diff --git a/libethereum/BlockInfo.cpp b/libethereum/BlockInfo.cpp
index a1a9781d1..1ebc5eb58 100644
--- a/libethereum/BlockInfo.cpp
+++ b/libethereum/BlockInfo.cpp
@@ -36,13 +36,13 @@ void BlockInfo::populateAndVerify(bytesConstRef _block, u256 _number)
 	{
 		RLP header = root[0];
 		hash = eth::sha256(_block);
-		parentHash = header[0].toFatInt();
-		sha256Uncles = header[1].toFatInt();
-		coinbaseAddress = header[2].toFatInt();
-		sha256Transactions = header[3].toFatInt();
-		difficulty = header[4].toFatInt();
-		timestamp = header[5].toFatInt();
-		nonce = header[6].toFatInt();
+		parentHash = header[0].toInt<u256>();
+		sha256Uncles = header[1].toInt<u256>();
+		coinbaseAddress = header[2].toInt<u160>();
+		sha256Transactions = header[3].toInt<u256>();
+		difficulty = header[4].toInt<uint>();
+		timestamp = header[5].toInt<u256>();
+		nonce = header[6].toInt<u256>();
 	}
 	catch (RLP::BadCast)
 	{
diff --git a/libethereum/RLP.cpp b/libethereum/RLP.cpp
index e56b68c50..7cf0dd41c 100644
--- a/libethereum/RLP.cpp
+++ b/libethereum/RLP.cpp
@@ -191,7 +191,7 @@ std::ostream& operator<<(std::ostream& _out, eth::RLP _d)
 	if (_d.isNull())
 		_out << "null";
 	else if (_d.isInt())
-		_out << std::showbase << std::hex << std::nouppercase << _d.toBigInt();
+		_out << std::showbase << std::hex << std::nouppercase << _d.toBigInt(RLP::LaisezFaire);
 	else if (_d.isString())
 		_out << eth::escaped(_d.toString(), true);
 	else if (_d.isList())
diff --git a/libethereum/RLP.h b/libethereum/RLP.h
index b01fbccdc..5d103b5fb 100644
--- a/libethereum/RLP.h
+++ b/libethereum/RLP.h
@@ -35,6 +35,11 @@ namespace eth
 class RLP;
 typedef std::vector<RLP> RLPs;
 
+template <class _T> struct intTraits { static const uint maxSize = sizeof(_T); };
+template <> struct intTraits<u160> { static const uint maxSize = 20; };
+template <> struct intTraits<u256> { static const uint maxSize = 32; };
+template <> struct intTraits<bigint> { static const uint maxSize = ~(uint)0; };
+
 /**
  * @brief Class for interpreting Recursive Linear-Prefix Data.
  * @by Gav Wood, 2013
@@ -160,15 +165,41 @@ public:
 	/// Converts to string. @throws BadCast if not a string.
 	std::string toStringStrict() const { if (!isString()) throw BadCast(); return payload().cropped(0, items()).toString(); }
 
+	/// Int conversion flags
+	enum
+	{
+		AllowString = 1,
+		AllowInt = 2,
+		ThrowOnFail = 4,
+		FailIfTooBig = 8,
+		Strict = AllowString | AllowInt | ThrowOnFail | FailIfTooBig,
+		StrictlyString = AllowString | ThrowOnFail | FailIfTooBig,
+		StrictlyInt = AllowInt | ThrowOnFail | FailIfTooBig,
+		LaisezFaire = AllowString | AllowInt
+	};
+
 	/// Converts to int of type given; if isString(), decodes as big-endian bytestream. @returns 0 if not an int or string.
-	template <class _T = uint> _T toInt() const
+	template <class _T = uint> _T toInt(int _flags = Strict) const
 	{
-		if (!isString() && !isInt())
-			return 0;
+		if ((isString() && !(_flags & AllowString)) || (isInt() && !(_flags & AllowInt)) || isList() || isNull())
+			if (_flags & ThrowOnFail)
+				throw BadCast();
+			else
+				return 0;
+		else {}
+
 		if (isDirectValueInt())
 			return m_data[0];
-		_T ret = 0;
+
 		auto s = isInt() ? intSize() - lengthSize() : isString() ? items() : 0;
+		if (s > intTraits<_T>::maxSize && (_flags & FailIfTooBig))
+			if (_flags & ThrowOnFail)
+				throw BadCast();
+			else
+				return 0;
+		else {}
+
+		_T ret = 0;
 		uint o = lengthSize() + 1;
 		for (uint i = 0; i < s; ++i)
 			ret = (ret << 8) | m_data[i + o];
@@ -176,25 +207,13 @@ public:
 	}
 
