docs: def scrypt(password, salt, N=SCRYPT_N, r=SCRYPT_r, p=SCRYPT_p, olen=64):
      """Returns a key derived using the scrypt key-derivarion function
  
      N must be a power of two larger than 1 but no larger than 2 ** 63 (insane)
      r and p must be positive numbers such that r * p < 2 ** 30
  
      The default values are:
      N -- 2**14 (~16k)
      r -- 8
      p -- 1
  
      Memory usage is proportional to N*r. Defaults require about 16 MiB.
      Time taken is proportional to N*p. Defaults take <100ms of a recent x86.
  
      The last one differs from libscrypt defaults, but matches the 'interactive'
      work factor from the original paper. For long term storage where runtime of
      key derivation is not a problem, you could use 16 as in libscrypt or better
      yet increase N if memory is plentiful.
      """
  
      check_args(password, salt, N, r, p, olen)
  
      # Everything is lists of 32-bit uints for all but pbkdf2
      try:
          B  = _pbkdf2('sha256', password, salt, 1, p * 128 * r)
          B  = list(struct.unpack('<%dI' % (len(B) // 4), B))
          XY = [0] * (64 * r)
          V  = [0] * (32 * r * N)
      except (MemoryError, OverflowError):
          raise ValueError("scrypt parameters don't fit in memory")
  
      for i in xrange(p):
          smix(B, i * 32 * r, r, N, V, XY)
  
      B = struct.pack('<%dI' % len(B), *B)
      return _pbkdf2('sha256', password, B, 1, olen)