MessageVerifier implementation for node.js

message_verifier.coffee

crypto   = require 'crypto'

MessageVerifier =
  
  serializer: JSON.stringify
  deserializer: JSON.parse
  
  generate: (data, secret, algorithm) ->
    algorithm ?= 'sha1'
    base64 = (new Buffer(MessageVerifier.serializer(data))).toString('base64')
    hmac = crypto.createHmac(algorithm, secret)
    hmac.update(base64)
    "#{base64}--#{hmac.digest('hex')}"


  verify: (message, secret, algorithm) ->
    algorithm ?= 'sha1'

    [data, signature] = message.split('--', 2)
    hmac = crypto.createHmac(algorithm, secret)
    hmac.update(data)
    digest = hmac.digest('hex')
    
    if digest == signature
      return MessageVerifier.deserializer((new Buffer(data, 'base64')).toString('utf8'))
    else
      throw new Error("Invalid signature!")