SHA2 implementation (sha2.lua)

-- Taken from http://lua-users.org/wiki/SecureHashAlgorithm
-- The code here was originally written by Roberto Ierusalimschy,
-- and is licensed under MIT (see http://lua-users.org/lists/lua-l/2014-08/msg00628.html)

-- SHA-256 code in Lua 5.2; based on the pseudo-code from
-- Wikipedia (http://en.wikipedia.org/wiki/SHA-2)

local band, rrotate, bxor, rshift, bnot =
  bit32.band, bit32.rrotate, bit32.bxor, bit32.rshift, bit32.bnot

local string, setmetatable, assert = string, setmetatable, assert

_ENV = nil

-- Initialize table of round constants
-- (first 32 bits of the fractional parts of the cube roots of the first
-- 64 primes 2..311):
local k = {
   0x428a2f98, 0x71374491, 0xb5c0fbcf, 0xe9b5dba5,
   0x3956c25b, 0x59f111f1, 0x923f82a4, 0xab1c5ed5,
   0xd807aa98, 0x12835b01, 0x243185be, 0x550c7dc3,
   0x72be5d74, 0x80deb1fe, 0x9bdc06a7, 0xc19bf174,
   0xe49b69c1, 0xefbe4786, 0x0fc19dc6, 0x240ca1cc,
   0x2de92c6f, 0x4a7484aa, 0x5cb0a9dc, 0x76f988da,
   0x983e5152, 0xa831c66d, 0xb00327c8, 0xbf597fc7,
   0xc6e00bf3, 0xd5a79147, 0x06ca6351, 0x14292967,
   0x27b70a85, 0x2e1b2138, 0x4d2c6dfc, 0x53380d13,
   0x650a7354, 0x766a0abb, 0x81c2c92e, 0x92722c85,
   0xa2bfe8a1, 0xa81a664b, 0xc24b8b70, 0xc76c51a3,
   0xd192e819, 0xd6990624, 0xf40e3585, 0x106aa070,
   0x19a4c116, 0x1e376c08, 0x2748774c, 0x34b0bcb5,
   0x391c0cb3, 0x4ed8aa4a, 0x5b9cca4f, 0x682e6ff3,
   0x748f82ee, 0x78a5636f, 0x84c87814, 0x8cc70208,
   0x90befffa, 0xa4506ceb, 0xbef9a3f7, 0xc67178f2,
}


-- transform a string of bytes in a string of hexadecimal digits
local function str2hexa (s)
  local h = string.gsub(s, ".", function(c)
              return string.format("%02x", string.byte(c))
            end)
  return h
end


-- transform number 'l' in a big-endian sequence of 'n' bytes
-- (coded as a string)
local function num2s (l, n)
  local s = ""
  for i = 1, n do
    local rem = l % 256
    s = string.char(rem) .. s
    l = (l - rem) / 256
  end
  return s
end

-- transform the big-endian sequence of four bytes starting at
-- index 'i' in 's' into a number
local function s232num (s, i)
  local n = 0
  for i = i, i + 3 do
    n = n*256 + string.byte(s, i)
  end
  return n
end


-- append the bit '1' to the message
-- append k bits '0', where k is the minimum number >= 0 such that the
-- resulting message length (in bits) is congruent to 448 (mod 512)
-- append length of message (before pre-processing), in bits, as 64-bit
-- big-endian integer
local function preproc (msg, len)
  local extra = -(len + 1 + 8) % 64
  len = num2s(8 * len, 8)    -- original len in bits, coded
  msg = msg .. "\128" .. string.rep("\0", extra) .. len
  assert(#msg % 64 == 0)
  return msg
end


local function initH224 (H)
  -- (second 32 bits of the fractional parts of the square roots of the
  -- 9th through 16th primes 23..53)
  H[1] = 0xc1059ed8
  H[2] = 0x367cd507
  H[3] = 0x3070dd17
  H[4] = 0xf70e5939
  H[5] = 0xffc00b31
  H[6] = 0x68581511
  H[7] = 0x64f98fa7
  H[8] = 0xbefa4fa4
  return H
end


local function initH256 (H)
  -- (first 32 bits of the fractional parts of the square roots of the
  -- first 8 primes 2..19):
  H[1] = 0x6a09e667
  H[2] = 0xbb67ae85
  H[3] = 0x3c6ef372
  H[4] = 0xa54ff53a
  H[5] = 0x510e527f
  H[6] = 0x9b05688c
  H[7] = 0x1f83d9ab
  H[8] = 0x5be0cd19
  return H
end


local function digestblock (msg, i, H)

