[libcalamares] Add an Entropy service for getting random data

- Tries to get the "best" random data
 - Reports the quality of the random data it got

src/libcalamares/CMakeLists.txt

@@ -39,7 +39,7 @@ set( libSources
 
     # Modules
     modulesystem/InstanceKey.cpp
-    
+
     # Network service
     network/Manager.cpp
 
@@ -50,6 +50,7 @@ set( libSources
     utils/CalamaresUtilsSystem.cpp
     utils/CommandList.cpp
     utils/Dirs.cpp
+    utils/Entropy.cpp
     utils/Logger.cpp
     utils/PluginFactory.cpp
     utils/Retranslator.cpp

src/libcalamares/utils/Entropy.cpp

@@ -0,0 +1,75 @@
+/* === This file is part of Calamares - <https://github.com/calamares> ===
+ *
+ *   Copyright 2019-2020, Adriaan de Groot <groot@kde.org>
+ *
+ *   Calamares is free software: you can redistribute it and/or modify
+ *   it under the terms of the GNU General Public License as published by
+ *   the Free Software Foundation, either version 3 of the License, or
+ *   (at your option) any later version.
+ *
+ *   Calamares is distributed in the hope that it will be useful,
+ *   but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ *   GNU General Public License for more details.
+ *
+ *   You should have received a copy of the GNU General Public License
+ *   along with Calamares. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include "Entropy.h"
+
+#include <QFile>
+
+#include <random>
+
+CalamaresUtils::EntropySource
+CalamaresUtils::getEntropy( int size, QByteArray& b )
+{
+    b.clear();
+    b.resize( size );
+    char* buffer = b.data();
+    std::fill( buffer, buffer + size, 0xcb );
+
+    int readSize = 0;
+    QFile urandom( "/dev/urandom" );
+    if ( urandom.exists() && urandom.open( QIODevice::ReadOnly ) )
+    {
+        readSize = urandom.read( buffer, size );
+        urandom.close();
+    }
+
+    if ( readSize >= size )
+    {
+        return EntropySource::URandom;
+    }
+
+    // If it wasn't available, or did not return enough bytes,
+    // complete it with twister (and tell the client).
+    std::random_device r;
+    std::seed_seq seed { r(), r(), r(), r(), r(), r(), r(), r() };
+    std::mt19937_64 twister( seed );
+
+    std::uint64_t next = 0;
+
+    do
+    {
+        next = twister();
+        // Eight times, for a 64-bit next
+#define GET_ONE_BYTE \
+    if ( readSize < size ) \
+    { \
+        buffer[ readSize++ ] = next & 0xff; \
+        next = next >> 8; \
+    }
+        GET_ONE_BYTE
+        GET_ONE_BYTE
+        GET_ONE_BYTE
+        GET_ONE_BYTE
+        GET_ONE_BYTE
+        GET_ONE_BYTE
+        GET_ONE_BYTE
+        GET_ONE_BYTE
+    } while ( readSize < size );
+
+    return EntropySource::Twister;
+}

src/libcalamares/utils/Entropy.h

@@ -0,0 +1,44 @@
+/* === This file is part of Calamares - <https://github.com/calamares> ===
+ *
+ *   Copyright 2019-2020, Adriaan de Groot <groot@kde.org>
+ *
+ *   Calamares is free software: you can redistribute it and/or modify
+ *   it under the terms of the GNU General Public License as published by
+ *   the Free Software Foundation, either version 3 of the License, or
+ *   (at your option) any later version.
+ *
+ *   Calamares is distributed in the hope that it will be useful,
+ *   but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ *   GNU General Public License for more details.
+ *
+ *   You should have received a copy of the GNU General Public License
+ *   along with Calamares. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#ifndef UTILS_ENTROPY_H
+#define UTILS_ENTROPY_H
+
+#include "DllMacro.h"
+
+#include <QByteArray>
+
+namespace CalamaresUtils
+{
+/// @brief Which entropy source was actually used for the entropy.
+enum class EntropySource
+{
+    URandom,  ///< Read from /dev/urandom
+    Twister  ///< Generated by pseudo-random
+};
+
+/** @brief Fill buffer @p b with exactly @p size random bytes
+ *
+ * The array is cleared and resized, then filled with 0xcb
+ * "just in case", after which it is filled with random
+ * bytes from a suitable source. Returns which source was used.
+ */
+DLLEXPORT EntropySource getEntropy( int size, QByteArray& b );
+}  // namespace CalamaresUtils
+
+#endif