commit 87c9871: [Feature] Support segwit BTC addresses, fix LTC verification

[Vsevolod Stakhov]

Author: Vsevolod Stakhov
Date: 2019-10-23 15:53:27 +0100
URL: https://github.com/rspamd/rspamd/commit/87c987155c06650750c355e8a0fd08299692a498 (HEAD -> master)

[Feature] Support segwit BTC addresses, fix LTC verification

---
 rules/bitcoin.lua | 154 +++++++++++++++++++++++++++++++++++++++++++-----------
 1 file changed, 123 insertions(+), 31 deletions(-)

diff --git a/rules/bitcoin.lua b/rules/bitcoin.lua
index 0b611796d..86380badf 100644
--- a/rules/bitcoin.lua
+++ b/rules/bitcoin.lua
@@ -17,6 +17,7 @@ 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)
@@ -25,16 +26,127 @@ local base58_dec = fun.tomap(fun.map(
     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 is_segwit_bech32_address(word)
+  local has_upper, has_lower, has_invalid
+
+  if #word > 90 then return false end
+
+  fun.each(function(ch)
+    if ch < 33 or ch > 126 then
+      has_invalid = true
+    elseif ch >= 97 and ch <= 122 then
+      has_lower = true
+    elseif ch >= 65 and ch <= 90 then
+      has_upper = true;
+    end
+  end, fun.map(string.byte, fun.iter(word)))
+
+  if has_invalid or (has_lower and has_upper) then
+    return false
+  end
+
+  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 d = {}
+  local charset = 'qpzry9x8gf2tvdw0s3jn54khce6mua7l';
+  for i=last_one_pos + 1,#word do
+    local c = word:sub(i, i)
+    local pos = charset:find(c)
+
+    if not pos then
+      return false
+    end
+    d[#d + 1] = pos - 1
+  end
+
+  return verify_beach32_cksum(hrp, d)
+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 hash = require "rspamd_cryptobox_hash"
 
-    local btc_wallet_re = rspamd_re.create_cached('^[13][1-9A-Za-z]{25,34}$')
-    local ltc_wallet_re = rspamd_re.create_cached('^[LM3][a-km-zA-HJ-NP-Z1-9]{26,33}$')
+    local btc_wallet_re = rspamd_re.create_cached('^[13LM][1-9A-Za-z]{25,34}$')
+    local segwit_wallet_re = rspamd_re.create_cached('^[b][c]1[qpzry9x8gf2tvdw0s3jn54khce6mua7l]{14,74}$', 'i')
     local words_matched = {}
+    local segwit_words_matched = {}
     local valid_wallets = {}
 
     for _,part in ipairs(task:get_text_parts() or {}) do
@@ -46,42 +158,22 @@ rspamd_config:register_symbol{
         end
       end
 
-      pw = part:filter_words(ltc_wallet_re, 'raw', 3)
+      pw = part:filter_words(segwit_wallet_re, 'raw', 3)
       if pw and #pw > 0 then
         for _,w in ipairs(pw) do
-          -- Do not validate, LTC regexp is more strict than BTC one, maybe do it in future
-          valid_wallets[#valid_wallets + 1] = w
+          segwit_words_matched[#segwit_words_matched + 1] = w
         end
       end
     end
 
     for _,word in ipairs(words_matched) do
-      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
+      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