diff --git a/kishib.py b/kishib.py
index 5dcbc7c..a0706d6 100644
--- a/kishib.py
+++ b/kishib.py
@@ -177,10 +177,13 @@ def parse_hash(auth_hash):
 	return binary
 
 # ------------------------------------------------------------------
-# Public key parsing
+# File format parsing and serialization
 # ------------------------------------------------------------------
 class PubkeyParseError(Exception): pass
 def parse_pubkey(pubkey):
+	# Strip trailing newlines
+	while pubkey[-1:] in (b'\r', b'\n'):
+		pubkey = pubkey[:-1]
 	fields = pubkey.split(b' ')
 
 	# algorithm keymaterial [comment]
@@ -195,15 +198,27 @@ def parse_pubkey(pubkey):
 
 	return algorithm, keymaterial, comment
 
+def serialize_known_hosts(hostname, port, algorithm, keymaterial):
+	if port is None:
+		return b'%s %s %s\n' % (hostname, algorithm, keymaterial)
+	else:
+		return b'[%s]:%i %s %s\n' % (hostname, port, algorithm, keymaterial)
+
+def serialize_authorized_keys(algorithm, keymaterial, comment):
+	if comment is None:
+		return b'%s %s\n' % (algorithm, keymaterial)
+	else:
+		return b'%s %s %s\n' % (algorithm, keymaterial, comment)
+
 # ------------------------------------------------------------------
 # UI
 # ------------------------------------------------------------------
 
 def usage(part = None):
 	if part == 'client' or part is None:
-		print('Usage: %s client [-p <port>] [-i <pubkey>] <host>' % os.path.basename(sys.argv[0]), file = sys.stderr)
+		print('Usage: %s client [-p <port>] [-i <pubkey>] [-o <known_hosts>] [-P <ssh port>] <host>' % os.path.basename(sys.argv[0]), file = sys.stderr)
 	if part =='server' or part is None:
-		print('Usage: %s server [-p <port>] [-i <pubkey>]' % os.path.basename(sys.argv[0]), file = sys.stderr)
+		print('Usage: %s server [-p <port>] [-i <pubkey>] [-o <authorized_keys>]' % os.path.basename(sys.argv[0]), file = sys.stderr)
 	sys.exit(1)
 
 def verify(client_pubkey, server_pubkey):
@@ -236,27 +251,35 @@ def verify(client_pubkey, server_pubkey):
 				error('Could not transfer the keys')
 
 def main():
-	# TODO: Write pubkeys to files
 	if len(sys.argv) < 2:
 		usage()
 
 	command = sys.argv[1]
-	opts, fixed = getopt.gnu_getopt(sys.argv[2:], 'p:i:')
+	opts, fixed = getopt.gnu_getopt(sys.argv[2:], 'p:i:o:P:')
 
 	# TODO: Select an actual port
 	port = 1234
 	pubkey_file = None
+	output_file = None
+	ssh_port = None
 	for switch, arg in opts:
 		if switch == '-p':
 			try:
 				port = int(arg)
 			except ValueError:
 				error('Port needs to be a number')
-		if switch == '-i':
+		elif switch == '-i':
 			pubkey_file = arg
+		elif switch == '-o':
+			output_file = arg
+		elif switch == '-P':
+			try:
+				ssh_port = int(arg)
+			except ValueError:
+				error('Port needs to be a number')
 
 	if command == 'server':
-		if len(fixed) != 0:
+		if len(fixed) != 0 or ssh_port is not None:
 			usage('server')
 
 		if pubkey_file is None:
@@ -281,13 +304,26 @@ def main():
 				with open(pubkey_file, 'rb') as f:
 					server_pubkey = f.read()
 			except IOError as err:
-				error('Could not open server public key file: %s' % err)
+				error('Could not read server public key: %s' % err)
 
 		client_pubkey = server(server_pubkey, port)
 
 		verify(client_pubkey, server_pubkey)
 
-		print(parse_pubkey(client_pubkey))
+		algorithm, keymaterial, comment = parse_pubkey(client_pubkey)
+		authorized_keys_entry = serialize_authorized_keys(algorithm, keymaterial, comment)
+
+		if output_file is None:
+			# Try ~/.ssh/authorized_keys
+			if 'HOME' not in os.environ:
+				error('Cannot locate homedir, $HOME is not set')
+			output_file = os.environ['HOME'] + '/.ssh/authorized_keys'
+
+		try:
+			with open(output_file, 'ab') as f:
+				f.write(authorized_keys_entry)
+		except IOError as err:
+			error('Could not write authorized_keys entry: %s' % err)
 
 	elif command == 'client':
 		if len(fixed) != 1:
@@ -318,7 +354,7 @@ def main():
 				with open(pubkey_file, 'rb') as f:
 					client_pubkey = f.read()
 			except IOError as err:
-				error('Could not open client public key file: %s' % err)
+				error('Could not read client public key: %s' % err)
 
 		host, = fixed
 		# Support internationalized domain names
@@ -328,7 +364,20 @@ def main():
 
 		verify(client_pubkey, server_pubkey)
 
-		print(parse_pubkey(server_pubkey))
+		algorithm, keymaterial, comment = parse_pubkey(server_pubkey)
+		known_hosts_entry = serialize_known_hosts(host.encode(), ssh_port, algorithm, keymaterial)
+
+		if output_file is None:
+			# Try ~/.ssh/known_hosts
+			if 'HOME' not in os.environ:
+				error('Cannot locate homedir, $HOME is not set')
+			output_file = os.environ['HOME'] + '/.ssh/known_hosts'
+
+		try:
+			with open(output_file, 'ab') as f:
+				f.write(known_hosts_entry)
+		except IOError as err:
+			error('Could not write known_hosts entry: %s' % err)
 
 	else:
 		usage()