Wanted to try writing my own SHA256 class in CoffeeScript. Needed to warm back up after a long weekend, where I didn't touch a computer. Didn't get too far today, spent most of my time reading the spec...

gistfile1.coffee

# So far, this is being based off of http://www.movable-type.co.uk/scripts/sha256.html
# http://csrc.nist.gov/publications/fips/fips180-4/fips-180-4.pdf
class SHA2
  # §5.3, *Setting the Initial Hash Value*
  # §5.3.3, *SHA-256*
  H = [
    0x6a09e667, 0xbb67ae85, 0x3c6ef372, 0xa54ff53a, 0x510e527f, 0x9b05688c, 0x1f83d9ab, 0x5be0cd19
  ]
  
  # §4.2.2, *SHA-224 and SHA-256 Constants*
  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
  ]
  
  M = null
   
  W = null
  
  constructor: (mS = "") ->
    # §5, *PREPROCESSING*
    # §5.1, *Padding the Message*
    # §5.1.1, *SHA-1, SHA-224 and SHA-256*
    mS += String.fromCharCode 0x80
    
  parse: ->
    # §5.2, *Parsing the Message*
    # §5.2.1, *SHA-1, SHA-224 and SHA-256*
    l = mS.length / 4 + 2
    n = Math.ceil l / 16
    @M = new Array n
    
    for i in [0..n - 1]
      b = new ArrayBuffer 64
      @M[i] = new Uint32Array b
      for j in [0..15]
        @M[i][j] = 
          mS.charCodeAt(i * 64 + j * 4) << 24 |
          mS.charCodeAt(i * 64 + j * 4 + 1) << 16 |
          mS.charCodeAt(i * 64 + j * 4 + 2) << 8 |
          mS.charCodeAt(i * 64 + j * 4 + 3)
    
    @M[n - 1][14] = ((mS.length - 1) * 8) / Math.pow 2, 32
    @M[n - 1][14] = Math.floor @M[n - 1][14]
    @M[n - 1][15] = ((mS.length - 1) * 8) & 0xffffffff
  
  hash: ->
    # 6.2.2, *Hash Computation*
    # 64, 32-bit words (4 bytes * 8 bits) = 2048
    b = new ArrayBuffer 256
    @W = new Uint32Array b
    
    for n in [0..@M.length - 1]
      @W[t] = @M[n][t] for t in [0..15]
      for t in [16..63]
        @W[t] = (@sigma1(@W[t-2]) + @W[t-7] + @sigma0(@W[t-15]) + @W[t-16]) & 0xffffffff
    

My next goal is to rewrite the parse method. I'd like to move it entirely to typed arrays if possible. This is becoming an exercise in learning to work with bits and bitwise operators.

I've been flipping between the spec on nist.gov and also using the impl available on http://www.movable-type.co.uk/scripts/sha256.html. I felt that I should give credit where it's due, since it's been a help to reference a finished product. A longer term goal is to document and explain what each bitwise operation is doing in the doc.