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---
-- Functions for the SSH-1 protocol. This module also contains functions for
-- formatting key fingerprints.
--
-- @author Sven Klemm <sven@c3d2.de>
-- @copyright Same as Nmap--See http://nmap.org/book/man-legal.html
module(... or "ssh1",package.seeall)
require "bin"
require "bit"
require "math"
require "stdnse"
require "openssl"
--- Retrieve the size of the packet that is being received
-- and checks if it is fully received
--
-- This function is very similar to the function generated
-- with match.numbytes(num) function, except that this one
-- will check for the number of bytes on-the-fly, based on
-- the written on the SSH packet.
--
-- @param buffer The receive buffer
-- @return packet_length, packet_length or nil
-- the return is similar to the lua function string:find()
check_packet_length = function( buffer )
if #buffer < 4 then return nil end
local payload_length, packet_length, offset
offset, payload_length = bin.unpack( ">I", buffer )
local padding = 8 - payload_length % 8
assert(payload_length)
local total = 4+payload_length+padding;
if total > #buffer then return nil end
return total, total;
end
--- Receives a complete SSH packet, even if fragmented
-- this function is an abstraction layer to deal with
-- checking the packet size to know if there is any more
-- data to receive.
--
-- @param socket The socket used to receive the data
-- @return status True or false
-- @return packet The packet received
receive_ssh_packet = function( socket )
local status, packet = socket:receive_buf(check_packet_length, true)
return status, packet
end
--- Fetch an SSH-1 host key.
-- @param host Nmap host table.
-- @param port Nmap port table.
-- @return A table with the following fields: <code>exp</code>,
-- <code>mod</code>, <code>bits</code>, <code>key_type</code>,
-- <code>fp_input</code>, <code>full_key</code>, <code>algorithm</code>, and
-- <code>fingerprint</code>.
fetch_host_key = function(host, port)
local socket = nmap.new_socket()
local status, _
status = socket:connect(host, port)
if not status then return end
-- fetch banner
status = socket:receive_lines(1)
if not status then socket:close(); return end
-- send our banner
status = socket:send("SSH-1.5-Nmap-SSH1-Hostkey\r\n")
if not status then socket:close(); return end
local data, packet_length, padding, offset
status,data = receive_ssh_packet( socket )
socket:close()
if not status then return end
offset, packet_length = bin.unpack( ">i", data )
padding = 8 - packet_length % 8
offset = offset + padding
if padding + packet_length + 4 == #data then
-- seems to be a proper SSH1 packet
local msg_code,host_key_bits,exp,mod,length,fp_input
offset, msg_code = bin.unpack( ">c", data, offset )
if msg_code == 2 then -- 2 => SSH_SMSG_PUBLIC_KEY
-- ignore cookie and server key bits
offset, _, _ = bin.unpack( ">A8i", data, offset )
-- skip server key exponent and modulus
offset, length = bin.unpack( ">S", data, offset )
offset = offset + math.ceil( length / 8 )
offset, length = bin.unpack( ">S", data, offset )
offset = offset + math.ceil( length / 8 )
offset, host_key_bits = bin.unpack( ">i", data, offset )
offset, length = bin.unpack( ">S", data, offset )
offset, exp = bin.unpack( ">A" .. math.ceil( length / 8 ), data, offset )
exp = openssl.bignum_bin2bn( exp )
offset, length = bin.unpack( ">S", data, offset )
offset, mod = bin.unpack( ">A" .. math.ceil( length / 8 ), data, offset )
mod = openssl.bignum_bin2bn( mod )
fp_input = mod:tobin()..exp:tobin()
return {exp=exp,mod=mod,bits=host_key_bits,key_type='rsa1',fp_input=fp_input,
full_key=exp:todec()..' '..mod:todec(),algorithm="RSA1",
fingerprint=openssl.md5(fp_input)}
end
end
end
--- Format a key fingerprint in hexadecimal.
