diff --git a/src/crypto.rs b/src/crypto.rs
index 9a27c68ae..35bb3b7eb 100644
--- a/src/crypto.rs
+++ b/src/crypto.rs
@@ -120,6 +120,8 @@ impl KeyPair {
 
 pub mod ec {
 	use hash::*;
+	use uint::*;
+	use standard::*;
 	use crypto::*;
 	use crypto::{self};
 
@@ -136,6 +138,7 @@ pub mod ec {
 	}
 	/// Returns siganture of message hash.
 	pub fn sign(secret: &Secret, message: &H256) -> Result<Signature, CryptoError> {
+		// TODO: allow creation of only low-s signatures.
 		use secp256k1::*;
 		let context = Secp256k1::new();
 		let sec: &key::SecretKey = unsafe { ::std::mem::transmute(secret) };
@@ -165,6 +168,16 @@ pub mod ec {
 		}
 	}
 
+	/// Check if this is a "low" signature.
+	pub fn is_low(sig: &Signature) -> bool {
+		H256::from_slice(&sig[32..64]) <= h256_from_hex("7FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF5D576E7357A4501DDFE92F46681B20A0")
+	}
+
+	/// Check if this is a "low" signature.
+	pub fn is_low_s(s: &U256) -> bool {
+		s <= &U256::from_str("7FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF5D576E7357A4501DDFE92F46681B20A0").unwrap()
+	}
+
 	/// Check if each component of the signature is in range.
 	pub fn is_valid(sig: &Signature) -> bool {
 		sig[64] <= 1 &&
diff --git a/src/hash.rs b/src/hash.rs
index 087454ceb..5eb76a05e 100644
--- a/src/hash.rs
+++ b/src/hash.rs
@@ -224,16 +224,22 @@ macro_rules! impl_hash {
 			}
 		}
 
-		impl PartialOrd for $from {
-			fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
+		impl Ord for $from {
+			fn cmp(&self, other: &Self) -> Ordering {
 				for i in 0..$size {
 					if self.0[i] > other.0[i] {
-						return Some(Ordering::Greater);
+						return Ordering::Greater;
 					} else if self.0[i] < other.0[i] {
-						return Some(Ordering::Less);
+						return Ordering::Less;
 					}
 				}
-				Some(Ordering::Equal)
+				Ordering::Equal
+			}
+		}
+
+		impl PartialOrd for $from {
+			fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
+				Some(self.cmp(other))
 			}
 		}
 
diff --git a/src/json_aid.rs b/src/json_aid.rs
new file mode 100644
index 000000000..a382c61ec
--- /dev/null
+++ b/src/json_aid.rs
@@ -0,0 +1,68 @@
+use common::*;
+
+pub fn clean(s: &str) -> &str {
+	if s.len() >= 2 && &s[0..2] == "0x" {
+		&s[2..]
+	} else {
+		s
+	}
+}
+
+pub fn bytes_from_json(json: &Json) -> Bytes {
+	let s = json.as_string().unwrap_or("");
+	if s.len() % 2 == 1 {
+		FromHex::from_hex(&("0".to_string() + &(clean(s).to_string()))[..]).unwrap_or(vec![])
+	} else {
+		FromHex::from_hex(clean(s)).unwrap_or(vec![])
+	}
+}
+
+pub fn address_from_json(json: &Json) -> Address {
+	let s = json.as_string().unwrap_or("0000000000000000000000000000000000000000");
+	if s.len() % 2 == 1 {
+		address_from_hex(&("0".to_string() + &(clean(s).to_string()))[..])
+	} else {
+		address_from_hex(clean(s))
+	}
+}
+
+pub fn h256_from_json(json: &Json) -> H256 {
+	let s = json.as_string().unwrap_or("0000000000000000000000000000000000000000000000000000000000000000");
+	if s.len() % 2 == 1 {
+		h256_from_hex(&("0".to_string() + &(clean(s).to_string()))[..])
+	} else {
+		h256_from_hex(clean(s))
+	}
+}
+
+pub fn u256_from_hex(s: &str) -> U256 {
+	if s.len() >= 2 && &s[0..2] == "0x" {
+		U256::from_str(&s[2..]).unwrap_or(U256::from(0))
+	} else {
+		U256::from_dec_str(s).unwrap_or(U256::from(0))
+	}
+}
+
+pub fn u256_from_json(json: &Json) -> U256 {
+	u256_from_hex(json.as_string().unwrap_or(""))
+}
+
+pub fn usize_from_json(json: &Json) -> usize {
+	u256_from_json(json).low_u64() as usize
+}
+
+pub fn u64_from_json(json: &Json) -> u64 {
+	u256_from_json(json).low_u64()
+}
+
+pub fn u32_from_json(json: &Json) -> u32 {
+	u256_from_json(json).low_u32()
+}
+
+pub fn u16_from_json(json: &Json) -> u16 {
+	u256_from_json(json).low_u32() as u16
+}
+
+pub fn u8_from_json(json: &Json) -> u8 {
+	u256_from_json(json).low_u32() as u8
+}
diff --git a/src/lib.rs b/src/lib.rs
index b856431cd..7bfe147f9 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -57,6 +57,7 @@ pub mod hash;
 pub mod uint;
 pub mod bytes;
 pub mod rlp;
+pub mod json_aid;
 pub mod vector;
 pub mod sha3;
 pub mod hashdb;
@@ -74,6 +75,7 @@ pub mod semantic_version;
 pub mod network;
 
