Add scrypt-based password stretching.

Bug: 27056334
Change-Id: Ifa7f776c21c439f89dad7836175fbd045e1c603e

Android.mk

@@ -29,6 +29,7 @@ common_src_files := \
 	TrimTask.cpp \
 	Keymaster.cpp \
 	KeyStorage.cpp \
+	ScryptParameters.cpp \
 	secontext.cpp \
 
 common_c_includes := \

Ext4Crypt.cpp

@@ -42,13 +42,9 @@
 #include "cryptfs.h"
 #include "ext4_crypt.h"
 
-#define LOG_TAG "Ext4Crypt"
-
 #define EMULATED_USES_SELINUX 0
 
 #include <cutils/fs.h>
-#include <cutils/log.h>
-#include <cutils/klog.h>
 
 #include <android-base/file.h>
 #include <android-base/logging.h>

KeyStorage.cpp

@@ -17,6 +17,7 @@
 #include "KeyStorage.h"
 
 #include "Keymaster.h"
+#include "ScryptParameters.h"
 #include "Utils.h"
 
 #include <vector>
@@ -32,8 +33,16 @@
 #include <android-base/file.h>
 #include <android-base/logging.h>
 
+#include <cutils/properties.h>
+
 #include <keymaster/authorization_set.h>
 
+extern "C" {
+
+#include "crypto_scrypt.h"
+
+}
+
 namespace android {
 namespace vold {
 
@@ -42,14 +51,19 @@ const KeyAuthentication kEmptyAuthentication { "", "" };
 static constexpr size_t AES_KEY_BYTES = 32;
 static constexpr size_t GCM_NONCE_BYTES = 12;
 static constexpr size_t GCM_MAC_BYTES = 16;
-// FIXME: better name than "secdiscardable" sought!
+static constexpr size_t SALT_BYTES = 1<<4;
 static constexpr size_t SECDISCARDABLE_BYTES = 1<<14;
+static constexpr size_t STRETCHED_BYTES = 1<<6;
 
 static const char* kCurrentVersion = "1";
 static const char* kRmPath = "/system/bin/rm";
 static const char* kSecdiscardPath = "/system/bin/secdiscard";
+static const char* kStretch_none = "none";
+static const char* kStretch_nopassword = "nopassword";
+static const std::string kStretchPrefix_scrypt = "scrypt ";
 static const char* kFn_encrypted_key = "encrypted_key";
 static const char* kFn_keymaster_key_blob = "keymaster_key_blob";
+static const char* kFn_salt = "salt";
 static const char* kFn_secdiscardable = "secdiscardable";
 static const char* kFn_stretching = "stretching";
 static const char* kFn_version = "version";
@@ -165,15 +179,64 @@ static bool writeStringToFile(const std::string &payload, const std::string &fil
     return true;
 }
 
-static keymaster::AuthorizationSet buildParams(
-        const KeyAuthentication &auth, const std::string &secdiscardable) {
+static std::string getStretching() {
+    char paramstr[PROPERTY_VALUE_MAX];
+
+    property_get(SCRYPT_PROP, paramstr, SCRYPT_DEFAULTS);
+    return std::string() + kStretchPrefix_scrypt + paramstr;
+}
+
+static bool stretchingNeedsSalt(const std::string &stretching) {
+    return stretching != kStretch_nopassword && stretching != kStretch_none;
+}
+
+static bool stretchSecret(const std::string &stretching, const std::string &secret,
+        const std::string &salt, std::string &stretched) {
+    if (stretching == kStretch_nopassword) {
+        if (!secret.empty()) {
+            LOG(ERROR) << "Password present but stretching is nopasswd";
+            // Continue anyway
+        }
+        stretched.clear();
+    } else if (stretching == kStretch_none) {
+        stretched = secret;
+    } else if (std::equal(kStretchPrefix_scrypt.begin(),
+            kStretchPrefix_scrypt.end(), stretching.begin())) {
+        int Nf, rf, pf;
+        if (!parse_scrypt_parameters(
+                stretching.substr(kStretchPrefix_scrypt.size()).c_str(), &Nf, &rf, &pf)) {
+            LOG(ERROR) << "Unable to parse scrypt params in stretching: " << stretching;
+            return false;
+        }
+        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) {
+            LOG(ERROR) << "scrypt failed with params: " << stretching;
+            return false;
+        }
+    } else {
+        LOG(ERROR) << "Unknown stretching type: " << stretching;
+        return false;
+    }
+    return true;
+}
+
+static bool buildParams(const KeyAuthentication &auth, const std::string &stretching,
+        const std::string &salt, const std::string &secdiscardable,
+        keymaster::AuthorizationSet &result) {
+    std::string stretched;
+    if (!stretchSecret(stretching, auth.secret, salt, stretched)) return false;
+    auto appId = hashSecdiscardable(secdiscardable) + stretched;
     keymaster::AuthorizationSetBuilder paramBuilder;
-    auto appId = hashSecdiscardable(secdiscardable) + auth.secret;
     addStringParam(paramBuilder, keymaster::TAG_APPLICATION_ID, appId);
     if (!auth.token.empty()) {
         addStringParam(paramBuilder, keymaster::TAG_AUTH_TOKEN, auth.token);
     }
-    return paramBuilder.build();
+    result = paramBuilder.build();
+    return true;
 }
 
