From 6ac6668b297654b7a3199a7417b20531dfd9d502 Mon Sep 17 00:00:00 2001
From: Jeffrey Walton <noloader@gmail.com>
Date: Sun, 25 Jun 2023 02:48:20 -0400
Subject: [PATCH] Remove unneeded check in Integer::Randomize(bitCount) (GH
 #1206) Update docs to specify case when bitCount==0 Add tests for Randomize
 function in debug builds

---
 integer.cpp  |  8 ++++++--
 integer.h    |  1 +
 validat2.cpp | 42 +++++++++++++++++++++++++++++++++++++++++-
 3 files changed, 48 insertions(+), 3 deletions(-)

diff --git a/integer.cpp b/integer.cpp
index 81e37b087..5d9043f0f 100644
--- a/integer.cpp
+++ b/integer.cpp
@@ -3522,8 +3522,12 @@ void Integer::Randomize(RandomNumberGenerator &rng, size_t nbits)
 	const size_t nbytes = nbits/8 + 1;
 	SecByteBlock buf(nbytes);
 	rng.GenerateBlock(buf, nbytes);
-	if (nbytes)
-		buf[0] = (byte)Crop(buf[0], nbits % 8);
+
+	// https://github.com/weidai11/cryptopp/issues/1206
+	// if (nbytes)
+	//     buf[0] = (byte)Crop(buf[0], nbits % 8);
+
+	buf[0] = (byte)Crop(buf[0], nbits % 8);
 	Decode(buf, nbytes, UNSIGNED);
 }
 
diff --git a/integer.h b/integer.h
index 4db6b9c37..541cee1c4 100644
--- a/integer.h
+++ b/integer.h
@@ -444,6 +444,7 @@ class CRYPTOPP_DLL Integer : private InitializeInteger, public ASN1Object
 		/// \param rng RandomNumberGenerator used to generate material
 		/// \param bitCount the number of bits in the resulting integer
 		/// \details The random integer created is uniformly distributed over <tt>[0, 2<sup>bitCount</sup>]</tt>.
+		/// \note If \p bitCount is 0, then this Integer is set to 0 (and not 0 or 1).
 		void Randomize(RandomNumberGenerator &rng, size_t bitCount);
 
 		/// \brief Set this Integer to random integer
diff --git a/validat2.cpp b/validat2.cpp
index 5a3be458e..14089fffa 100644
--- a/validat2.cpp
+++ b/validat2.cpp
@@ -1280,7 +1280,47 @@ bool TestIntegerOps()
        std::cout << "FAILED:";
     std::cout << "  Exponentiation operations\n";
 
-    return pass;
+    // ****************************** Integer Randomize ******************************
+
+	try
+	{
+		const word32 bitCounts[] = {
+            0,1,2,3,4,5,6,7,8,9,15,16,17,31,32,33,63,64,65,127,128,129
+		};
+
+		for (size_t i=0; i<COUNTOF(bitCounts); ++i)
+		{
+			result = true;
+            unsigned int maxBits = 0;
+			const size_t bitCount = bitCounts[i];
+			Integer n;
+
+			for (size_t j=0; j<128; ++j)
+			{
+				n.Randomize(prng, bitCount);
+				maxBits = (std::max)(maxBits, n.BitCount());
+			}
+
+			result &= (maxBits == bitCount);
+			if (!result)
+				std::cout << "FAILED:  Randomize " << bitCount << "-bits\n";
+
+			pass &= result;
+		}
+	}
+	catch (const Exception&)
+	{
+		pass = false;
+		result = false;
+	}
+
+	if (!pass)
+		std::cout << "FAILED:";
+	else
+		std::cout << "passed:";
+	std::cout << "  Randomize of various bit lengths\n";
+
+	return pass;
 }
 #endif