Add the Darwin_SecRandom entropy source

It uses the SecRandomCopyBytes function from the Security framework of
OS X and iOS. We need this because it is the official way to get
cryptographically secure random numbers on iOS, where /dev/random is not
accessible due to sandboxing.

4 files changed, 84 insertions, 0 deletions

diff --git a/src/lib/entropy/darwin_secrandom/darwin_secrandom.cpp b/src/lib/entropy/darwin_secrandom/darwin_secrandom.cpp
new file mode 100644
index 000000000..f04b75a12
--- /dev/null
+++ b/src/lib/entropy/darwin_secrandom/darwin_secrandom.cpp
@@ -0,0 +1,28 @@
+/*
+* Darwin SecRandomCopyBytes EntropySource
+* (C) 2015 Daniel Seither (Kullo GmbH)
+*
+* Botan is released under the Simplified BSD License (see license.txt)
+*/
+
+#include <botan/internal/darwin_secrandom.h>
+#include <Security/Security.h>
+
+namespace Botan {
+
+/**
+* Gather entropy from SecRandomCopyBytes
+*/
+void Darwin_SecRandom::poll(Entropy_Accumulator& accum)
+   {
+   const size_t ENTROPY_BITS_PER_BYTE = 8;
+   const size_t BUF_SIZE = 256;
+
+   m_buf.resize(BUF_SIZE);
+   if (0 == SecRandomCopyBytes(kSecRandomDefault, m_buf.size(), m_buf.data()))
+      {
+      accum.add(m_buf.data(), m_buf.size(), ENTROPY_BITS_PER_BYTE);
+      }
+   }
+
+}
diff --git a/src/lib/entropy/darwin_secrandom/darwin_secrandom.h b/src/lib/entropy/darwin_secrandom/darwin_secrandom.h
new file mode 100644
index 000000000..504d5cc64
--- /dev/null
+++ b/src/lib/entropy/darwin_secrandom/darwin_secrandom.h
@@ -0,0 +1,31 @@
+/*
+* Darwin SecRandomCopyBytes EntropySource
+* (C) 2015 Daniel Seither (Kullo GmbH)
+*
+* Botan is released under the Simplified BSD License (see license.txt)
+*/
+
+#ifndef BOTAN_ENTROPY_SRC_DARWIN_SECRANDOM_H__
+#define BOTAN_ENTROPY_SRC_DARWIN_SECRANDOM_H__
+
+#include <botan/entropy_src.h>
+
+namespace Botan {
+
+/**
+* Entropy source using SecRandomCopyBytes from Darwin's Security.framework
+*/
+class Darwin_SecRandom : public EntropySource
+   {
+   public:
+      std::string name() const override { return "Darwin SecRandomCopyBytes"; }
+
+      void poll(Entropy_Accumulator& accum) override;
+
+   private:
+      secure_vector<byte> m_buf;
+   };
+
+}
+
+#endif
diff --git a/src/lib/entropy/darwin_secrandom/info.txt b/src/lib/entropy/darwin_secrandom/info.txt
new file mode 100644
index 000000000..e12c341fd
--- /dev/null
+++ b/src/lib/entropy/darwin_secrandom/info.txt
@@ -0,0 +1,17 @@
+define ENTROPY_SRC_DARWIN_SECRANDOM 20150925
+
+<source>
+darwin_secrandom.cpp
+</source>
+
+<header:internal>
+darwin_secrandom.h
+</header:internal>
+
+<os>
+darwin
+</os>
+
+<frameworks>
+darwin -> Security
+</frameworks>
\ No newline at end of file
diff --git a/src/lib/entropy/entropy_srcs.cpp b/src/lib/entropy/entropy_srcs.cpp
index d44ab8c92..d57160c88 100644
--- a/src/lib/entropy/entropy_srcs.cpp
+++ b/src/lib/entropy/entropy_srcs.cpp
@@ -43,6 +43,10 @@
   #include <botan/internal/proc_walk.h>
 #endif
 
+#if defined(BOTAN_HAS_ENTROPY_SRC_DARWIN_SECRANDOM)
+  #include <botan/internal/darwin_secrandom.h>
+#endif
+
 namespace Botan {
 
 namespace {
@@ -97,6 +101,10 @@ std::vector<std::unique_ptr<EntropySource>> get_default_entropy_sources()
       ));
 #endif
 
+#if defined(BOTAN_HAS_ENTROPY_SRC_DARWIN_SECRANDOM)
+   sources.push_back(std::unique_ptr<EntropySource>(new Darwin_SecRandom));
+#endif
+
    return sources;
    }