From 0b6a09b9cfd3898481d5c905944efc3e9bf18274 Mon Sep 17 00:00:00 2001
From: chriseth <c@ethdev.com>
Date: Tue, 16 Jun 2015 14:00:24 +0200
Subject: [PATCH] Nonce refactoring.

---
 libdevcrypto/Common.cpp   | 89 ++++++++++++++++++++++++++-------------
 libdevcrypto/Common.h     | 21 ++++++++-
 libdevcrypto/Exceptions.h |  2 +-
 3 files changed, 79 insertions(+), 33 deletions(-)

diff --git a/libdevcrypto/Common.cpp b/libdevcrypto/Common.cpp
index 8567ac12b..94f78b1e2 100644
--- a/libdevcrypto/Common.cpp
+++ b/libdevcrypto/Common.cpp
@@ -254,42 +254,71 @@ h256 crypto::kdf(Secret const& _priv, h256 const& _hash)
 	return s;
 }
 
-h256 Nonce::get(bool _commit)
+mutex Nonce::s_x;
+
+h256 Nonce::get()
 {
 	// todo: atomic efface bit, periodic save, kdf, rr, rng
 	// todo: encrypt
-	static h256 s_seed;
-	static string s_seedFile(getDataDir() + "/seed");
-	static mutex s_x;
-	Guard l(s_x);
-	if (!s_seed)
+	Guard l(Nonce::s_x);
+	return Nonce::singleton().next();
+}
+
+// get: Called for the first time: read seed hash from file (or generate)
+// before destruction: increment current value and store
+
+Nonce::~Nonce()
+{
+	Guard l(Nonce::s_x);
+	// These might throw.
+	next();
+	commit();
+}
+
+Nonce& Nonce::singleton()
+{
+	static Nonce s;
+	return s;
+}
+
+void Nonce::initialiseIfNeeded()
+{
+	if (m_value)
+		return;
+
+	bytes b = contents(seedFile());
+	if (b.size() == 32)
+		memcpy(m_value.data(), b.data(), 32);
+	else
 	{
-		static Nonce s_nonce;
-		bytes b = contents(s_seedFile);
-		if (b.size() == 32)
-			memcpy(s_seed.data(), b.data(), 32);
-		else
-		{
-			// todo: replace w/entropy from user and system
-			std::mt19937_64 s_eng(time(0) + chrono::high_resolution_clock::now().time_since_epoch().count());
-			std::uniform_int_distribution<uint16_t> d(0, 255);
-			for (unsigned i = 0; i < 32; ++i)
-				s_seed[i] = (byte)d(s_eng);
-		}
-		if (!s_seed)
-			BOOST_THROW_EXCEPTION(InvalidState());
-		
-		// prevent seed reuse if process terminates abnormally
-		try { writeFile(s_seedFile, bytes()); } catch (FileError const&) {}
+		// todo: replace w/entropy from user and system
+		std::mt19937_64 s_eng(time(0) + chrono::high_resolution_clock::now().time_since_epoch().count());
+		std::uniform_int_distribution<uint16_t> d(0, 255);
+		for (unsigned i = 0; i < 32; ++i)
+			m_value[i] = byte(d(s_eng));
 	}
-	h256 prev(s_seed);
-	sha3(prev.ref(), s_seed.ref());
-	if (_commit)
-		try { writeFile(s_seedFile, s_seed.asBytes()); } catch (FileError const&) {}
-	return std::move(s_seed);
+	if (!m_value)
+		BOOST_THROW_EXCEPTION(InvalidState());
+
+	// prevent seed reuse if process terminates abnormally
+	// this might throw
+	writeFile(seedFile(), bytes());
 }
 
-Nonce::~Nonce()
+h256 Nonce::next()
+{
+	initialiseIfNeeded();
+	m_value = sha3(m_value);
+	return m_value;
+}
+
+void Nonce::commit()
+{
+	// this might throw
+	writeFile(seedFile(), m_value.asBytes());
+}
+
+string Nonce::seedFile()
 {
-	Nonce::get(true);
+	return getDataDir() + "/seed";
 }
diff --git a/libdevcrypto/Common.h b/libdevcrypto/Common.h
index 7bb51e563..96f525e49 100644
--- a/libdevcrypto/Common.h
+++ b/libdevcrypto/Common.h
@@ -24,6 +24,7 @@
 
 #pragma once
 
+#include <mutex>
 #include <libdevcore/Common.h>
 #include <libdevcore/FixedHash.h>
 #include <libdevcore/Exceptions.h>
@@ -180,14 +181,30 @@ struct InvalidState: public dev::Exception {};
 h256 kdf(Secret const& _priv, h256 const& _hash);
 
 /**
- * @brief Generator for nonce material
+ * @brief Generator for nonce material.
  */
 struct Nonce
 {
-	static h256 get(bool _commit = false);
+	static h256 get();
 private:
 	Nonce() {}
 	~Nonce();
+	/// @returns the singleton instance.
+	static Nonce& singleton();
+	/// Reads the last seed from the seed file.
+	void initialiseIfNeeded();
+	/// @returns the next nonce.
+	h256 next();
+	/// Stores the current seed in the seed file.
+	void commit();
+	/// @returns the path of the seed file.
+	static std::string seedFile();
+
+	/// Mutex for the singleton object.
+	/// @note Every access to any private function has to be guarded by this mutex.
+	static std::mutex s_x;
+
+	h256 m_value;
 };
 }
 
diff --git a/libdevcrypto/Exceptions.h b/libdevcrypto/Exceptions.h
index 675213d8b..858374bda 100644
--- a/libdevcrypto/Exceptions.h
+++ b/libdevcrypto/Exceptions.h
@@ -29,7 +29,7 @@ namespace crypto
 {
 
 /// Rare malfunction of cryptographic functions.
-DEV_SIMPLE_EXCEPTION_RLP(CryptoException);
+DEV_SIMPLE_EXCEPTION(CryptoException);
 
 }
 }