 	/// Converts to eth::uint. @see toInt()
-	uint toSlimInt() const { return toInt<uint>(); }
+	uint toSlimInt(int _flags = Strict) const { return toInt<uint>(_flags); }
+
 	/// Converts to eth::u256. @see toInt()
-	u256 toFatInt() const { return toInt<u256>(); }
+	u256 toFatInt(int _flags = Strict) const { return toInt<u256>(_flags); }
+
 	/// Converts to eth::bigint. @see toInt()
-	bigint toBigInt() const { return toInt<bigint>(); }
-
-	/// Converts to eth::uint. @throws BadCast if not isInt(). @see toInt()
-	uint toSlimIntStrict() const { if (!isSlimInt()) throw BadCast(); return toInt<uint>(); }
-	/// Converts to eth::u256. @throws BadCast if not isInt(). @see toInt()
-	u256 toFatIntStrict() const { if (!isFatInt() && !isSlimInt()) throw BadCast(); return toInt<u256>(); }
-	/// Converts to eth::bigint. @throws BadCast if not isInt(). @see toInt()
-	bigint toBigIntStrict() const { if (!isInt()) throw BadCast(); return toInt<bigint>(); }
-
-	/// Converts to eth::uint using the toString() as a big-endian bytestream. @throws BadCast if not isString(). @see toInt()
-	uint toSlimIntFromString() const { if (!isString()) throw BadCast(); return toInt<uint>(); }
-	/// Converts to eth::u256 using the toString() as a big-endian bytestream. @throws BadCast if not isString(). @see toInt()
-	u256 toFatIntFromString() const { if (!isString()) throw BadCast(); return toInt<u256>(); }
-	/// Converts to eth::bigint using the toString() as a big-endian bytestream. @throws BadCast if not isString(). @see toInt()
-	bigint toBigIntFromString() const { if (!isString()) throw BadCast(); return toInt<bigint>(); }
+	bigint toBigInt(int _flags = Strict) const { return toInt<bigint>(_flags); }
 
 	/// Converts to RLPs collection object. Useful if you need random access to sub items or will iterate over multiple times.
 	RLPs toList() const;
diff --git a/libethereum/State.cpp b/libethereum/State.cpp
index ee93f2cdf..e4f54869b 100644
--- a/libethereum/State.cpp
+++ b/libethereum/State.cpp
@@ -93,8 +93,17 @@ u256 State::contractMemory(Address _contract, u256 _memory) const
 	return i == m->second.memory().end() ? 0 : i->second;
 }
 
-bool State::verify(bytes const& _block)
+bool State::verify(bytes const& _block, uint _number)
 {
+	BlockInfo bi;
+	try
+	{
+		bi.populateAndVerify(bytesConstRef((bytes*)&_block), _number);
+	}
+	catch (...)
+	{
+		return false;
+	}
 	return true;
 }
 
diff --git a/libethereum/State.h b/libethereum/State.h
index 3c9b828ae..2c6cea961 100644
--- a/libethereum/State.h
+++ b/libethereum/State.h
@@ -39,7 +39,7 @@ class State
 public:
 	explicit State(Address _minerAddress);
 
-	bool verify(bytes const& _block);
+	bool verify(bytes const& _block, uint _number = 0);
 	bool execute(bytes const& _rlp) { try { Transaction t(_rlp); execute(t, t.sender()); } catch (...) { return false; } }
 
 	bool isNormalAddress(Address _address) const;
diff --git a/libethereum/Transaction.cpp b/libethereum/Transaction.cpp
index b78ec6ee0..5f30141b2 100644
--- a/libethereum/Transaction.cpp
+++ b/libethereum/Transaction.cpp
@@ -28,14 +28,14 @@ using namespace eth;
 Transaction::Transaction(bytes const& _rlpData)
 {
 	RLP rlp(_rlpData);
-	nonce = rlp[0].toFatIntStrict();
-	receiveAddress = as160(rlp[1].toFatIntFromString());
-	value = rlp[2].toFatIntStrict();
-	fee = rlp[3].toFatIntStrict();
+	nonce = rlp[0].toInt<u256>(RLP::StrictlyInt);
+	receiveAddress = rlp[1].toInt<u160>(RLP::StrictlyString);
+	value = rlp[2].toInt<u256>(RLP::StrictlyInt);
+	fee = rlp[3].toInt<u256>(RLP::StrictlyInt);
 	data.reserve(rlp[4].itemCountStrict());
 	for (auto const& i: rlp[4])
-		data.push_back(i.toFatIntStrict());
-	vrs = Signature{ (byte)rlp[5].toSlimIntStrict(), rlp[6].toFatIntStrict(), rlp[7].toFatIntStrict() };
+		data.push_back(i.toInt<u256>(RLP::StrictlyInt));
+	vrs = Signature{ rlp[5].toInt<byte>(RLP::StrictlyInt), rlp[6].toInt<u256>(RLP::StrictlyInt), rlp[7].toInt<u256>(RLP::StrictlyInt) };
 }
 
 Address Transaction::sender() const