Shellcode Function Hash Generator

hash.rb

#!/usr/bin/env ruby

def b32_to_i(bin_arr)
  val = 0; bin_arr.each_with_index { |b,i| val += b*(2**(31-i)) }; val
end

def i_to_b32(num)
  val = 31.downto(0).each.map { |i| num[i] }
end

def trunc_to_b32(num)
  b32_to_i(i_to_b32(num))
end

def ror32(reg, offset)
  reg_bits = i_to_b32(reg)
  bits = ((31-offset)-31).upto(31-offset).each.map { |i| reg_bits[i] }
  b32_to_i(bits)
end

def add32(dst, src)
  result = src + dst
  trunc_to_b32(result)
end

def func_hash(str)
  hash_val = 0
  str.each_byte do |b|
    hash_val = ror32(hash_val, 13)
    hash_val = add32(hash_val, b)
  end
  hash_val
end

def to_hex(val)
  "0x" + ("%08x" % [val]).upcase
end

def unicodeify(val)
  val.each_char.map {|b| b + "\x00" }.join('')
end

if ARGV[0] && ARGV[1]
  mod = ARGV[0].upcase + "\x00"
  func = ARGV[1] + "\x00"

  puts to_hex( add32(func_hash(unicodeify(mod)), func_hash(func)) )
else
  puts "This utility generates function hashes for use with Metasploit's"
  puts "block_api.asm, which locates DLL functions at runtime.  block_api.asm"
  puts "was originally written by Stephen Fewer @ Harmony Security."
  puts ""
  puts "Usage: hash.rb <module_name> <function_name>"
end