# File lib/hmac.rb, line 42
    def set_key(key)
      # If key is longer than the block size, apply hash function
      # to key and use the result as a real key.
      key = @algorithm.digest(key) if key.size > @block_size
      akey = key.unpack("C*")
      key_xor_ipad = ("\x36" * @block_size).unpack("C*")
      key_xor_opad = ("\x5C" * @block_size).unpack("C*")
      for i in 0 .. akey.size - 1
        key_xor_ipad[i] ^= akey[i]
        key_xor_opad[i] ^= akey[i]
      end
      @key_xor_ipad = key_xor_ipad.pack("C*")
      @key_xor_opad = key_xor_opad.pack("C*")
      @md = @algorithm.new
      @initialized = true
    end