Module: Lockbox::Padding

Included in:
Lockbox
Defined in:
lib/lockbox/padding.rb

Constant Summary collapse

PAD_FIRST_BYTE = 
"\x80".b
PAD_ZERO_BYTE = 
"\x00".b

Instance Method Summary collapse

Instance Method Details

#pad(str, size: 16) ⇒ Object

ISO/IEC 7816-4 same as Libsodium libsodium.gitbook.io/doc/padding apply prior to encryption note: current implementation does not try to minimize side channels

Raises:

  • (ArgumentError) 


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# File 'lib/lockbox/padding.rb', line 12

def pad(str, size: 16)
  raise ArgumentError, "Invalid size" if size < 1

  str = str.dup.force_encoding(Encoding::BINARY)

  pad_length = size - 1
  pad_length -= str.bytesize % size

  str << PAD_FIRST_BYTE
  pad_length.times do
    str << PAD_ZERO_BYTE
  end

  str
end

#unpad(str, size: 16) ⇒ Object

note: current implementation does not try to minimize side channels

Raises:

  • (ArgumentError) 


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# File 'lib/lockbox/padding.rb', line 30

def unpad(str, size: 16)
  raise ArgumentError, "Invalid size" if size < 1

  if str.encoding != Encoding::BINARY
    str = str.dup.force_encoding(Encoding::BINARY)
  end

  i = 1
  while i <= size
    case str[-i]
    when PAD_ZERO_BYTE
      i += 1
    when PAD_FIRST_BYTE
      return str[0..-(i + 1)]
    else
      break
    end
  end

  raise Lockbox::PaddingError, "Invalid padding"
end