Refactor random data generation

Add new RandomDataProvider object and implement existing random number
generation in terms of that.  This enables end users to supply their
own random data providers.

1 files changed, 49 insertions, 0 deletions

diff --git a/libqpdf/InsecureRandomDataProvider.cc b/libqpdf/InsecureRandomDataProvider.cc
new file mode 100644
index 00000000..5f637746
--- /dev/null
+++ b/libqpdf/InsecureRandomDataProvider.cc
@@ -0,0 +1,49 @@
+#include <qpdf/InsecureRandomDataProvider.hh>
+
+#include <qpdf/qpdf-config.h>
+#include <qpdf/QUtil.hh>
+#include <stdlib.h>
+
+InsecureRandomDataProvider::InsecureRandomDataProvider() :
+    seeded_random(false)
+{
+}
+
+InsecureRandomDataProvider::~InsecureRandomDataProvider()
+{
+}
+
+void
+InsecureRandomDataProvider::provideRandomData(unsigned char* data, size_t len)
+{
+    for (size_t i = 0; i < len; ++i)
+    {
+        data[i] = static_cast<unsigned char>((this->random() & 0xff0) >> 4);
+    }
+}
+
+long
+InsecureRandomDataProvider::random()
+{
+    if (! this->seeded_random)
+    {
+	// Seed the random number generator with something simple, but
+	// just to be interesting, don't use the unmodified current
+	// time.  It would be better if this were a more secure seed.
+        QUtil::srandom(QUtil::get_current_time() ^ 0xcccc);
+	this->seeded_random = true;
+    }
+
+#  ifdef HAVE_RANDOM
+    return ::random();
+#  else
+    return rand();
+#  endif
+}
+
+RandomDataProvider*
+InsecureRandomDataProvider::getInstance()
+{
+    static InsecureRandomDataProvider instance;
+    return &instance;
+}