diff --git a/chain/src/pipe.rs b/chain/src/pipe.rs
index c040b203e..89900dfd0 100644
--- a/chain/src/pipe.rs
+++ b/chain/src/pipe.rs
@@ -45,11 +45,15 @@ pub struct BlockContext<'a> {
 pub enum Error {
 	/// The block doesn't fit anywhere in our chain
 	Unfit(String),
+	/// Target is too high either compared to ours or the block PoW hash
+	TargetTooHigh,
 	/// The proof of work is invalid
 	InvalidPow,
 	/// The block doesn't sum correctly or a tx signature is invalid
 	InvalidBlockProof(secp::Error),
-	/// Internal issue when trying to save the block
+	/// Block time is too old
+	InvalidBlockTime,
+	/// Internal issue when trying to save or load data from store
 	StoreErr(types::Error),
 }
 
@@ -57,7 +61,7 @@ pub fn process_block(b: &Block, store: &ChainStore, opts: Options) -> Result<(),
 	// TODO should just take a promise for a block with a full header so we don't
 	// spend resources reading the full block when its header is invalid
 
-  let head = try!(store.head().map_err(&Error::StoreErr));
+	let head = try!(store.head().map_err(&Error::StoreErr));
 	let mut ctx = BlockContext {
 		opts: opts,
 		store: store,
@@ -92,19 +96,30 @@ fn validate_header(b: &Block, ctx: &mut BlockContext) -> Result<(), Error> {
 		// TODO actually handle orphans and add them to a size-limited set
 		return Err(Error::Unfit("orphan".to_string()));
 	}
-	// TODO check time wrt to chain time, refuse older than 100 blocks or too far
-	// in future
+	// TODO check time wrt to chain time, refuse too far in future
 
-	// TODO maintain current difficulty
-	let diff_target = consensus::MAX_TARGET;
+	let prev = try!(ctx.store.get_block_header(&header.previous).map_err(&Error::StoreErr));
+
+	if header.timestamp <= prev.timestamp {
+		return Err(Error::InvalidBlockTime);
+	}
+
+	let (diff_target, cuckoo_sz) = consensus::next_target(header.timestamp.to_timespec().sec,
+	                                                      prev.timestamp.to_timespec().sec,
+	                                                      prev.target,
+	                                                      prev.cuckoo_len);
+	if header.target > diff_target {
+		return Err(Error::TargetTooHigh);
+	}
 
 	if ctx.opts.intersects(EASY_POW) {
-		if !pow::verify20(b, diff_target) {
+		if !pow::verify20(b) {
 			return Err(Error::InvalidPow);
 		}
-	} else if !pow::verify(b, diff_target) {
+	} else if !pow::verify_size(b, cuckoo_sz as u32) {
 		return Err(Error::InvalidPow);
 	}
+
 	Ok(())
 }
 
diff --git a/chain/src/store.rs b/chain/src/store.rs
index 594d2b275..9bc1a2da1 100644
--- a/chain/src/store.rs
+++ b/chain/src/store.rs
@@ -17,14 +17,16 @@
 use byteorder::{WriteBytesExt, BigEndian};
 
 use types::*;
-use core::core::Block;
+use core::core::hash::Hash;
+use core::core::{Block, BlockHeader};
 use grin_store;
 
 const STORE_PATH: &'static str = ".grin/chain";
 
 const SEP: u8 = ':' as u8;
 
-const BLOCK_PREFIX: u8 = 'B' as u8;
+const BLOCK_HEADER_PREFIX: u8 = 'h' as u8;
+const BLOCK_PREFIX: u8 = 'b' as u8;
 const TIP_PREFIX: u8 = 'T' as u8;
 const HEAD_PREFIX: u8 = 'H' as u8;
 
@@ -47,7 +49,17 @@ impl ChainStore for ChainKVStore {
 	}
 
 	fn save_block(&self, b: &Block) -> Result<(), Error> {
-		self.db.put_ser(&to_key(BLOCK_PREFIX, &mut b.hash().to_vec())[..], b).map_err(&to_store_err)
+		try!(self.db
+			.put_ser(&to_key(BLOCK_PREFIX, &mut b.hash().to_vec())[..], b)
+			.map_err(&to_store_err));
+		self.db
+			.put_ser(&to_key(BLOCK_HEADER_PREFIX, &mut b.hash().to_vec())[..],
+			         &b.header)
+			.map_err(&to_store_err)
+	}
+
+	fn get_block_header(&self, h: &Hash) -> Result<BlockHeader, Error> {
+		option_to_not_found(self.db.get_ser(&to_key(BLOCK_HEADER_PREFIX, &mut h.to_vec())))
 	}
 
 	fn save_head(&self, t: &Tip) -> Result<(), Error> {
diff --git a/chain/src/types.rs b/chain/src/types.rs
index 185742554..9acbeff2d 100644
--- a/chain/src/types.rs
+++ b/chain/src/types.rs
@@ -15,7 +15,7 @@
 //! Base types that the block chain pipeline requires.
 
 use core::core::hash::Hash;
-use core::core::Block;
+use core::core::{Block, BlockHeader};
 use core::ser;
 
 /// The lineage of a fork, defined as a series of numbers. Each new branch gets
@@ -137,6 +137,9 @@ pub trait ChainStore {
 	/// Get the tip that's also the head of the chain
 	fn head(&self) -> Result<Tip, Error>;
 
+	/// Gets a block header by hash
+	fn get_block_header(&self, h: &Hash) -> Result<BlockHeader, Error>;
+
 	/// Save the provided block in store
 	fn save_block(&self, b: &Block) -> Result<(), Error>;
 
diff --git a/store/src/lib.rs b/store/src/lib.rs
index beb793c5f..61d952e06 100644
--- a/store/src/lib.rs
+++ b/store/src/lib.rs
@@ -87,10 +87,16 @@ impl Store {
 	/// Gets a `Readable` value from the db, provided its key. Encapsulates
 	/// serialization.
 	pub fn get_ser<T: ser::Readable<T>>(&self, key: &[u8]) -> Result<Option<T>, Error> {
+    self.get_ser_limited(key, 0)
+	}
+
+	/// Gets a `Readable` value from the db, provided its key, allowing to extract only partial data. The underlying Readable size must align accordingly. Encapsulates serialization.
+	pub fn get_ser_limited<T: ser::Readable<T>>(&self, key: &[u8], len: usize) -> Result<Option<T>, Error> {
 		let data = try!(self.get(key));
 		match data {
 			Some(val) => {
-				let r = try!(ser::deserialize(&mut &val[..]).map_err(Error::SerErr));
+        let mut lval = if len > 0 { &val[..len] } else { &val[..] };
+				let r = try!(ser::deserialize(&mut lval).map_err(Error::SerErr));
 				Ok(Some(r))
 			}
 			None => Ok(None),