diff --git a/src/cpp/ripple/ProofOfWork.cpp b/src/cpp/ripple/ProofOfWork.cpp
index 9ccb29eb25..7d1df26567 100644
--- a/src/cpp/ripple/ProofOfWork.cpp
+++ b/src/cpp/ripple/ProofOfWork.cpp
@@ -2,9 +2,14 @@
 
 #include <string>
 
+#include <boost/test/unit_test.hpp>
+
 #include <openssl/rand.h>
 
 #include "Serializer.h"
+#include "Log.h"
+
+SETUP_LOG();
 
 const uint256 ProofOfWork::sMinTarget("00000000FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF");
 const int ProofOfWork::sMaxIterations(1 << 23);
@@ -16,26 +21,38 @@ bool ProofOfWork::isValid() const
 
 uint64 ProofOfWork::getDifficulty(const uint256& target, int iterations)
 { // calculate the approximate number of hashes required to solve this proof of work
-	if ((iterations > sMaxIterations) || (target < sMinTarget));
+	if ((iterations > sMaxIterations) || (target < sMinTarget))
+	{
+		cLog(lsINFO) << "Iterations:" << iterations;
+		cLog(lsINFO) << "MaxIterat: " << sMaxIterations;
+		cLog(lsINFO) << "Target:    " << target;
+		cLog(lsINFO) << "MinTarget: " << sMinTarget;
 		throw std::runtime_error("invalid proof of work target/iteration");
+	}
 
 	// more iterations means more hashes per iteration but also a larger final hash
 	uint64 difficulty = iterations * (iterations / 4 + 1);
 
-	// Multiply the number of hashes needed by 16 for each leading zero in the hex difficulty
-	const unsigned char *ptr = target.begin();
+	// Multiply the number of hashes needed by 256 for each leading zero byte in the hex difficulty
+	const unsigned char *ptr = target.end() - 1;
 	while (*ptr == 0)
 	{
-		difficulty *= 16;
-		ptr++;
+		cLog(lsINFO) << "getDif: " << (int) *ptr;
+		difficulty *= 256;
+		--ptr;
 	}
 
 	// If the first digit after a zero isn't an F, multiply
-	difficulty *= (16 - *ptr);
+	difficulty *= (256 - *ptr);
 
 	return difficulty;
 }
 
+static uint256 getSHA512Half(const std::vector<uint256>& vec)
+{
+	return Serializer::getSHA512Half(vec.front().begin(), vec.size() * (256 / 8));
+}
+
 uint256 ProofOfWork::solve(int maxIterations) const
 {
 	if (!isValid())
@@ -44,23 +61,49 @@ uint256 ProofOfWork::solve(int maxIterations) const
 	uint256 nonce;
 	RAND_bytes(nonce.begin(), nonce.size());
 
-	Serializer s1, s2;
-	std::vector<unsigned char> buf;
-	buf.reserve((256 / 8) * mIterations);
+	std::vector<uint256> buf2;
+	buf2.resize(mIterations);
 
-	while (maxIterations > 8)
+	std::vector<uint256> buf1;
+	buf1.resize(3);
+	buf1[0] = mChallenge;
+
+	while (maxIterations > 0)
 	{
-		s1.add256(mChallenge);
-		s1.add256(nonce);
-//		uint256 base = s1.getSHA512Half();
-
-		for (int i = 0; i < mIterations; ++i)
+		buf1[1] = nonce;
+		buf1[2] = uint256();
+		for (int i = (mIterations - 1); i >= 0; --i)
 		{
-			// WRITEME
+			if (buf1.size() != 3)
+				Log(lsINFO) << "buf1.size=" << buf1.size();
+			buf1[2] = getSHA512Half(buf1);
+			buf2[i] = buf1[2];
 		}
+		if (buf2.size() != mIterations)
+			Log(lsINFO) << "buf2.size=" << buf2.size();
 
