diff --git a/blockchain.py b/blockchain.py
index 04fc6e1..e13c0fc 100644
--- a/blockchain.py
+++ b/blockchain.py
@@ -2,6 +2,7 @@ from dataclasses import dataclass
 from cryptography.hazmat.primitives.asymmetric.ed25519 import Ed25519PrivateKey, Ed25519PublicKey
 from cryptography.exceptions import InvalidSignature
 import hashlib
+from multiprocessing import Lock
 import time
 
 @dataclass
@@ -13,6 +14,16 @@ class Transaction:
     transaction_fee: int
     signature: bytes
 
+    def from_bytes(transaction_raw):
+        assert len(transaction_raw) == 148
+        return Transaction(
+            id: int.from_bytes(transaction_raw[0:4], "big"),
+            sender: transaction_raw[4:36],
+            receiver: transaction_raw[36:68],
+            amount: int.from_bytes(transaction_raw[68:76], "big"),
+            transaction_fee: int.from_bytes(transaction_raw[76:84], "big"),
+            signature: transaction_raw[84:148],
+        )
     def is_valid(self):
         sender_pubkey = Ed25519PublicKey.from_public_bytes(self.sender)
         msg = self.id.to_bytes(4, "big") + \
@@ -49,11 +60,32 @@ class Block:
     difficulty_sum: int
     miner_pubkey: bytes
     transaction: Transaction
+    own_hash: bytes
     balances: dict
     # (sender_pubkey, id) tuples
     used_transaction_ids: set
     valid: bool
 
+    def from_bytes(self, block_raw):
+        assert len(block_raw) == 292
+        transaction_raw = block_raw[144:292]
+        if transaction_raw == 148 * b"\0":
+            transaction = None
+        else:
+            transaction = Transaction.from_bytes(transaction_raw)
+        block = Block(
+            nonce: int.from_bytes(block_raw[0:8], "big"),
+            timestamp: int.from_bytes(block_raw[8:16], "big"),
+            previous_hash: block_raw[16:48],
+            message: block_raw[48:80],
+            difficulty_sum: int.from_bytes(block_raw[80:112], "big"),
+            miner_pubkey: block_raw[112:144],
+            transaction: transaction,
+            own_hash: hashlib.sha256(block_raw).digest(),
+            balances: None,
+            used_transaction_ids: None,
+            valid: False,
+        )
     def validate(self, blockchain):
         if self.transaction is not None:
             if not self.transaction.is_valid():
@@ -83,9 +115,7 @@ class Block:
         block_difficulty = max(calculated_difficulty, 2**28)
         if B_1_difficulty_sum + block_difficulty != self.difficulty_sum:
             return False
-        block_raw = self.get_block_raw()
-        block_hash = hashlib.sha256(block_raw).digest()
-        self.valid = int.from_bytes(block_hash, "big") * block_difficulty < 2**256
+        self.valid = int.from_bytes(self.own_hash, "big") * block_difficulty < 2**256
         if self.valid:
             self.calculate_balances(prev_block)
             self.calculate_used_transaction_ids(prev_block)
@@ -141,5 +171,24 @@ class Blockchain:
     def __init__(self):
         # maps block hashes to block instances
         self.__block_map = {}
+        self.__latest_block_hash = None
+        self.__lock = Lock()
+    def set_latest_block(self, block_hash):
+        with self.__lock:
+            new_block = self.get_block(block_hash)
+            assert new_block is not None
+            assert new_block.valid
+            if self.__latest_block_hash is not None:
+                current_difficulty_sum = self.__latest_block_hash.get_difficulty_info(1, self)
+                new_difficulty_sum = new_block.get_difficulty_info(1, self)
+                if new_difficulty_sum <= current_difficulty_sum:
+                    return
+            self.__latest_block_hash = block_hash
+    def add_block(self, block_raw):
+        with self.__lock:
+            block = Block.from_bytes(block_raw)
+            self.__block_map[block.own_hash] = block
+            return block
     def get_block(self, hash):
-        return self.__block_map.get(hash)
+        with self.__lock:
+            return self.__block_map.get(hash)