-- @param fingerprint Key fingerprint.
-- @param algorithm Key algorithm.
-- @param bits Key size in bits.
fingerprint_hex = function( fingerprint, algorithm, bits )
fingerprint = stdnse.tohex(fingerprint,{separator=":",group=2})
return ("%d %s (%s)"):format( bits, fingerprint, algorithm )
end
--- Format a key fingerprint in Bubble Babble.
-- @param fingerprint Key fingerprint.
-- @param algorithm Key algorithm.
-- @param bits Key size in bits.
fingerprint_bubblebabble = function( fingerprint, algorithm, bits )
local vowels = {'a','e','i','o','u','y'}
local consonants = {'b','c','d','f','g','h','k','l','m','n','p','r','s','t','v','z','x'}
local s = "x"
local seed = 1
for i=1,#fingerprint+2,2 do
local in1,in2,idx1,idx2,idx3,idx4,idx5
if i < #fingerprint or #fingerprint / 2 % 2 ~= 0 then
in1 = fingerprint:byte(i)
idx1 = (bit.band(bit.rshift(in1,6),3) + seed) % 6 + 1
idx2 = bit.band(bit.rshift(in1,2),15) + 1
idx3 = (bit.band(in1,3) + math.floor(seed/6)) % 6 + 1
s = s .. vowels[idx1] .. consonants[idx2] .. vowels[idx3]
if i < #fingerprint then
in2 = fingerprint:byte(i+1)
idx4 = bit.band(bit.rshift(in2,4),15) + 1
idx5 = bit.band(in2,15) + 1
s = s .. consonants[idx4] .. '-' .. consonants[idx5]
seed = (seed * 5 + in1 * 7 + in2) % 36
end
else
idx1 = seed % 6 + 1
idx2 = 16 + 1
idx3 = math.floor(seed/6) + 1
s = s .. vowels[idx1] .. consonants[idx2] .. vowels[idx3]
end
end
s = s .. 'x'
return ("%d %s (%s)"):format( bits, s, algorithm )
end
--- Format a key fingerprint into a visual ASCII art representation.
--
-- Ported from http://www.openbsd.org/cgi-bin/cvsweb/~checkout~/src/usr.bin/ssh/key.c.
-- @param fingerprint Key fingerprint.
-- @param algorithm Key algorithm.
-- @param bits Key size in bits.
fingerprint_visual = function( fingerprint, algorithm, bits )
local i,j,field,characters,input,fieldsize_x,fieldsize_y,s
fieldsize_x, fieldsize_y = 17, 9
characters = {' ','.','o','+','=','*','B','O','X','@','%','&','#','/','^','S','E'}
-- initialize drawing area
field = {}
for i=1,fieldsize_x do
field[i]={}
for j=1,fieldsize_y do field[i][j]=1 end
end
-- we start in the center and mark it
local x, y = math.ceil(fieldsize_x/2), math.ceil(fieldsize_y/2)
field[x][y] = #characters - 1;
-- iterate over fingerprint
for i=1,#fingerprint do
input = fingerprint:byte(i)
-- each byte conveys four 2-bit move commands
for j=1,4 do
if bit.band( input, 1) == 1 then x = x + 1 else x = x - 1 end
if bit.band( input, 2) == 2 then y = y + 1 else y = y - 1 end
x = math.max(x,1); x = math.min(x,fieldsize_x)
y = math.max(y,1); y = math.min(y,fieldsize_y)
if field[x][y] < #characters - 2 then
field[x][y] = field[x][y] + 1
end
input = bit.rshift( input, 2 )
end
end
-- mark end point
field[x][y] = #characters;
-- build output
s = ('\n+--[%4s %4d]----+\n'):format( algorithm, bits )
for i=1,fieldsize_y do
s = s .. '|'
for j=1,fieldsize_x do s = s .. characters[ field[j][i] ] end
s = s .. '|\n'
end
s = s .. '+-----------------+\n'
return s
end
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