module Twofish::Padding

Implements padding modes to make plaintext into a complete number of blocks before encryption and to remove that padding after successful decryption.

The only implemented padding schemes are :none and :zero_byte. Note that zero byte padding is potentially dangerous because if the plaintext terminates in zero bytes then these will be erroneously removed by unpad. A more sensible padding scheme should be used in this case.

Constants

ALL: Array of all known paddings.
DEFAULT: Default padding (none).
NONE: Use no padding.
ZERO_BYTE: Use zero byte padding.

Public Class Methods

pad(plaintext, block_size, scheme=DEFAULT) click to toggle source

Pad the given plaintext to a complete number of blocks, returning a new string. See pad!.

# File lib/twofish/padding.rb, line 37
def self.pad(plaintext, block_size, scheme=DEFAULT)
  self.pad!(plaintext.dup, block_size, scheme)
end

pad!(plaintext, block_size, scheme=DEFAULT) click to toggle source

Pad the given plaintext to a complete number of blocks, returning a new string. If the padding scheme is :none and the plaintext is not a whole number of blocks then ArgumentError is thrown.

# File lib/twofish/padding.rb, line 45
def self.pad!(plaintext, block_size, scheme=DEFAULT)
  remainder = plaintext.length % block_size
  case validate(scheme)
  when NONE
    raise ArgumentError, "no padding scheme specified and plaintext length is not a multiple of the block size" unless remainder.zero?
    plaintext
  when ZERO_BYTE
    remainder.zero? ? plaintext : plaintext << "\00"" * (block_size - remainder)
  end
end

unpad(plaintext, block_size, scheme=DEFAULT) click to toggle source

Unpad the given plaintext using the given scheme, returning a new string. See unpad!.

# File lib/twofish/padding.rb, line 58
def self.unpad(plaintext, block_size, scheme=DEFAULT)
  self.unpad!(plaintext.dup, block_size, scheme)
end

unpad!(plaintext, block_size, scheme=DEFAULT) click to toggle source

Unpad the given plaintext in place using the given scheme.

# File lib/twofish/padding.rb, line 63
def self.unpad!(plaintext, block_size, scheme=DEFAULT)
  case validate(scheme)
  when NONE
    plaintext.dup
  when ZERO_BYTE
    plaintext.sub(%r\0000+\Z/, '')
  end
end

validate(scheme) click to toggle source

Takes a string or symbol and returns the lowercased symbol representation if this is a recognized padding scheme. Otherwise, throws ArgumentError.

# File lib/twofish/padding.rb, line 29
def self.validate(scheme)
  scheme_sym = scheme.nil? ? DEFAULT : scheme.to_s.downcase.to_sym
  raise ArgumentError, "unknown padding scheme #{scheme.inspect}" unless ALL.include? scheme_sym
  scheme_sym
end