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Re: GRUB and boot partition

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On 2018-01-03 01:59 PM, David Christensen wrote:
> On 01/03/18 06:45, Gary Dale wrote:
>> On 2018-01-02 02:35 PM, Pascal Hambourg wrote:
>>>
>>> Encryption does not require extra space (except for header and block 
>>> padding). Encrypted data have the same size of cleartext data.
>
> +1
>
>
>> Encryption is similar in concept to compression. 
>
> AFAIK common use on Debian systems:
>
> 1.  Encryption functions [1] are reversible functions that transform 
> data 1:1 in size, and are lossless.
>
> 2.  Compression functions [2] are reversible functions that strive for 
> size ratios of N:1, where N > 1 (uncompressed:compressed), and can be 
> lossless or lossly.
>
>
> A related topic is hashing functions [3] (N:fixed, can be difficult to 
> reverse).
>
>
>> It could even reduce the space requirements.
>
> I'm curious -- can you cite a compressing cipher code that cannot be 
> reduced to independent compression and cipher functions?
>
>
>> Encryption and compression both work by replacing strings of letters 
>> with something else.
>
> I agree that encryption and compression are both forms of coding [4].
>
>
>> Encryption and compression both work by replacing strings of letters 
>> with something else. What we call clear text, for example, is just a  
>> > Caesar cipher where each letter is replaced by a number (its ASCII 
>> code
>> or unicode). 
>
> ASCII [5] is a transliteration code -- replace a token from one 
> alphabet (Roman letters, Arabic numerals, common English symbols, 
> etc.) with a token from another alphabet (7-bit binary number). 
> Spelling, grammar, and meaning are unchanged.
>
>
> The goal of a substitution cipher is to conceal meaning, and can be 
> done without changing alphabets (e.g. rot13 [6]).  Spelling and 
> grammar are unchanged (which facilitates cryptanalysis).
>
>
>> Morse code, on the other hand, replaces common letters with shorter 
>> sequences of dots and dashes than less common letters.
>
> I agree that Morse Code [7] uses frequency-based techniques.
>
>
> David
>
>
> References:
>
> [1] https://en.wikipedia.org/wiki/Encryption
>
> [2] https://en.wikipedia.org/wiki/Data_compression
>
> [3] https://en.wikipedia.org/wiki/Hash_function
>
> [4] https://en.wikipedia.org/wiki/Code
>
> [5] https://en.wikipedia.org/wiki/ASCII
>
> [6] https://en.wikipedia.org/wiki/ROT13
>
> [7] https://en.wikipedia.org/wiki/Morse_code
>

While the intent is different, the techniques are quite similar. One 
once-popular code was to replace all words in a message with 2 numbers 
each, referring to a page & word number within an agreed-upon book. If 
you used it electronically, you could send a binary file where each 
original word was reduced to 2 bytes.

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Re: GRUB and boot partition Pascal Hambourg <pascal@plouf.fr.eu.org> - 2018-01-02 20:40 +0100
  Re: GRUB and boot partition Gary Dale <garydale@torfree.net> - 2018-01-03 15:50 +0100
    Re: GRUB and boot partition David Christensen <dpchrist@holgerdanske.com> - 2018-01-03 20:10 +0100
      Re: GRUB and boot partition Gary Dale <garydale@torfree.net> - 2018-01-05 16:30 +0100
        Re: GRUB and boot partition Richard Hector <richard@walnut.gen.nz> - 2018-01-06 13:10 +0100

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