    -- break chunk into sixteen 32-bit big-endian words w[1..16]
    local w = {}
    for j = 1, 16 do
      w[j] = s232num(msg, i + (j - 1)*4)
    end

    -- Extend the sixteen 32-bit words into sixty-four 32-bit words:
    for j = 17, 64 do
      local v = w[j - 15]
      local s0 = bxor(rrotate(v, 7), rrotate(v, 18), rshift(v, 3))
      v = w[j - 2]
      local s1 = bxor(rrotate(v, 17), rrotate(v, 19), rshift(v, 10))
      w[j] = w[j - 16] + s0 + w[j - 7] + s1
    end

    -- Initialize hash value for this chunk:
    local a, b, c, d, e, f, g, h =
        H[1], H[2], H[3], H[4], H[5], H[6], H[7], H[8]

    -- Main loop:
    for i = 1, 64 do
      local s0 = bxor(rrotate(a, 2), rrotate(a, 13), rrotate(a, 22))
      local maj = bxor(band(a, b), band(a, c), band(b, c))
      local t2 = s0 + maj
      local s1 = bxor(rrotate(e, 6), rrotate(e, 11), rrotate(e, 25))
      local ch = bxor (band(e, f), band(bnot(e), g))
      local t1 = h + s1 + ch + k[i] + w[i]

      h = g
      g = f
      f = e
      e = d + t1
      d = c
      c = b
      b = a
      a = t1 + t2
    end

    -- Add (mod 2^32) this chunk's hash to result so far:
    H[1] = band(H[1] + a)
    H[2] = band(H[2] + b)
    H[3] = band(H[3] + c)
    H[4] = band(H[4] + d)
    H[5] = band(H[5] + e)
    H[6] = band(H[6] + f)
    H[7] = band(H[7] + g)
    H[8] = band(H[8] + h)

end


local function finalresult224 (H)
  -- Produce the final hash value (big-endian):
  return
    str2hexa(num2s(H[1], 4)..num2s(H[2], 4)..num2s(H[3], 4)..num2s(H[4], 4)..
             num2s(H[5], 4)..num2s(H[6], 4)..num2s(H[7], 4))
end


local function finalresult256 (H)
  -- Produce the final hash value (big-endian):
  return
    str2hexa(num2s(H[1], 4)..num2s(H[2], 4)..num2s(H[3], 4)..num2s(H[4], 4)..
             num2s(H[5], 4)..num2s(H[6], 4)..num2s(H[7], 4)..num2s(H[8], 4))
end


----------------------------------------------------------------------
local HH = {}    -- to reuse

local function hash224 (msg)
  msg = preproc(msg, #msg)
  local H = initH224(HH)

  -- Process the message in successive 512-bit (64 bytes) chunks:
  for i = 1, #msg, 64 do
    digestblock(msg, i, H)
  end

  return finalresult224(H)
end


local function hash256 (msg)
  msg = preproc(msg, #msg)
  local H = initH256(HH)

  -- Process the message in successive 512-bit (64 bytes) chunks:
  for i = 1, #msg, 64 do
    digestblock(msg, i, H)
  end

  return finalresult256(H)
end
----------------------------------------------------------------------
local mt = {}

local function new256 ()
  local o = {H = initH256({}), msg = "", len = 0}
  setmetatable(o, mt)
  return o
end

mt.__index = mt

function mt:add (m)
  self.msg = self.msg .. m
  self.len = self.len + #m
  local t = 0
  while #self.msg - t >= 64 do
    digestblock(self.msg, t + 1, self.H)
    t = t + 64
  end
  self.msg = self.msg:sub(t + 1, -1)
end


function mt:close ()
  self.msg = preproc(self.msg, self.len)
  self:add("")
  return finalresult256(self.H)
end
----------------------------------------------------------------------

return {
  hash224 = hash224,
  hash256 = hash256,
  new256 = new256,
}