Lua 中的 RSA 加解密实现

　　记得之前，部门某款游戏陆陆续续收到一些玩家反馈，抱怨在登录游戏时会等待很久。初步排查后基本断定可能是此游戏的登录服务器程序某块代码有问题，于是即安排了服务器同事作排查分析但一直无果。

　　之后我时间有了空余，开始协助排查调试。简单了解了此登录服务器的逻辑处理流程后（接收到经过加密的 HTTP 登陆请求-->解密数据包-->去数据库查询对应的玩家信息并作验证），一开始我简单认为瓶颈估计出现在“去数据库查询对应的玩家信息”这步，毕竟磁盘 IO 明显比较耗时，于是未作更多考虑，将每次登陆验证都去数据库查询的操作改为维护一个哈希表存储玩家信息，并在程序启动时载入近几日登陆过游戏的玩家信息至此哈希表中，且当从数据库查询出尚未缓存的玩家信息后即也存入哈希表以保证最多只有一次而非每次都要作磁盘 IO。本以为经过改进后的登录服务器已解决了问题，但内部压测表明，登陆耗时较长问题依旧存在，改进版本的登录服务器程序几无效果！

　　打脸之下，好奇心大起，于是再认真研究了登陆验证处理流程，之后分别在可能的瓶颈代码前后加上耗时打印（多么简单老土的做法:)），很快有了“重大”发现：处理 RSA 解密的代码，在 64 位四核 CentOS 上每次解密处理耗时约需 50ms 左右！

　　印象里非对称加解密比较慢，但如此不正常的慢，似乎有违常理，当时即用 Golang 撸了个一样的 RSA 解密程序，对比之下，耗时大大减少，于是很明显，基本可以断定，此游戏的登录服务器程序的 RSA 解密模块有较大的性能问题。

　　注：此游戏的服务器端程序基于 Pomelo 框架，完全由 Node.js 开发（也正因此，常见的性能分析等工具如 AQTime 等派不上用场）。

　　啰嗦了这么多，其实只想说两点：

1. 可能吧，Node.js 虽然三方库大把，但不少库的质量恐怕...当然，网上似乎早已有类似告诫
2. CPU 密集型操作，静态语言可能更适合（虽然譬如 Node.js，网络性能方面粗测很不错）

　　所以最近，趁着对 Lua 还有点印象，在参考研究了一些网上资源后，搞了套简单的在 Lua 中通过 ffi 方式调用由 C 实现的 RSA 加解密例程的方案，如下（编译后的 so 文件及源代码等压缩包可从这里下载）。

　　纯 C 实现的 RSA 加解密程序（通过 OpenSSL 调用）：

/*******************************************************************************************
 *
 *  Copyright (C) Ravishanker Kusuma / ecofast.  All Rights Reserved.
 *
 *  File: rsautils.c
 *  Date: 2017/12/01
 *  Desc: RSA Encryption & Decryption utils with OpenSSL in C
 *
 *  Thks: http://hayageek.com/rsa-encryption-decryption-openssl-c/
 *
 *  Compilation Command: gcc rsautils.c -fPIC -shared -lssl -lcrypto -o librsa.so
 *******************************************************************************************/

#include <openssl/pem.h>
#include <openssl/ssl.h>
#include <openssl/rsa.h>
#include <openssl/evp.h>
#include <openssl/bio.h>

const int padding = RSA_PKCS1_OAEP_PADDING;

int public_encrypt(unsigned char* data, int data_len, unsigned char* key, unsigned char* encrypted)
{
    int ret = -;
    BIO* keybio = BIO_new_mem_buf(key, -);
    if (keybio != NULL)
    {
        RSA* rsa = NULL;
        rsa = PEM_read_bio_RSA_PUBKEY(keybio, &rsa, NULL, NULL);
        if (rsa != NULL)
        {
            ret = RSA_public_encrypt(data_len, data, encrypted, rsa, padding);
            RSA_free(rsa);
        }
        BIO_free_all(keybio);
    }
    return ret;
}

int private_decrypt(unsigned char* enc_data, int data_len, unsigned char* key, unsigned char* decrypted)
{
    int ret = -;
    BIO* keybio = BIO_new_mem_buf(key, -);
    if (keybio != NULL)
    {
        RSA* rsa = NULL;
        rsa = PEM_read_bio_RSAPrivateKey(keybio, &rsa, NULL, NULL);
        if (rsa != NULL)
        {
            ret = RSA_private_decrypt(data_len, enc_data, decrypted, rsa, padding);
            RSA_free(rsa);
        }
        BIO_free_all(keybio);
    }
    return ret;
}

