Added an explanation to the front page

WebServer/static/exchange_client.py

@@ -1,3 +1,5 @@
+import logging
+from logging.config import dictConfig
 from typing import Optional, Callable
 
 from Crypto.PublicKey.ECC import EccKey
@@ -7,6 +9,45 @@ from SantaExchange.MessageHandler import MessageHandler
 from SantaExchange.SantasBrain import Brain
 from SantaExchange.UserInterface import UserInterface
 
+logging_function: Optional[Callable[[str], None]] = None
+
+
+class ExchangeLogger(logging.Handler):
+	def emit(self, record: logging.LogRecord):
+		if logging_function is not None:
+			logging_function(record.message)
+
+
+LOGGING_SETTINGS = {
+	'version': 1,
+	'disable_existing_loggers': False,
+	'formatters': {
+		'std_formatter': {'format': '%(message)s'}
+	},
+	'handlers': {
+		'stdhandler': {
+			'class': 'logging.StreamHandler',
+			'formatter': 'std_formatter',
+			'stream': 'ext://sys.stdout'
+		},
+		'ExchangeLogger': {
+			'class': f'{__name__}.ExchangeLogger',
+			'formatter': 'std_formatter',
+			'level': 'INFO'
+		}
+	},
+	'loggers': {
+		'root': {
+			'handlers': ['stdhandler', 'ExchangeLogger'],
+			'level': 'NOTSET',
+			'propagate': True
+		}
+	}
+}
+
+dictConfig(LOGGING_SETTINGS)
+
+
 class ExchangeClient(MessageHandler, UserInterface):
 	def __init__(self, send_message_function, receive_user_function, announce_recipient_function):
 		MessageHandler.__init__(self)

WebServer/static/exchange_worker.js

@@ -21,13 +21,13 @@ async function prepare() {
 	}
 
 	function printLogs(record) {
-	    console.log(record);
+	    postMessage({type: 'status', stage: 'exchange', text: record});
 	}
 
 	pyodide.globals.set('send_message', sendMessage);
 	pyodide.globals.set('receive_user', receiveUser);
 	pyodide.globals.set('announce_recipient', announceRecipient);
-	pyodide.globals.set('print_logs_function', printLogs);
+	pyodide.globals.set('logging_function', printLogs);
 
 	pyodide.runPython(`
         exchange_worker = ExchangeClient(send_message, receive_user, announce_recipient)

WebServer/static/style.css

@@ -36,4 +36,8 @@ textarea {
 	width: 30vw;
 	height: 20vh;
 	font-size: 20px;
+}
+
+.leftjust {
+    text-align: left;
 }

WebServer/templates/exchange.html

@@ -8,19 +8,28 @@
 </head>
 <body>
 	<h1>Santa exchange</h1>
+	<p id="santaexchangename">This santa exchange is named: </p>
+	<button onclick="copyLinkToClipboard();">Copy link to clipboard</button><br /><br /><br />
+	<p>Status:</p>
+	<pre id="statusParagraph"></pre>
 	<label for="own_name">Your name: </label><br /><input type="text" id="own_name" /><br />
 	<br />
 	<label for="info_for_santa">Info for your santa (e.g. shipping address or similar):</label><br />
 	<textarea id="info_for_santa"></textarea><br />
 	<button id="submit_info_button" onclick="submitInfo();">Submit your info</button>
 	<br /><br /><br />
-	<pre id="statusParagraph"></pre>
 	<button id="start_exchange_button" onclick="submitStart();">Start with current participants</button>
 	<p>Current participants:</p>
 	<ul id='participantList'>
 
 	</ul>
 	<script type="text/javascript">
+		document.getElementById('santaexchangename').innerHTML += window.location.pathname.substring(1);
+
+		function copyLinkToClipboard() {
+			navigator.clipboard.writeText(window.location.href);
+		}
+
 		const socket = io();
 		const client_id = Math.floor(Math.random() * 2**64)
 

WebServer/templates/index.html

@@ -9,10 +9,11 @@
 <body>
 	<div class="bodyDiv">
 		<h1>DecentraSanta</h1>
-		<p>Welcome to the decentralised secret santa exchange. This website uses cryptography to distribute secret santas
-			in such a way that no one but you, not even the server the communication goes through, can know who you're
-			giving a
-			gift to.</p>
+		<p>
+			Welcome to the decentralised secret santa exchange. This website uses cryptography to distribute secret
+			santas in such a way that no one but you, not even the server the communication goes through, can know who
+			you're giving a gift to.
+		</p>
 
 		<p>You can either start a new secret santa exchange, or join an existing one.</p>
 
