_cast<size_t>(input.end() - it);
@@ -38,7 +38,7 @@
             mDevice = nullptr;
             return false;
         }
-        output.append(reinterpret_cast<const char *>(outputBlob.data), outputBlob.data_length);
+        output->append(reinterpret_cast<const char *>(outputBlob.data), outputBlob.data_length);
         free(const_cast<uint8_t *>(outputBlob.data));
         if (inputConsumed > toRead) {
             LOG(ERROR) << "update reported too much input consumed";
@@ -61,7 +61,7 @@
     return true;
 }
 
-bool KeymasterOperation::finishWithOutput(std::string &output) {
+bool KeymasterOperation::finishWithOutput(std::string *output) {
     keymaster_blob_t outputBlob;
     auto error = mDevice->finish(mDevice, mOpHandle,
         nullptr, nullptr, nullptr, &outputBlob);
@@ -70,7 +70,7 @@
         LOG(ERROR) << "finish failed, code " << error;
         return false;
     }
-    output.assign(reinterpret_cast<const char *>(outputBlob.data), outputBlob.data_length);
+    output->assign(reinterpret_cast<const char *>(outputBlob.data), outputBlob.data_length);
     free(const_cast<uint8_t *>(outputBlob.data));
     return true;
 }
@@ -98,14 +98,14 @@
 
 bool Keymaster::generateKey(
         const keymaster::AuthorizationSet &inParams,
-        std::string &key) {
+        std::string *key) {
     keymaster_key_blob_t keyBlob;
     auto error = mDevice->generate_key(mDevice, &inParams, &keyBlob, nullptr);
     if (error != KM_ERROR_OK) {
         LOG(ERROR) << "generate_key failed, code " << error;
         return false;
     }
-    key.assign(reinterpret_cast<const char *>(keyBlob.key_material), keyBlob.key_material_size);
+    key->assign(reinterpret_cast<const char *>(keyBlob.key_material), keyBlob.key_material_size);
     free(const_cast<uint8_t *>(keyBlob.key_material));
     return true;
 }
@@ -125,7 +125,7 @@
         keymaster_purpose_t purpose,
         const std::string &key,
         const keymaster::AuthorizationSet &inParams,
-        keymaster::AuthorizationSet &outParams) {
+        keymaster::AuthorizationSet *outParams) {
     keymaster_key_blob_t keyBlob { reinterpret_cast<const uint8_t *>(key.data()), key.size() };
     keymaster_operation_handle_t mOpHandle;
     keymaster_key_param_set_t outParams_set;
@@ -135,8 +135,8 @@
         LOG(ERROR) << "begin failed, code " << error;
         return KeymasterOperation(nullptr, mOpHandle);
     }
-    outParams.Clear();
-    outParams.push_back(outParams_set);
+    outParams->Clear();
+    outParams->push_back(outParams_set);
     keymaster_free_param_set(&outParams_set);
     return KeymasterOperation(mDevice, mOpHandle);
 }
diff --git a/Keymaster.h b/Keymaster.h
index a4deddf..dd20ef9 100644
--- a/Keymaster.h
+++ b/Keymaster.h
@@ -45,11 +45,11 @@
     explicit operator bool() {return mDevice != nullptr;}
     // Call "update" repeatedly until all of the input is consumed, and
     // concatenate the output. Return true on success.
-    bool updateCompletely(const std::string &input, std::string &output);
+    bool updateCompletely(const std::string &input, std::string *output);
     // Finish; pass nullptr for the "output" param.
     bool finish();
     // Finish and write the output to this string.
-    bool finishWithOutput(std::string &output);
+    bool finishWithOutput(std::string *output);
     // Move constructor
     KeymasterOperation(KeymasterOperation&& rhs) {
         mOpHandle = rhs.mOpHandle;
@@ -74,7 +74,7 @@
     // false if we failed to open the keymaster device.
     explicit operator bool() {return mDevice != nullptr;}
     // Generate a key in the keymaster from the given params.
-    bool generateKey(const AuthorizationSet &inParams, std::string &key);
+    bool generateKey(const AuthorizationSet &inParams, std::string *key);
     // If the keymaster supports it, permanently delete a key.
     bool deleteKey(const std::string &key);
     // Begin a new cryptographic operation, collecting output parameters.
@@ -82,7 +82,7 @@
             keymaster_purpose_t purpose,
             const std::string &key,
             const AuthorizationSet &inParams,
-            AuthorizationSet &outParams);
+            AuthorizationSet *outParams);
     // Begin a new cryptographic operation; don't collect output parameters.
     KeymasterOperation begin(
             keymaster_purpose_t purpose,
@@ -100,9 +100,9 @@
 }
 
 template <keymaster_tag_t Tag>
-inline void addStringParam(AuthorizationSetBuilder &params,
+inline void addStringParam(AuthorizationSetBuilder *params,
         TypedTag<KM_BYTES, Tag> tag, const std::string& val) {
-    params.Authorization(tag, val.data(), val.size());
+    params->Authorization(tag, val.data(), val.size());
 }
 
 }  // namespace vold