Class: Rex::Proto::RFB::Cipher

Inherits:
Object
  • Object
show all
Defined in:
lib/rex/proto/rfb/cipher.rb

Overview

A bit of information about the DES algorithm was found here: www.vidarholen.net/contents/junk/vnc.html

In addition, VNC uses two individual 8 byte block encryptions rather than using any block mode (like cbc, ecb, etc).

Class Method Summary collapse

Class Method Details

.decrypt(cipher, password = "\x17\x52\x6b\x06\x23\x4e\x58\x07") ⇒ Object

NOTE: The default password is that of winvnc/etc which is used for encrypting the password(s) on disk/in registry.


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# File 'lib/rex/proto/rfb/cipher.rb', line 64

def self.decrypt(cipher, password = "\x17\x52\x6b\x06\x23\x4e\x58\x07")
  key = self.mangle_password(password)

  # pad the cipher text to 9 bytes
  cipher << ("\x00" * (9 - cipher.length)) if cipher.length < 9

  # NOTE: This only does one 8 byte block
  plain = ''
  c = OpenSSL::Cipher::Cipher.new('des')
  c.decrypt
  c.key = key
  c.update(cipher)
end

.encrypt(plain, password) ⇒ Object


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# File 'lib/rex/proto/rfb/cipher.rb', line 42

def self.encrypt(plain, password)
  key = self.mangle_password(password)

  # pad the plain to 16 chars
  plain << ("\x00" * (16 - plain.length)) if plain.length < 16

  # VNC auth does two 8-byte blocks individually instead supporting some block mode
  cipher = ''
  2.times { |x|
    c = OpenSSL::Cipher::Cipher.new('des')
    c.encrypt
    c.key = key
    cipher << c.update(plain[x*8, 8])
  }

  cipher
end

.mangle_password(password) ⇒ Object


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# File 'lib/rex/proto/rfb/cipher.rb', line 32

def self.mangle_password(password)
  key = ''
  key = password.dup if password
  key.slice!(8,key.length) if key.length > 8
  key << "\x00" * (8 - key.length) if key.length < 8

  # We have to mangle the key so the LSB are kept vs the MSB
  [key.unpack('B*').first.scan(/.{8}/).map! { |e| e.reverse }.join].pack('B*')
end