　　而 HTTP 传输，base64 编码自然少不了（源自 这里）：

local function divide_string( str, max, fillChar )
   fillChar = fillChar or ""
   local result = {}

   local start =
   for i = , #str do
      if i % max ==  then
         table.insert( result, str:sub( start, i ) )
         start = i +
      elseif i == #str then
         table.insert( result, str:sub( start, i ) )
      end
   end

   return result
end

local function number_to_bit( num, length )
   local bits = {}

   while num >  do
      local rest = math.floor( math.fmod( num,  ) )
      table.insert( bits, rest )
      num = ( num - rest ) /
   end

   while #bits < length do
      table.insert( bits, "" )
   end

   return string.reverse( table.concat( bits ) )
end

local function ignore_set( str, set )
   if set then
      str = str:gsub( "["..set.."]", "" )
   end
   return str
end

local function pure_from_bit( str )
   return ( str:gsub( '........', function ( cc )
               return string.char( tonumber( cc,  ) )
            end ) )
end

local function unexpected_char_error( str, pos )
   local c = string.sub( str, pos, pos )
   return string.format( "unexpected character at position %d: '%s'", pos, c )
end

--------------------------------------------------------------------------------

local basexx = {}

--------------------------------------------------------------------------------
-- base2(bitfield) decode and encode function
--------------------------------------------------------------------------------

local bitMap = { o = "", i = "", l = "" }

function basexx.from_bit( str, ignore )
   str = ignore_set( str, ignore )
   str = string.lower( str )
   str = str:gsub( '[ilo]', function( c ) return bitMap[ c ] end )
   local pos = string.find( str, "[^01]" )
   if pos then return nil, unexpected_char_error( str, pos ) end

   return pure_from_bit( str )
end

function basexx.to_bit( str )
   return ( str:gsub( '.', function ( c )
               local byte = string.byte( c )
               local bits = {}
               for i = , do
                  table.insert( bits, byte %  )
                  byte = math.floor( byte /  )
               end
               return table.concat( bits ):reverse()
            end ) )
end

--------------------------------------------------------------------------------
-- base16(hex) decode and encode function
--------------------------------------------------------------------------------

function basexx.from_hex( str, ignore )
   str = ignore_set( str, ignore )
   local pos = string.find( str, "[^%x]" )
   if pos then return nil, unexpected_char_error( str, pos ) end

   return ( str:gsub( '..', function ( cc )
               return string.char( tonumber( cc,  ) )
            end ) )
end

function basexx.to_hex( str )
   return ( str:gsub( '.', function ( c )
               return string.format('%02X', string.byte( c ) )
            end ) )
end

--------------------------------------------------------------------------------
-- generic function to decode and encode base32/base64
--------------------------------------------------------------------------------

local function from_basexx( str, alphabet, bits )
   local result = {}
   for i = , #str do
      local c = string.sub( str, i, i )
      if c ~= '=' then
         local index = string.find( alphabet, c, , true )
         if not index then
            return nil, unexpected_char_error( str, i )
         end
         table.insert( result, number_to_bit( index - , bits ) )
      end
   end

   local value = table.concat( result )
   local pad = #value %
   return pure_from_bit( string.sub( value, , #value - pad ) )
end

local function to_basexx( str, alphabet, bits, pad )
   local bitString = basexx.to_bit( str )

   local chunks = divide_string( bitString, bits )
   local result = {}
   for key,value in ipairs( chunks ) do
      if ( #value < bits ) then
         value = value .. string.rep( '', bits - #value )
      end
      local pos = tonumber( value,  ) +
      table.insert( result, alphabet:sub( pos, pos ) )
   end

   table.insert( result, pad )
   return table.concat( result )
end

--------------------------------------------------------------------------------
-- rfc 3548: http://www.rfc-editor.org/rfc/rfc3548.txt
--------------------------------------------------------------------------------

local base32Alphabet = "ABCDEFGHIJKLMNOPQRSTUVWXYZ234567"
local base32PadMap = { "", "======", "====", "===", "=" }

function basexx.from_base32( str, ignore )
   str = ignore_set( str, ignore )
   return from_basexx( string.upper( str ), base32Alphabet,  )
end

function basexx.to_base32( str )
   return to_basexx( str, base32Alphabet, , base32PadMap[ #str %  +  ] )
end

