decrypt: AOSP 10 requires the use of fscrypt

fscrypt aosp doc: https://source.android.com/security/encryption/file-based
kernel fscrypt doc: https://www.kernel.org/doc/html/v4.18/filesystems/fscrypt.html

This commit implements the ability for TWRP to use fscrypt to decrypt
files on the fscrypt implementation. It has been implemented mostly
in a new successor library to e4crypt called libtwrpfscrypt. Most of the
code was ported from AOSP vold.

Notable updates include:
 - updated policy storage by libtar
 - lookup of fbe policies by libtwrpfscrypt
 - threaded keystore operations

Big thanks to Dees_Troy for the initial trailblazing
of encryption in TWRP.

Change-Id: I69cd2eba3693a9914e00213d4943229635d0cdae

crypto/fscrypt/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;
+}