section 3.3 added

script/research/streamlet/2-execution-model-and-definitions.py

@@ -13,7 +13,7 @@ class Node:
 		self.inputs = []
 	
 	def __repr__(self):
-		return "Node=[id={0}, secret_key={1}, public_key={2}]".format(self.id, self.secret_key, self.public_key)
+		return "Node=[id={0}, secret_key={1}, public_key={2}, blockchain={3}, inputs={4}".format(self.id, self.secret_key, self.public_key, self.blockchain, self.inputs)
 		
 	def receive_input(self, input):
 		# Additional validity rules must be defined by the protocol for its blockchain data structure.

script/research/streamlet/3.3-votes-and-notarization.py

@@ -0,0 +1,62 @@
+# Section 3.3 from "Streamlet: Textbook Streamlined Blockchains"
+
+from cryptography.hazmat.primitives import serialization, hashes
+from cryptography.hazmat.primitives.asymmetric import rsa, padding
+from cryptography.hazmat.backends import default_backend
+from cryptography.exceptions import InvalidSignature
+
+# Cryptographic algorithm used is for demostranation porpuses only.
+# Generating the keys pair. 
+def generate_keys(private_key_password):
+	private_key = rsa.generate_private_key(
+		public_exponent=65537,
+		key_size=2048
+	)	
+	encrypted_pem_private_key = private_key.private_bytes(
+		encoding=serialization.Encoding.PEM,
+		format=serialization.PrivateFormat.PKCS8,
+		encryption_algorithm=serialization.BestAvailableEncryption(private_key_password.encode())
+	)
+	pem_public_key = private_key.public_key().public_bytes(
+	  encoding=serialization.Encoding.PEM,
+	  format=serialization.PublicFormat.SubjectPublicKeyInfo
+	)
+	
+	return encrypted_pem_private_key, pem_public_key
+
+# Signs a message using private_key
+def sign_message(password, private_key, message):
+	privkey = serialization.load_pem_private_key(private_key, password=password.encode(), backend=default_backend())
+	signed_message = privkey.sign(
+		message.encode(),
+		padding.PSS(
+			mgf=padding.MGF1(hashes.SHA256()),
+			salt_length=padding.PSS.MAX_LENGTH),
+		hashes.SHA256()
+	)
+	return signed_message
+	
+# Verifies a message against a public key
+def verify_signature(public_key, message, signed_message):
+	pubkey = serialization.load_pem_public_key(public_key, backend=default_backend())
+	try:
+		pubkey.verify(
+			signed_message,
+			message.encode(),
+			padding.PSS(
+				mgf=padding.MGF1(hashes.SHA256()),
+				salt_length=padding.PSS.MAX_LENGTH),
+			hashes.SHA256())
+		return True
+	except InvalidSignature:
+		return False
+
+# When a node votes on a block, it simply signs it with the private key, and broadcasts the message to rest nodes.	
+message = "block"
+node_password = "node_password"	
+node_private_key, node_public_key = generate_keys(node_password)
+signed_message = sign_message(node_password, node_private_key, message)
+
+# When nodes receive votes, they verify them against nodes public key.
+assert(verify_signature(node_public_key, message, signed_message))
+# If votes for that specific block are >=2n/3, node marks block as notarized