@@ -23,6 +24,48 @@
 		<input type="text" id="existing_address" />
 		<br/>
 		<button id="join_existing" onclick="onJoinExchange();">Join existing exchange</button>
+		<br /><br /><br /><br />
+		<p>
+			<b>
+				WARNING: I have partially rolled my own crypto for this project. Please don't use it for anything serious!
+			</b>
+		</p>
+		<p class="leftjust">
+			How does this work: the simplified analogy is that we build a deck of cards numbered from 1 up to the number
+			of participants. This deck is shuffled, and each participant draws a card. The cards determine the secret
+			santa order: The participant who draws card 1 is the secret santa for the participant who draws card 2, who
+			is secret santa for the participant who draws card 3, and so forth.
+		</p>
+		<p>
+			In this analogy, once the participants have drawn their cards, they each anonymously put up a mailbox that
+			is marked with number of the card they drew. Each participant then puts their name and address (secretly)
+			into the mailbox with the number of their secret santa. Finally, they secretly open their mailboxes to find
+			the name and address of the recipient of their gifts.
+		</p>
+		<p>
+			More technically: the shuffling and drawing of the cards is done using the
+			<a href="https://people.csail.mit.edu/rivest/pubs/SRA81.pdf">mental poker algorithm described by Shamir,
+			Rivest, and Adleman.</a> This algorithm depends on a commutative encryption algorithm. Here, I have used the
+			SRA algorithm, which is a modification of the RSA algorithm where the modulus used to encrypt and decrypt
+			values is public, but the both the encryption and decryption keys are kept private. I couldn't find any
+			Python libraries that implement this algorithm, so I have implemented it on my own. I make no guarantees
+			that this is secure in any way.
+		</p>
+		<p>
+			In the analogy above, the mailboxes represent public key cryptography. It is possible to anonymously announce
+			a participant's public key using the same mental poker algorithm from above: each participant publishes a
+			"card" containing, in encrypted form, their public key and the card number they drew in the previous step.
+			Each other participant then encrypts this card with their own key. Once all the cards have been encrypted
+			in this way, each participant then removes their key, shuffles the deck, and applies a new key (which should
+			make it impossible to correlate cards before and after shuffling). Finally, each participant removes their
+			key from each of the cards. This should give a deck of cards containing participant numbers and public keys,
+			shuffled in such a way that it is impossible to know which card originated from which participant.
+		</p>
+		<p>
+			Finally, each participant publishes their name and address, encrypted so that only their secret santa can read
+			it. Each participant must then try to decrypt all of these encrypted messages until their gift receiver is found.
+		</p>
+		<p><a href="https://gitea.martinserver.no/martin/DecentraSanta">The source code for this web site can be found here!</a></p>
 	</div>
 
 	<script type="text/javascript">

src/SantaExchange/SantasBrain.py

@@ -216,7 +216,6 @@ class Brain:
 					or self.announcement_build_cipher is None
 					or self.announcement_shuffle_cipher is None
 			):
-				logger.debug('Building ciphers')
 				should_continue = self.build_ciphers()
 				if not should_continue:
 					return messages_to_send
@@ -226,7 +225,6 @@ class Brain:
 
 			# Shuffle cards
 			if not self.sent_card_shuffling:
-				logger.debug('Shuffling vards')
 				shuffle_message = self.build_shuffle_message(all_participants)
 				if shuffle_message is None:
 					return messages_to_send
@@ -235,7 +233,6 @@ class Brain:
 
 			# Decrypt shuffled cards
 			if not self.sent_card_decryption:
-				logger.debug('Decrypting shuffled cards')
 				decrypt_cards_message = self.build_decrypt_cards_message(all_participants)
 				if decrypt_cards_message is None:
 					return messages_to_send
@@ -359,6 +356,7 @@ class Brain:
 
 			received_seeds.append(received_seed)
 		# Next, create a combined random seed from all the provided seeds
+		logger.info('Building cryptographic ciphers')
 		number_of_seed_bytes = max(len(seed) for seed in received_seeds)
 		total_seed = b'\0' * number_of_seed_bytes
 		for received_seed in received_seeds:
@@ -401,6 +399,7 @@ class Brain:
 			card_deck = [card for card in message.get_cards()]
 
 		# Shuffle by drawing random numbers from secret
+		logger.info('Shuffling encrypted cards')
 		shuffled_deck = []
 		while len(card_deck) > 0:
 			drawn_card = secrets.randbelow(len(card_deck))
@@ -432,6 +431,7 @@ class Brain:
 		if message is None:
 			return None
 
+		logger.info('Decrypting shuffled cards')
 		card_deck = message.get_cards()
 		decrypted_cards = []
 		for index, card_value in enumerate(card_deck):
@@ -448,7 +448,7 @@ class Brain:
 		return ShuffleMessage(self.own_name, decrypted_cards, DECRYPT_CARDS_STAGE)
 
 	def decrypt_card_value(self, card: bytes):
-		logger.debug('Decrypting own drawn card')
+		logger.info('Decrypting drawn card')
 		decrypted_card_bytes = self.card_exchange_cipher.decode(card)
 		if decrypted_card_bytes not in self.card_values:
 			logging.critical(f'Received an invalid card after shuffling. Secret santa exchange failed!')
@@ -477,6 +477,7 @@ class Brain:
 
 			card_deck = [card for card in message.get_cards()]
 
+		logger.info('Creating anonymous message')
 		anonymous_message = {
 			'card_no': self.card_drawn,
 			'key': self.secret_key.public_key().export_key(format='OpenSSH')
@@ -515,6 +516,7 @@ class Brain:
 		if card_deck is None:
 			return None
 
+		logger.info('Building deck of anonymous messages')
 		encrypted_deck = []
 		for index, card_value in enumerate(card_deck):
 			if index == own_index:
@@ -553,6 +555,7 @@ class Brain:
 		if card_deck is None:
 			return None
 
+		logger.info('Shuffling anonymous messages')
 		shuffled_cards = []
 		while len(card_deck) > 0:
 			draw_number = secrets.randbelow(len(card_deck))
@@ -595,6 +598,7 @@ class Brain:
 		if card_deck is None:
 			return None
 
+		logger.info('Decrypting anonymous messages')
 		decrypted_deck = [self.announcement_shuffle_cipher.decode(card_value) for card_value in card_deck]
 		shuffle_message = ShuffleMessage(self.own_name, decrypted_deck, DECRYPT_ANONYMOUS_STAGE)
 
@@ -646,6 +650,7 @@ class Brain:
 		if self.anonymous_keys is None:
 			return None
 
+		logger.info("Creating encrypted announcement for secret santa")
 		santa_card = (self.card_drawn - 1) % len(all_participants)
 
 		santa_key = self.anonymous_keys[santa_card]