From 8ba42323860a3978efa72bf0ef071b32407503e0 Mon Sep 17 00:00:00 2001
From: Jeffrey Walton <noloader@gmail.com>
Date: Sun, 29 Nov 2015 14:43:12 -0500
Subject: [PATCH] Changed retry count for RDRAND and RDSEED. RDSEED appears to
 fail to fulfill requests at about 6 to 8 times the rate of RDRAND.

---
 rdrand.cpp | 26 ++++++++++++++++++++++----
 rdrand.h   | 17 +++++++++++------
 2 files changed, 33 insertions(+), 10 deletions(-)

diff --git a/rdrand.cpp b/rdrand.cpp
index b14359fa..1fd6f94c 100644
--- a/rdrand.cpp
+++ b/rdrand.cpp
@@ -17,8 +17,8 @@
 //   indirectly uses CRYPTOPP_BOOL_{X86|X32|X64} (via CRYPTOPP_CPUID_AVAILABLE)
 //   to select an implementation or "throw NotImplemented". At runtime, the
 //   class uses the result of CPUID to determine if RDRAND or RDSEED are
-//   available. A lazy throw strategy is used in case the CPU does not support
-//   the instruction. I.e., the throw is deferred until GenerateBlock is called.
+//   available. If not available, a lazy throw strategy is used. I.e., the
+//   throw is deferred until GenerateBlock() is called.
 
 // Here's the naming convention for the functions....
 //   MSC = Microsoft Compiler (and compatibles)
@@ -196,7 +196,10 @@ static int ALL_RRI_GenerateBlock(byte *output, size_t size, unsigned int safety)
         else
         {
 			if (!safety--)
+			{
+				assert(0);
 				return 0;
+			}
         }
 	}
 
@@ -214,7 +217,10 @@ static int ALL_RRI_GenerateBlock(byte *output, size_t size, unsigned int safety)
 		else
 		{
 			if (!safety--)
+			{
+				assert(0);
 				return 0;
+			}
 		}
     }
 		
@@ -275,7 +281,10 @@ static int GCC_RRA_GenerateBlock(byte *output, size_t size, unsigned int safety)
         else
         {
 			if (!safety--)
-				break;
+			{
+				assert(0);
+				return 0;
+			}
         }
 	}
 
@@ -368,7 +377,10 @@ static int ALL_RSI_GenerateBlock(byte *output, size_t size, unsigned int safety)
         else
         {
 			if (!safety--)
+			{
+				assert(0);
 				return 0;
+			}
         }
 	}
 
@@ -386,7 +398,10 @@ static int ALL_RSI_GenerateBlock(byte *output, size_t size, unsigned int safety)
 		else
 		{
 			if (!safety--)
+			{
+				assert(0);
 				return 0;
+			}
 		}
     }
 		
@@ -447,7 +462,10 @@ static int GCC_RSA_GenerateBlock(byte *output, size_t size, unsigned int safety)
         else
         {
 			if (!safety--)
-				break;
+			{
+				assert(0);
+				return 0;
+			}
         }
 	}
 
diff --git a/rdrand.h b/rdrand.h
index fc2b77b7..6f4901be 100644
--- a/rdrand.h
+++ b/rdrand.h
@@ -1,8 +1,7 @@
 // rdrand.h - written and placed in public domain by Jeffrey Walton and Uri Blumenthal.
 //            Copyright assigned to Crypto++ project.
 
-//! \file
-//! \headerfile rdrand.h
+//! \file rdrand.h
 //! \brief Classes for RDRAND and RDSEED
 
 #ifndef CRYPTOPP_RDRAND_H
@@ -15,8 +14,8 @@
 //   indirectly uses CRYPTOPP_BOOL_{X86|X32|X64} (via CRYPTOPP_CPUID_AVAILABLE)
 //   to select an implementation or "throw NotImplemented". At runtime, the
 //   class uses the result of CPUID to determine if RDRAND or RDSEED are
-//   available. A lazy throw strategy is used in case the CPU does not support
-//   the instruction. I.e., the throw is deferred until GenerateBlock() is called.
+//   available. If not available, a lazy throw strategy is used. I.e., the
+//   throw is deferred until GenerateBlock() is called.
 
 // Microsoft added RDRAND in August 2012, VS2012. GCC added RDRAND in December 2010, GCC 4.6.
 // Clang added RDRAND in July 2012, Clang 3.2. Intel added RDRAND in September 2011, ICC 12.1.
@@ -43,7 +42,10 @@ public:
 	//! \param retries the number of retries for failed calls to the hardware
 	//! \details RDRAND() constructs a generator with a maximum number of retires
 	//!   for failed generation attempts.
-	RDRAND(unsigned int retries = 8) : m_retries(retries) {}
+	//! \details Empirical testing under a 6th generaton i7 (6200U) shows RDSEED fails
+	//!   to fulfill requests at about 6 to 8 times the rate of RDRAND. The default
+	//!   retries reflects the difference.
+	RDRAND(unsigned int retries = 12) : m_retries(retries) {}
 	
 	virtual ~RDRAND() {}
 	
@@ -122,7 +124,10 @@ public:
 	//! \param retries the number of retries for failed calls to the hardware
 	//! \details RDSEED() constructs a generator with a maximum number of retires
 	//!   for failed generation attempts.
-	RDSEED(unsigned int retries = 8) : m_retries(retries) {}
+	//! \details Empirical testing under a 6th generaton i7 (6200U) shows RDSEED fails
+	//!   to fulfill requests at about 6 to 8 times the rate of RDRAND. The default
+	//!   retries reflects the difference.
+	RDSEED(unsigned int retries = 64) : m_retries(retries) {}
 	
 	virtual ~RDSEED() {}