Implement mpint2 read/write and tests. Refactor (Read|Write)Buf.

ssh-audit.py

@@ -155,19 +155,38 @@ class ReadBuf(object):
 	def read(self, size):
 		return self._buf.read(size)
 	
-	def read_line(self):
-		return self._buf.readline().rstrip().decode('utf-8')
+	def read_byte(self):
+		return struct.unpack('B', self.read(1))[0]
+	
+	def read_bool(self):
+		return self.read_byte() != 0
 	
 	def read_int(self):
 		return struct.unpack('>I', self.read(4))[0]
 	
-	def read_bool(self):
-		return struct.unpack('b', self.read(1))[0] != 0
-	
 	def read_list(self):
 		list_size = self.read_int()
 		return self.read(list_size).decode().split(',')
 	
+	def read_string(self):
+		n = self.read_int()
+		return self.read(n)
+	
+	def read_mpint2(self):
+		# NOTE: Section 5 @ https://www.ietf.org/rfc/rfc4251.txt 
+		r, v = 0, self.read_string()
+		if len(v) == 0:
+			return r
+		pad, sf = (b'\xff', '>i') if ord(v[0:1]) & 0x80 else (b'\x00', '>I')
+		if len(v) % 4:
+			v = pad * (4 - (len(v) % 4)) + v
+		for i in range(0, len(v), 4):
+			r = (r << 32) | struct.unpack(sf, v[i:i + 4])[0]
+		return r
+	
+	def read_line(self):
+		return self._buf.readline().rstrip().decode('utf-8')
+
 
 class WriteBuf(object):
 	def __init__(self, data=None):
@@ -176,31 +195,40 @@ class WriteBuf(object):
 	
 	def write(self, data):
 		self._wbuf.write(data)
+		return self
 	
 	def write_byte(self, v):
-		self.write(struct.pack('>B', v))
+		return self.write(struct.pack('B', v))
 	
 	def write_bool(self, v):
-		self.write_byte(1 if v else 0)
+		return self.write_byte(1 if v else 0)
 	
 	def write_int(self, v):
-		self.write(struct.pack('>I', v))
+		return self.write(struct.pack('>I', v))
 	
 	def write_string(self, v):
 		if not isinstance(v, bytes):
 			v = bytes(bytearray(v, 'utf-8'))
-		n = len(v)
-		self.write(struct.pack('>I', n))
-		self.write(v)
+		self.write_int(len(v))
+		return self.write(v)
 	
 	def write_list(self, v):
-		self.write_string(','.join(v))
+		self.write_string(u','.join(v))
 	
-	def write_mpint(self, v):
-		length = v.bit_length() // 8 + 1
+	def write_mpint2(self, v):
+		# NOTE: Section 5 @ https://www.ietf.org/rfc/rfc4251.txt 
+		length = v.bit_length() // 8 + (1 if v != 0 else 0)
 		data = [(v >> i * 8) & 0xff for i in reversed(range(length))]
+		if length > 1 and data[0] == 0xff and data[1] & 0x80:
+			data.pop(0)
 		data = bytes(bytearray(data))
-		self.write_string(data)
+		return self.write_string(data)
+	
+	def write_flush(self):
+		payload = self._wbuf.getvalue()
+		self._wbuf.truncate(0)
+		self._wbuf.seek(0)
+		return payload
 
 
 class SSH(object):
@@ -559,9 +587,7 @@ class SSH(object):
 			return packet_type, payload
 		
 		def send_packet(self):
-			payload = self._wbuf.getvalue()
-			self._wbuf.truncate(0)
-			self._wbuf.seek(0)
+			payload = self.write_flush()
 			padding = -(len(payload) + 5) % 8
 			if padding < 4:
 				padding += 8
@@ -597,7 +623,7 @@ class KexDH(object):
 		self.__x = r.randrange(2, self.__q)
 		self.__e = pow(self.__g, self.__x, self.__p)
 		s.write_byte(SSH.Protocol.MSG_KEXDH_INIT)
-		s.write_mpint(self.__e)
+		s.write_mpint2(self.__e)
 		s.send_packet()
 
 

test/test_protocol.py

@@ -0,0 +1,37 @@
+#!/usr/bin/env python
+# -*- coding: utf-8 -*-
+import pytest
+import re
+
+
+class TestProtocol(object):
+	@pytest.fixture(autouse=True)
+	def init(self, ssh_audit):
+		self.rbuf = ssh_audit.ReadBuf
+		self.wbuf = ssh_audit.WriteBuf
+	
+	def _b(self, v):
+		v = re.sub(r'\s', '', v)
+		data = [int(v[i * 2:i * 2 + 2], 16) for i in range(len(v) // 2)]
+		return bytes(bytearray(data))
+	
+	def test_mpint2_write(self):
+		wbuf, _b = self.wbuf(), self._b
+		mpint = lambda x: wbuf.write_mpint2(x).write_flush()
+		assert mpint(0x0)               == _b('00 00 00 00')
+		assert mpint(0x80)              == _b('00 00 00 02 00 80')
+		assert mpint(0x9a378f9b2e332a7) == _b('00 00 00 08 09 a3 78 f9 b2 e3 32 a7')
+		assert mpint(-0x1234)           == _b('00 00 00 02 ed cc')
+		assert mpint(-0xdeadbeef)       == _b('00 00 00 05 ff 21 52 41 11')
+		assert mpint(-0x80)             == _b('00 00 00 01 80')
+	
+	def test_mpint2_read(self):
+		rbuf, _b = self.rbuf, self._b
+		mpint = lambda x: rbuf(x).read_mpint2()
+		assert mpint(_b('00 00 00 00'))                         == 0x00
+		assert mpint(_b('00 00 00 02 00 80'))                   == 0x80
+		assert mpint(_b('00 00 00 08 09 a3 78 f9 b2 e3 32 a7')) == 0x9a378f9b2e332a7
+		assert mpint(_b('00 00 00 02 ed cc'))                   == -0x1234
+		assert mpint(_b('00 00 00 05 ff 21 52 41 11'))          == -0xdeadbeef
+		assert mpint(_b('00 00 00 01 80'))                      == -0x80
+		assert mpint(_b('00 00 00 02 ff 80'))                   == -0x80