1 files changed, 81 insertions, 0 deletions
diff --git a/flags/rsa.py b/flags/rsa.py
new file mode 100755
index 0000000..96fc947
--- /dev/null
+++ b/flags/rsa.py
@@ -0,0 +1,81 @@
+#!/usr/bin/env python
+
+# Load up the goods.
+with open('rsa.flag', 'r') as f:
+	flag = f.read(32)
+
+from Crypto.PublicKey import RSA
+from Crypto.Hash import MD5
+from Crypto import Random
+from SocketServer import TCPServer, StreamRequestHandler
+import pickle
+
+# Load up our keystore.
+# This should be a dict of names (strings) to RSA keys.
+with open('/flags/rsa.keys', 'r') as f:
+	keys = pickle.load(f)
+
+def keyid(key):
+	return MD5.new(key.publickey().exportKey('DER')).digest()
+
+def getkey(by_id):
+	for key in keys.values():
+		if keyid(key) == by_id:
+			return key
+
+def digest(msg):
+	buf = MD5.new(msg.keyid + ':' + msg.request).digest()
+	print "Message digest is {0}".format(buf.encode('hex'))
+	return buf
+
+def sign(msg):
+	rng = Random.new().read
+	return getkey(msg.keyid).sign(digest(msg), rng)
+
+def verify(msg):
+	return getkey(msg.keyid).verify(digest(msg), msg.signature)
+
+class Request:
+	pass
+
+class Handler(StreamRequestHandler):
+	def start(self):
+		# Ask Bob for his flag, this should be fun.
+		msg = Request()
+		msg.name = 'Alice'
+		msg.request = 'get_flag'
+		msg.keyid = keyid(keys[msg.name])
+		msg.signature = sign(msg)
+		pickle.dump(msg, self.wfile)
+	
+	def get_flag(self, request):
+		# Make sure it's from someone we trust
+		if(request.name not in keys.keys()
+				or request.keyid not in
+				[keyid(key) for key in keys.values()]
+				or request.name == 'Alice'):
+			print "We don't trust this person"
+			return
+		# Verify the signature
+		if(not verify(request)):
+			print "This message was altered"
+			return
+		# Send the goods.
+		pickle.dump(flag, self.wfile)
+
+	def handle(self):
+		request = pickle.load(self.rfile)
+		print "we got: {0}".format(request)
+		if(request.request == 'start'):
+			self.start()
+		if(request.request == 'get_flag'):
+			self.get_flag(request)
+
+for port in range(6666, 6999):
+	try:
+		server = TCPServer(('localhost', port), Handler)
+		print 'server running at port {0}'.format(port)
+		break
+	except:
+		continue
+server.serve_forever()