 bool storeKey(const std::string &dir, const KeyAuthentication &auth, const std::string &key) {
@@ -189,17 +252,24 @@ bool storeKey(const std::string &dir, const KeyAuthentication &auth, const std::
         return false;
     }
     if (!writeStringToFile(secdiscardable, dir + "/" + kFn_secdiscardable)) return false;
-    // Future proofing for when we add key stretching per b/27056334
-    auto stretching = auth.secret.empty() ? "nopassword" : "none";
+    std::string stretching = auth.secret.empty() ? kStretch_nopassword : getStretching();
     if (!writeStringToFile(stretching, dir + "/" +  kFn_stretching)) return false;
-    auto extraParams = buildParams(auth, secdiscardable);
+    std::string salt;
+    if (stretchingNeedsSalt(stretching)) {
+        if (ReadRandomBytes(SALT_BYTES, salt) != OK) {
+            LOG(ERROR) << "Random read failed";
+            return false;
+        }
+        if (!writeStringToFile(salt, dir + "/" +  kFn_salt)) return false;
+    }
+    keymaster::AuthorizationSet extraParams;
+    if (!buildParams(auth, stretching, salt, secdiscardable, extraParams)) return false;
     Keymaster keymaster;
     if (!keymaster) return false;
     std::string kmKey;
     if (!generateKeymasterKey(keymaster, extraParams, kmKey)) return false;
     std::string encryptedKey;
-    if (!encryptWithKeymasterKey(
-        keymaster, kmKey, extraParams, key, encryptedKey)) return false;
+    if (!encryptWithKeymasterKey(keymaster, kmKey, extraParams, key, encryptedKey)) return false;
     if (!writeStringToFile(kmKey, dir + "/" + kFn_keymaster_key_blob)) return false;
     if (!writeStringToFile(encryptedKey, dir + "/" + kFn_encrypted_key)) return false;
     return true;
@@ -214,7 +284,14 @@ bool retrieveKey(const std::string &dir, const KeyAuthentication &auth, std::str
     }
     std::string secdiscardable;
     if (!readFileToString(dir + "/" + kFn_secdiscardable, secdiscardable)) return false;
-    auto extraParams = buildParams(auth, secdiscardable);
+    std::string stretching;
+    if (!readFileToString(dir + "/" + kFn_stretching, stretching)) return false;
+    std::string salt;
+    if (stretchingNeedsSalt(stretching)) {
+        if (!readFileToString(dir + "/" +  kFn_salt, salt)) return false;
+    }
+    keymaster::AuthorizationSet extraParams;
+    if (!buildParams(auth, stretching, salt, secdiscardable, extraParams)) return false;
     std::string kmKey;
     if (!readFileToString(dir + "/" + kFn_keymaster_key_blob, kmKey)) return false;
     std::string encryptedMessage;

ScryptParameters.cpp

@@ -0,0 +1,50 @@
+/*
+ * Copyright (C) 2016 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "ScryptParameters.h"
+
+#include <stdlib.h>
+#include <string.h>
+
+bool parse_scrypt_parameters(const char* paramstr, int *Nf, int *rf, int *pf) {
+    int params[3];
+    char *token;
+    char *saveptr;
+    int i;
+
+    /*
+     * The token we're looking for should be three integers separated by
+     * colons (e.g., "12:8:1"). Scan the property to make sure it matches.
+     */
+    for (i = 0, token = strtok_r(const_cast<char *>(paramstr), ":", &saveptr);
+            token != nullptr && i < 3;
+            i++, token = strtok_r(nullptr, ":", &saveptr)) {
+        char *endptr;
+        params[i] = strtol(token, &endptr, 10);
+
+        /*
+         * Check that there was a valid number and it's 8-bit.
+         */
+        if ((*token == '\0') || (*endptr != '\0') || params[i] < 0 || params[i] > 255) {
+            return false;
+        }
+    }
+    if (token != nullptr) {
+        return false;
+    }
+    *Nf = params[0]; *rf = params[1]; *pf = params[2];
+    return true;
+}