 pub use common::*;
+pub use json_aid::*;
 pub use rlp::*;
 pub use hashdb::*;
 pub use memorydb::*;
diff --git a/src/rlp/rlperrors.rs b/src/rlp/rlperrors.rs
index 27b3082b5..9ea470abf 100644
--- a/src/rlp/rlperrors.rs
+++ b/src/rlp/rlperrors.rs
@@ -9,6 +9,9 @@ pub enum DecoderError {
 	RlpExpectedToBeList,
 	RlpExpectedToBeData,
 	RlpIncorrectListLen,
+	RlpDataLenWithZeroPrefix,
+	RlpListLenWithZeroPrefix,
+	RlpInvalidIndirection,
 }
 
 impl StdError for DecoderError {
diff --git a/src/rlp/untrusted_rlp.rs b/src/rlp/untrusted_rlp.rs
index 452a198bb..c0e7c4cf7 100644
--- a/src/rlp/untrusted_rlp.rs
+++ b/src/rlp/untrusted_rlp.rs
@@ -269,6 +269,7 @@ impl<'a> BasicDecoder<'a> {
 			Some(l @ 0xb8...0xbf) => {
 				let len_of_len = l as usize - 0xb7;
 				let header_len = 1 + len_of_len;
+				if bytes[1] == 0 { return Err(DecoderError::RlpDataLenWithZeroPrefix); }
 				let value_len = try!(usize::from_bytes(&bytes[1..header_len]));
 				PayloadInfo::new(header_len, value_len)
 			}
@@ -277,6 +278,7 @@ impl<'a> BasicDecoder<'a> {
 				let len_of_len = l as usize - 0xf7;
 				let header_len = 1 + len_of_len;
 				let value_len = try!(usize::from_bytes(&bytes[1..header_len]));
+				if bytes[1] == 0 { return Err(DecoderError::RlpListLenWithZeroPrefix); }
 				PayloadInfo::new(header_len, value_len)
 			},
 			// we cant reach this place, but rust requires _ to be implemented
@@ -302,7 +304,13 @@ impl<'a> Decoder for BasicDecoder<'a> {
 			// single byt value
 			Some(l @ 0...0x7f) => Ok(try!(f(&[l]))),
 			// 0-55 bytes
-			Some(l @ 0x80...0xb7) => Ok(try!(f(&bytes[1..(1 + l as usize - 0x80)]))),
+			Some(l @ 0x80...0xb7) => {
+				let d = &bytes[1..(1 + l as usize - 0x80)];
+				if l == 0x81 && d[0] < 0x80 {
+					return Err(DecoderError::RlpInvalidIndirection);
+				}
+				Ok(try!(f(d)))
+			},
 			// longer than 55 bytes
 			Some(l @ 0xb8...0xbf) => {
 				let len_of_len = l as usize - 0xb7;