rspamd/rules/bitcoin.lua

--[[
Copyright (c) 2019, Vsevolod Stakhov <vsevolod@highsecure.ru>

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
]]--

-- Bitcoin filter rules

local fun = require "fun"
local bit = require "bit"
local off = 0
local base58_dec = fun.tomap(fun.map(
    function(c)
      off = off + 1
      return c,(off - 1)
    end,
    "123456789ABCDEFGHJKLMNPQRSTUVWXYZabcdefghijkmnopqrstuvwxyz"))

local function is_traditional_btc_address(word)
  local hash = require "rspamd_cryptobox_hash"

  local bytes = {}
  for i=1,25 do bytes[i] = 0 end
  -- Base58 decode loop
  fun.each(function(ch)
    local acc = base58_dec[ch] or 0
    for i=25,1,-1 do
      acc = acc + (58 * bytes[i]);
      bytes[i] = acc % 256
      acc = math.floor(acc / 256);
    end
  end, word)
  -- Now create a validation tag
  local sha256 = hash.create_specific('sha256')
  for i=1,21 do
    sha256:update(string.char(bytes[i]))
  end
  sha256 = hash.create_specific('sha256', sha256:bin()):bin()

  -- Compare tags
  local valid = true
  for i=1,4 do
    if string.sub(sha256, i, i) ~= string.char(bytes[21 + i]) then
      valid = false
    end
  end

  return valid
end

-- Beach32 checksum combiner
local function polymod(...)
  local chk = 1;
  local gen = {0x3b6a57b2, 0x26508e6d, 0x1ea119fa, 0x3d4233dd, 0x2a1462b3};
  for _,t in ipairs({...}) do
    for _,v in ipairs(t) do
      local top = bit.rshift(chk, 25)

      chk = bit.bxor(bit.lshift(bit.band(chk, 0x1ffffff), 5), v)
      for i=1,5 do
        if bit.band(bit.rshift(top, i - 1), 0x1) ~= 0 then
          chk = bit.bxor(chk, gen[i])
        end
      end
    end
  end

  return chk
end

-- Beach32 expansion function
local function hrpExpand(hrp)
  local ret = {}
  fun.each(function(byte)
    ret[#ret + 1] = bit.rshift(byte, 5)
  end, fun.map(string.byte, fun.iter(hrp)))
  ret[#ret + 1] = 0
  fun.each(function(byte)
    ret[#ret + 1] = bit.band(byte, 0x1f)
  end, fun.map(string.byte, fun.iter(hrp)))

  return ret
end

local function verify_beach32_cksum(hrp, elts)
  return polymod(hrpExpand(hrp), elts) == 1
end

local function gen_bleach32_table(input)
  local d = {}
  local i = 1
  local res = true
  local charset = 'qpzry9x8gf2tvdw0s3jn54khce6mua7l'

  fun.each(function(byte)
    if res then
      local pos = charset:find(byte)
      if not pos then
        res = false
      else
        d[i] = pos - 1
        i = i + 1
      end
    end
  end, fun.iter(input))

  return res and d or nil
end

local function is_segwit_bech32_address(word)
  local semicolon_pos = string.find(word, ':')
  if semicolon_pos then
    word = string.sub(word, semicolon_pos + 1)
  end

  local prefix = word:sub(1, 3)

  if prefix == 'bc1' or prefix:sub(1, 1) == '1' or prefix:sub(1, 1) == '3' then
    -- Strip beach32 prefix in bitcoin
    word = word:lower()
    local last_one_pos = word:find('1[^1]*$')
    if not last_one_pos or (last_one_pos < 1 or last_one_pos + 7 > #word) then
      return false
    end
    local hrp = word:sub(1, last_one_pos - 1)
    local addr = word:sub(last_one_pos + 1, -1)
    local decoded = gen_bleach32_table(addr)

    if decoded then
      return verify_beach32_cksum(hrp, decoded)
    end
  else
    -- BCH address
    -- 1 byte address type (who cares)
    -- XXX bytes address hash (who cares)
    -- 40 bit checksum
    local rspamd_util = require 'rspamd_util'
    local decoded = rspamd_util.decode_base32(word:lower(), 'bleach')

    if decoded then
      local bytes = decoded:bytes()

      -- The version byte’s most signficant bit is reserved and must be 0.
      -- The 4 next bits indicate the type of address and the 3 least significant bits indicate the size of the hash.
      local version = bit.band(bytes[1], 128)
      local addr_type = bit.rshift(bit.band(bytes[1], 120), 3)
      local _ = bit.band(bytes[1], 7) -- hash size

      if version == 0 and (addr_type == 0 or addr_type == 8)then
        -- TODO: Add checksum validation some day

        return true
      end
    end
  end
end


rspamd_config:register_symbol{
  name = 'BITCOIN_ADDR',
  description = 'Message has a valid bitcoin wallet address',
  callback = function(task)
    local rspamd_re = require "rspamd_regexp"

    local btc_wallet_re = rspamd_re.create_cached('^[13LM][1-9A-Za-z]{25,34}$')
    local segwit_wallet_re = rspamd_re.create_cached('^(?:bc1|[13]|(?:[^:]*:))?[qpzry9x8gf2tvdw0s3jn54khce6mua7l]{14,}$', 'i')
    local words_matched = {}
    local segwit_words_matched = {}
    local valid_wallets = {}

    for _,part in ipairs(task:get_text_parts() or {}) do
      local pw = part:filter_words(btc_wallet_re, 'raw', 3)

      if pw and #pw > 0 then
        for _,w in ipairs(pw) do
          words_matched[#words_matched + 1] = w
        end
      end

      pw = part:filter_words(segwit_wallet_re, 'raw', 3)
      if pw and #pw > 0 then
        for _,w in ipairs(pw) do
          segwit_words_matched[#segwit_words_matched + 1] = w
        end
      end
    end

    for _,word in ipairs(words_matched) do
      local valid = is_traditional_btc_address(word)
      if valid then
        valid_wallets[#valid_wallets + 1] = word
      end
    end
    for _,word in ipairs(segwit_words_matched) do
      local valid = is_segwit_bech32_address(word)
      if valid then
        valid_wallets[#valid_wallets + 1] = word
      end
    end

    if #valid_wallets > 0 then
      return true,1.0,valid_wallets
    end
  end,
  score = 0.0,
  group = 'scams'
}