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##
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# This module requires Metasploit: https://metasploit.com/download
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# Current source: https://github.com/rapid7/metasploit-framework
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##
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class MetasploitModule < Msf::Encoder::Xor
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  def initialize
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    super(
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      'Name'             => 'XOR Encoder',
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      'Description'      => 'An x64 XOR encoder. Uses an 8 byte key and takes advantage of x64 relative addressing.',
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      'Author'           => [ 'sf' ],
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      'Arch'             => ARCH_X64,
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      'License'          => MSF_LICENSE,
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      'Decoder'          =>
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        {
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          'KeySize'      => 8,
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          'KeyPack'      => 'Q',
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          'BlockSize'    => 8,
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        }
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      )
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  end
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  # Indicate that this module can preserve some registers
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  # ...which is currently not true. This is a temp fix
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  # until the full preserve_registers functionality is
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  # implemented.
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  def can_preserve_registers?
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    true
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  end
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  def decoder_stub( state )
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    # calculate the (negative) block count . We should check this against state.badchars.
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    block_count = [-( ( (state.buf.length - 1) / state.decoder_key_size) + 1)].pack( "V" )
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    decoder =   "\x48\x31\xC9" +                 # xor rcx, rcx
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          "\x48\x81\xE9" + block_count +   # sub ecx, block_count
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          "\x48\x8D\x05\xEF\xFF\xFF\xFF" + # lea rax, [rel 0x0]
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          "\x48\xBBXXXXXXXX" +             # mov rbx, 0x????????????????
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          "\x48\x31\x58\x27" +             # xor [rax+0x27], rbx
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          "\x48\x2D\xF8\xFF\xFF\xFF" +     # sub rax, -8
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          "\xE2\xF4"                       # loop 0x1B
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    state.decoder_key_offset = decoder.index( 'XXXXXXXX' )
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    return decoder
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  end
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end
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