-		s1.erase();
-		nonce++;
+		uint256 hash = getSHA512Half(buf2);
+		if (hash <= mTarget)
+			return nonce;
+
+		++nonce;
+		--maxIterations;
 	}
 	return uint256();
 }
+
+BOOST_AUTO_TEST_SUITE(ProofOfWork_suite)
+
+BOOST_AUTO_TEST_CASE( ProofOfWork_test )
+{
+	ProofOfWork pow("test", 32, uint256(),
+		uint256("00FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF"));
+	cLog(lsINFO) << "Estimated difficulty: " << pow.getDifficulty();
+	uint256 solution = pow.solve(16777216);
+	if (solution.isZero())
+		BOOST_FAIL("Unable to solve proof of work");
+}
+
+BOOST_AUTO_TEST_SUITE_END()
+
+// vim:ts=4
diff --git a/src/cpp/ripple/ProofOfWork.h b/src/cpp/ripple/ProofOfWork.h
index 1391be91c3..6540b07130 100644
--- a/src/cpp/ripple/ProofOfWork.h
+++ b/src/cpp/ripple/ProofOfWork.h
@@ -10,6 +10,15 @@
 
 #include "uint256.h"
 
+enum POWResult
+{
+	powOK		= 0,
+	powREUSED	= 1,
+	powBADNONCE	= 2,
+	powBADTOKEN	= 3,
+	powEXPIRED	= 4,
+};
+
 class ProofOfWork
 {
 protected:
@@ -48,6 +57,7 @@ protected:
 	int								mIterations;
 	uint256							mTarget;
 	time_t							mLastDifficultyChange;
+	int								mValidTime;
 
 	powMap_t						mSolvedChallenges;
 	boost::mutex					mLock;
@@ -64,3 +74,5 @@ public:
 };
 
 #endif
+
+// vim:ts=4
diff --git a/src/cpp/ripple/uint256.h b/src/cpp/ripple/uint256.h
index 3e2ab10e62..e7e5e449ee 100644
--- a/src/cpp/ripple/uint256.h
+++ b/src/cpp/ripple/uint256.h
@@ -23,7 +23,7 @@
 #endif
 
 // These classes all store their values internally
-// in little-endian form
+// in big-endian form
 
 inline int Testuint256AdHoc(std::vector<std::string> vArg);
 
@@ -36,7 +36,7 @@ protected:
 	enum { WIDTH=BITS/32 };
 
 	// This is really big-endian in byte order.
-	// We use unsigned int for speed.
+	// We sometimes use unsigned int for speed.
 	unsigned int pn[WIDTH];
 
 public:
@@ -73,7 +73,7 @@ public:
 		zero();
 
 		// Put in least significant bits.
-		((uint64_t *) end())[-1]	= htobe64(uHost);
+		((uint64_t *) end())[-1] = htobe64(uHost);
 
 		return *this;
 	}
@@ -105,10 +105,12 @@ public:
 	base_uint& operator++()
 	{
 		// prefix operator
-		int		i = WIDTH;
-
-		while (i-- && !++pn[i])
-			;
+		for (int i = WIDTH - 1; i >= 0; --i)
+		{
+			pn[i] = htobe32(be32toh(pn[i]) + 1);
+			if (pn[i] != 0)
+				break;
+		}
 
 		return *this;
 	}
@@ -124,10 +126,13 @@ public:
 
 	base_uint& operator--()
 	{
-		int		i = WIDTH;
-
-		while (i-- && !pn[i]--)
-			;
+		for (int i = WIDTH - 1; i >= 0; --i)
+		{
+			uint32 prev = pn[i];
+			pn[i] = htobe32(be32toh(pn[i]) - 1);
+			if (prev != 0)
+				break;
+		}
 
 		return *this;
 	}
@@ -169,10 +174,14 @@ public:
 		const unsigned char* pAEnd	= a.end();
 		const unsigned char* pB		= b.begin();
 
-		while (pA != pAEnd && *pA == *pB)
-			pA++, pB++;
+		while (*pA == *pB)
+		{
+			if (++pA == pAEnd)
+				return 0;
+			++pB;
+		}
 
-		return pA == pAEnd ? 0 : *pA < *pB ? -1 : *pA > *pB ? 1 : 0;
+		return (*pA < *pB) ? -1 : 1;
 	}
 
 	friend inline bool operator<(const base_uint& a, const base_uint& b)