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module Lockbox
module Padding
PAD_FIRST_BYTE = "\x80".b
PAD_ZERO_BYTE = "\x00".b
def pad(str, **options)
pad!(str.dup, **options)
end
def unpad(str, **options)
unpad!(str.dup, **options)
end
# ISO/IEC 7816-4
# same as Libsodium
# https://libsodium.gitbook.io/doc/padding
# apply prior to encryption
# note: current implementation does not
# try to minimize side channels
def pad!(str, size: 16)
raise ArgumentError, "Invalid size" if size < 1
str.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
# note: current implementation does not
# try to minimize side channels
def unpad!(str, size: 16)
raise ArgumentError, "Invalid size" if size < 1
str.force_encoding(Encoding::BINARY)
i = 1
while i <= size
case str[-i]
when PAD_ZERO_BYTE
i += 1
when PAD_FIRST_BYTE
str.slice!(-i..-1)
return str
else
break
end
end
raise Lockbox::PaddingError, "Invalid padding"
end
end
end
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