--------------------------------------------------------------------------------
-- crockford: http://www.crockford.com/wrmg/base32.html
--------------------------------------------------------------------------------

local crockfordAlphabet = "0123456789ABCDEFGHJKMNPQRSTVWXYZ"
local crockfordMap = { O = "", I = "", L = "" }

function basexx.from_crockford( str, ignore )
   str = ignore_set( str, ignore )
   str = string.upper( str )
   str = str:gsub( '[ILOU]', function( c ) return crockfordMap[ c ] end )
   return from_basexx( str, crockfordAlphabet,  )
end

function basexx.to_crockford( str )
   return to_basexx( str, crockfordAlphabet, , "" )
end

--------------------------------------------------------------------------------
-- base64 decode and encode function
--------------------------------------------------------------------------------

local base64Alphabet = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"..
                       "abcdefghijklmnopqrstuvwxyz"..
                       "0123456789+/"
local base64PadMap = { "", "==", "=" }

function basexx.from_base64( str, ignore )
   str = ignore_set( str, ignore )
   return from_basexx( str, base64Alphabet,  )
end

function basexx.to_base64( str )
   return to_basexx( str, base64Alphabet, , base64PadMap[ #str %  +  ] )
end

--------------------------------------------------------------------------------
-- URL safe base64 decode and encode function
--------------------------------------------------------------------------------

local url64Alphabet = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"..
                      "abcdefghijklmnopqrstuvwxyz"..
                      "0123456789-_"

function basexx.from_url64( str, ignore )
   str = ignore_set( str, ignore )
   return from_basexx( str, url64Alphabet,  )
end

function basexx.to_url64( str )
   return to_basexx( str, url64Alphabet, , "" )
end

--------------------------------------------------------------------------------
--
--------------------------------------------------------------------------------

local function length_error( len, d )
   return string.format( "invalid length: %d - must be a multiple of %d", len, d )
end

local z85Decoder = { 0x00, 0x44, 0x00, 0x54, 0x53, 0x52, 0x48, 0x00,
                     0x4B, 0x4C, 0x46, 0x41, 0x00, 0x3F, 0x3E, 0x45,
                     0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07,
                     0x08, 0x09, 0x40, 0x00, 0x49, 0x42, 0x4A, 0x47,
                     0x51, 0x24, 0x25, 0x26, 0x27, 0x28, 0x29, 0x2A,
                     0x2B, 0x2C, 0x2D, 0x2E, 0x2F, 0x30, 0x31, 0x32,
                     0x33, 0x34, 0x35, 0x36, 0x37, 0x38, 0x39, 0x3A,
                     0x3B, 0x3C, 0x3D, 0x4D, 0x00, 0x4E, 0x43, 0x00,
                     0x00, 0x0A, 0x0B, 0x0C, 0x0D, 0x0E, 0x0F, 0x10,
                     0x11, 0x12, 0x13, 0x14, 0x15, 0x16, 0x17, 0x18,
                     0x19, 0x1A, 0x1B, 0x1C, 0x1D, 0x1E, 0x1F, 0x20,
                     0x21, 0x22, 0x23, 0x4F, 0x00, 0x50, 0x00, 0x00 }

function basexx.from_z85( str, ignore )
   str = ignore_set( str, ignore )
   if ( #str %  ) ~=  then
      return nil, length_error( #str,  )
   end

   local result = {}

   local value =
   for i = , #str do
      local index = string.byte( str, i ) -
      if index <  or index >= #z85Decoder then
         return nil, unexpected_char_error( str, i )
      end
      value = ( value *  ) + z85Decoder[ index ]
      if ( i %  ) ==  then
         local divisor =  *  *
         while divisor ~=  do
            local b = math.floor( value / divisor ) %
            table.insert( result, string.char( b ) )
            divisor = math.floor( divisor /  )
         end
         value =
      end
   end

   return table.concat( result )
end

local z85Encoder = ""..
                   "abcdefghijklmnopqrstuvwxyz"..
                   "ABCDEFGHIJKLMNOPQRSTUVWXYZ"..
                   ".-:+=^!/*?&<>()[]{}@%$#"