ScryptParameters.h

@@ -0,0 +1,32 @@
+/*
+ * Copyright (C) 2016 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef ANDROID_VOLD_SCRYPT_PARAMETERS_H
+#define ANDROID_VOLD_SCRYPT_PARAMETERS_H
+
+#include <stdbool.h>
+#include <sys/cdefs.h>
+
+#define SCRYPT_PROP "ro.crypto.scrypt_params"
+#define SCRYPT_DEFAULTS "15:3:1"
+
+__BEGIN_DECLS
+
+bool parse_scrypt_parameters(const char* paramstr, int *Nf, int *rf, int *pf);
+
+__END_DECLS
+
+#endif

cryptfs.c

@@ -52,6 +52,7 @@
 #include "cutils/android_reboot.h"
 #include "hardware_legacy/power.h"
 #include <logwrap/logwrap.h>
+#include "ScryptParameters.h"
 #include "VolumeManager.h"
 #include "VoldUtil.h"
 #include "crypto_scrypt.h"
@@ -475,48 +476,17 @@ static void ioctl_init(struct dm_ioctl *io, size_t dataSize, const char *name, u
  * given device.
  */
 static void get_device_scrypt_params(struct crypt_mnt_ftr *ftr) {
-    const int default_params[] = SCRYPT_DEFAULTS;
-    int params[] = SCRYPT_DEFAULTS;
     char paramstr[PROPERTY_VALUE_MAX];
-    char *token;
-    char *saveptr;
-    int i;
-
-    property_get(SCRYPT_PROP, paramstr, "");
-    if (paramstr[0] != '\0') {
-        /*
-         * The token we're looking for should be three integers separated by
-         * colons (e.g., "12:8:1"). Scan the property to make sure it matches.
-         */
-        for (i = 0, token = strtok_r(paramstr, ":", &saveptr);
-                token != NULL && i < 3;
-                i++, token = strtok_r(NULL, ":", &saveptr)) {
-            char *endptr;
-            params[i] = strtol(token, &endptr, 10);
-
-            /*
-             * Check that there was a valid number and it's 8-bit. If not,
-             * break out and the end check will take the default values.
-             */
-            if ((*token == '\0') || (*endptr != '\0') || params[i] < 0 || params[i] > 255) {
-                break;
-            }
-        }
+    int Nf, rf, pf;
 
-        /*
-         * If there were not enough tokens or a token was malformed (not an
-         * integer), it will end up here and the default parameters can be
-         * taken.
-         */
-        if ((i != 3) || (token != NULL)) {
-            SLOGW("bad scrypt parameters '%s' should be like '12:8:1'; using defaults", paramstr);
-            memcpy(params, default_params, sizeof(params));
-        }
+    property_get(SCRYPT_PROP, paramstr, SCRYPT_DEFAULTS);
+    if (!parse_scrypt_parameters(paramstr, &Nf, &rf, &pf)) {
+        SLOGW("bad scrypt parameters '%s' should be like '12:8:1'; using defaults", paramstr);
+        parse_scrypt_parameters(SCRYPT_DEFAULTS, &Nf, &rf, &pf);
     }
-
-    ftr->N_factor = params[0];
-    ftr->r_factor = params[1];
-    ftr->p_factor = params[2];
+    ftr->N_factor = Nf;
+    ftr->r_factor = rf;
+    ftr->p_factor = pf;
 }
 
 static unsigned int get_fs_size(char *dev)

cryptfs.h

@@ -76,9 +76,6 @@
 #define CRYPT_MNT_MAGIC 0xD0B5B1C4
 #define PERSIST_DATA_MAGIC 0xE950CD44
 
-#define SCRYPT_PROP "ro.crypto.scrypt_params"
-#define SCRYPT_DEFAULTS { 15, 3, 1 }
-
 /* Key Derivation Function algorithms */
 #define KDF_PBKDF2 1
 #define KDF_SCRYPT 2