function basexx.to_z85( str )
   if ( #str %  ) ~=  then
      return nil, length_error( #str,  )
   end

   local result = {}

   local value =
   for i = , #str do
      local b = string.byte( str, i )
      value = ( value *  ) + b
      if ( i %  ) ==  then
         local divisor =  *  *  *
         while divisor ~=  do
            local index = ( math.floor( value / divisor ) %  ) +
            table.insert( result, z85Encoder:sub( index, index ) )
            divisor = math.floor( divisor /  )
         end
         value =
      end
   end

   return table.concat( result )
end

return basexx

　　兼容 LuaJIT 接口的 ffi 实现，源自 这里，我直接编译得到了 so 文件（见压缩包里的 ffi.so）。

　　然后是 rsautils.lua：

local ffi = require('ffi')
local rsa = ffi.load('./librsa')
local basexx = require('basexx')

local _M = {}

ffi.cdef[[
int public_encrypt(unsigned char * data,int data_len,unsigned char * key, unsigned char *encrypted);
int private_decrypt(unsigned char * enc_data,int data_len,unsigned char * key, unsigned char *decrypted);

int private_encrypt(unsigned char * data,int data_len,unsigned char * key, unsigned char *encrypted);
int public_decrypt(unsigned char * enc_data,int data_len,unsigned char * key, unsigned char *decrypted);
]]

local RSA_PUBLIC_KEY = [[-----BEGIN PUBLIC KEY-----
MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQC3bTBJNQJjY6u7Y5b2eOWws0yW
CGuWPm6MGOSVan65wCrJa5p3q3sodQUDVPotjsknjLlje9E1F7Bx94ZuqTwkvAr6
ieLkgbbeqTCzeJ0AryUXiF3auxFSPdpBoD6nxtEeN8bZwfa/IYzdKyKlbhiQbUMN
qWgmxiPVwupwAML7RQIDAQAB
-----END PUBLIC KEY-----]]

local RSA_PRIV_KEY = [[-----BEGIN RSA PRIVATE KEY-----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-----END RSA PRIVATE KEY-----]]

function _M.rsa_encrypt(plainText)
    local c_str = ffi.new("char[?]",  / )
    ffi.copy(c_str, plainText)
    local pub = ffi.new("char[?]", #RSA_PUBLIC_KEY)
    ffi.copy(pub, RSA_PUBLIC_KEY)
    local cipherText = ffi.new("char[?]", )
    local cipherLen = rsa.public_encrypt(c_str, #plainText, pub, cipherText)
    if cipherLen == - then
        return -, nil
    end
    return cipherLen, basexx.to_base64(ffi.string(cipherText, cipherLen))
end

function _M.rsa_decrypt(cipherLen, b64cipherText)
    local c_str = ffi.new("char[?]", cipherLen + )
    ffi.copy(c_str, basexx.from_base64(b64cipherText))
    local pri = ffi.new("char[?]", #RSA_PRIV_KEY)
    ffi.copy(pri, RSA_PRIV_KEY)
    local plainText = ffi.new("char[?]", )
    local plainLen = rsa.private_decrypt(c_str, cipherLen, pri, plainText)
    if plainLen == - then
        return nil
    end
    return ffi.string(plainText, plainLen)
end

return _M

　　简单测试：

local rsautils = require('rsautils')

local src_str = "my name is ecofast小0胡！!"
local cipherLen, cipher = rsautils.rsa_encrypt(src_str)
if cipherLen ~= - then
    local plain = rsautils.rsa_decrypt(cipherLen, cipher)
    print("src text:", plain)

    print("=========================")
    local txt2 = rsautils.rsa_decrypt(, "aeMIl3wyPP/DIJLudq49k1YeK9o6QhrScyjy2JHcJ7CmFOpQAmbwLxOe/rWigSYeWbAMUw2MB1KTIsool9zEuOSaoiZtgjfpDvf5g/MZUjPAmDofKVutG9xJNonVoK6usHKVcR7wozq/tJ8h/CUWyKGHnLgkxvU3ObbhLPm/wwI=")
    print("src text2:", txt2)
end

　　后记：或许在某个合适的时候，再写一篇关于（大规模）使用脚本如 Lua、Node.js 等作（游戏）开发的思考，或反思吧。个人而言，非常不倾向较大规模地使用脚本语言作开发。至少，用合适的工具做合适的事——而我们都知道，脚本语言，又名胶水语言。